Principles of Ultrasonography

Similar to sonar used by submarines and fishing boats, ultrasonographic technology analyzes echoes from pulsed sound waves to generate images. Real-time sonography provides continuously updated or “live” images while the patient is being scanned. Live images often allow the clinician to immediately exclude certain diagnoses and to redirect clinical suspicions elsewhere. Live images may also improve the clinician’s understanding of a particular patient’s underlying anatomy. In addition, the best images are often obtained when scanning “live” because the clinician can immediately reposition the patient, if needed.

One general principle of ultrasonography is that the higher the frequency, the sharper the resolution of the image. However, the higher the frequency, the less depth of penetration there is into tissue (Fig. 225-1). With these principles in mind, the clinician chooses the probe, or transducer, that best matches his or her needs. Although recently developed probes can actually change between frequencies, most probes are dedicated to one frequency range—a high- (7.5 to 10 megahertz [MHz]), an intermediate- (5 to 7.5 MHz), or a low- (3.5 to 5 MHz) frequency probe. High-frequency probes are useful for scanning tissue close to the skin surface, such as breast or thyroid lumps, testicles, arteries, veins, or foreign bodies in the skin. Low-frequency probes are useful for scanning deep internal structures such as those of the abdomen, pelvis, and chest. (Even lower-frequency probes [2 to 2.25 MHz] are being used to scan obese patients.) Intermediate-frequency probes may be useful for scanning children. Linear probes are elongated and use parallel sound waves to produce a square or rectangular image (Fig. 225-2A). They require more surface contact, basically throughout the length of the probe, than sector probes. With sector probes, sound waves originate from one point source and are directed through a field to produce a pie-shaped image (Fig. 225-2B). Curvilinear probes are basically linear probes with a curved surface, also requiring less surface contact (Fig. 225-2C) and making it easier to scan areas where it is difficult to maintain good surface contact with a linear probe (e.g., between ribs).

Figure 225-1 A, High-frequency probe (7.5 to 10 MHz) provides higher-resolution images but cannot be used to scan deep organs. This probe is especially useful for organs or structures near the skin surface such as breast or thyroid tissue, veins, or arteries. B, Low-frequency probe (3.5 to 5 MHz) for deeper tissue such as abdominal or pelvic organs.

Figure 225-2 A, Linear probe produces a rectangular image and works especially well for obstetric scans. B, Wedge-shaped image produced by sector scanning probe may be adequate for most applications, depending on width of image. C, Curvilinear probe may be easier to maneuver between ribs. Note wedge-shaped image with curved anterior edge.

Another principle of ultrasonography is that sound waves travel more readily and rapidly through solids and liquids than through air. Consequently, organs that are predominantly air filled (e.g., lungs, bowel), or any organs posterior to or surrounded by air-filled organs, may be difficult to image with sonography. In contrast, the liver, spleen, heart, bladder, and uterus (during pregnancy) are predominantly fluid filled and therefore provide their own excellent “windows” for imaging. They also provide windows to view surrounding organs or structures. A “window” is an area or organ near the body surface through which sound waves can easily be transmitted to obtain images. For tissue very close to the skin surface, such as thyroid, breast, and femoral veins, there is little tissue to be used for a window. In other words, there is little fluid between the probe and the organ. As a result, high-frequency probes often have their own built-in windows. Because ultrasound is best transmitted through solids and liquids, ample acoustic gel must also be applied between the body surface and any probe to form a good interface. Nevertheless, even with ample gel applied and excellent equipment, there will sometimes be difficulty obtaining images of certain organs for various reasons (e.g., inadequate window, organ obscured by bowel gas, body habitus, local trauma). In that situation, the reasons for being unable to scan an area or an organ should be documented and other imaging modalities considered.

note: An after-market standoff or water path can usually be purchased and attached to a low-frequency probe so that, in addition to scanning deep organs, the same probe can be used for scanning near the body surface. If the clinician is not concerned about seeing bubbles, a bag of intravenous (IV) fluid can be used in the same manner, even if it is sometimes awkward to scan through it. Although a higher-frequency probe would certainly produce better images in this situation, for beginners, using a standoff with a low-frequency probe can save the cost of a high-frequency probe. This allows the primary care clinician to become very proficient with his or her “workhorse” or primary probe, usually a low-frequency 3.5-MHz probe.

Fluid such as amniotic fluid, urine, pus, or blood in the aorta or inferior vena cava appears dark by convention on an ultrasonographic image and is sonolucent (sound waves pass through it). Predominantly fluid-filled organs such as the liver, spleen, or renal cortex appear dark or gray on the screen with intermittent bright echoes within their structure. Solid objects such as polyps, bones, or gallstones are white or echogenic (i.e., produce a lot of echoes). If a solid object (calcified or hardened such as a gallstone) is larger than 3 mm, it should cast a well-defined shadow. This type of well-demarcated or “sharp” shadow can be differentiated from shadows cast by air, such as air in the gut. Artifact and shadows produced by air are often diffuse or “soft” and change considerably with changes in the placement, angle, or pressure of the probe or with peristalsis.

From a sonographic perspective, a cyst is any fluid-filled structure with smooth walls. Examples include cysts in the ovary, liver, or kidney, but also a full gallbladder, uterus during pregnancy, or full urinary bladder. In some ways, the inferior vena cava and abdominal aorta demonstrate cystic properties, such as the following:

Because of the third property, cystic structures often serve as excellent windows for tissue being scanned behind or around them. The fourth property manifests as “semishadows,” or what appear to be shadows, often seen below both sides of a cyst and spreading outward (i.e., the penumbra effect). Combined, the appearance of all four acoustic properties may help confirm that whatever is being scanned is a cystic structure. These phenomena may be important after localizing a palpable mass, especially when trying to determine whether it is truly a cyst and might benefit from draining, or whether it is an adenoma.

Quality Assurance

For diagnostic purposes, to maximize accuracy and to minimize liability—especially for emergency scans—again, perhaps only limited, goal-directed scans should be performed. If the patient is possibly unstable, there may be time only for a limited study. Limited or focused studies can be used to answer a particular clinical question, to improve patient care, or as a follow-up to streamline patient care. Similar to interpreting plain radiographs, the clinician at the bedside knows exactly where the patient is experiencing pain. This information is helpful when interpreting limited scans, especially when there are abnormalities. In complex cases or in cases in which portable ultrasonography is inconclusive, if the patient is stable, referral for a formal study can be considered. If the clinical question cannot be answered with certainty, referral or consultation should be considered, especially if it might change the management. If these principles are followed, perhaps the rare yet most dreaded error of failure to diagnose can be avoided.

A quality assurance program should be implemented. This could consist of some method of tracking outcomes or comparing results. One method of comparing outcomes while the clinician is learning is to not charge for “beginner” or “learner” scans and to follow up every scan with a formal scan in the radiology department. Log sheets should be created and used to compare results with formal scans. Results should continue to be compared until an acceptable level of clinical accuracy is achieved. Although formal interpretations may differ slightly from “beginner” or “learner” interpretations, the evaluation standard is whether the formal interpretation will lead to a change in clinical management. Having a radiologist over-read every scan is another method of ensuring quality; standard images could be obtained with each scan and then reviewed by a radiologist. Internet over-reading services by a radiologist are now continuously available (see the Suppliers section). With either method of quality assurance, proof of high-quality clinical data can be maintained and liability minimized, especially the liability of failure to diagnose. With these methods of quality assurance, the process of verifying and documenting clinician competence can be customized for each individual clinician.

For procedural purposes, there has been speculation that national hospital accrediting organizations will someday require many emergency department and hospital procedures to be ultrasonography guided. At the time of this publication, the author informally surveyed hospitalists and emergency medicine experts and found that none saw the need for such guidelines. Although there is individual variation, the literature suggests that the vast majority (>80%) of hospital and emergency medicine procedures are not currently ultrasonography guided. The majority of clinicians use ultrasonographic guidance only in those patients with a challenging body habitus or when there has been difficulty performing a procedure.

As with many procedures in primary care, beginners should develop a relationship with a consultant, either a radiologist or a clinician competent with ultrasonography (sonologist). Ultrasonography technicians (sonographers) often have extensive skill in multiple areas of ultrasonography and can be helpful consultants, especially in rural areas. As the clinician begins performing ultrasonography, cases should be discussed and consultation or supervision should be available.

Credentialing

For departments implementing ultrasonography as a procedure, in addition to quality assurance, policies should be in place regarding credentialing. Such policies should identify eligible providers, specify training or experience requirements, and specify the ultrasonography privileges. For certain clinicians, ultrasonography can seem quite simplistic, and it can even be seductive; operators may become overconfident. Without credentialing, the liability of failing to diagnose may increase with potentially catastrophic outcomes, especially in urgent care centers or emergency departments. The author knows of cases in which watchful waiting (e.g., leaking abdominal aortic aneurysm, ectopic pregnancy) was inappropriate management. These near-catastrophes could have been avoided with appropriate departmental policies, credentialing, or a supervision process.

Reasonable guidelines for credentialing nonradiologists in an emergency department require a minimum of 150 recorded scans for general emergency ultrasonography privileges or 25 scans per primary indication. For procedural ultrasonography, the clinician should demonstrate competence in the use of basic ultrasonography by being credentialed for at least one primary indication. ACEP (and the literature) supports these numbers and notes that the range needed to document proficiency is between 25 to 50 scans per primary indication. These scans should be followed up with formal scans, over-reading, or by tracking clinical outcomes to document and demonstrate accuracy. At least 50% of the scans should show an abnormality. When competence for primary scans has been documented, scanning for other diagnoses (extended scans) can be managed on a case-by-case basis. Although there is much more to ultrasonography than can be learned by performing a certain number of scans, using these numbers as guidelines is helpful when attempting to decide whether a clinician is ready to demonstrate competence. There is also a process by which clinicians can be certified as registered diagnostic medical sonographers (RDMSs) after passing certain examinations and being supervised with scanning. It should be noted that the American Academy of Family Physicians does not endorse using a particular number of procedures performed (or documented) to credential for this or most other procedures.

Liability

When deciding whether using ultrasonography will raise a clinician’s liability, the risk of not having ultrasonography immediately available should be weighed against making an incorrect diagnosis using ultrasound as a nonradiologist. For example, if certain diagnoses are not made urgently (e.g., pericardial tamponade, ectopic pregnancy, leaking aortic aneurysm, hemoperitoneum), patients may be endangered and liability may increase. In fact, failure to diagnose ectopic pregnancy is the second leading cause (in total dollar amounts) of malpractice awards against emergency physicians; ultrasonography is the initial procedure of choice to exclude ectopic pregnancy. For these and many other reasons, emergency clinicians now perform ultrasonography in most large emergency departments. Since ultrasonography training became routine for residents in emergency medicine, the standard of care also changed to that of a prudent emergency department physician, not a radiologist. Unfortunately, the standards of care for hospitalists and other primary care clinicians are not as well defined; therefore, documentation of competence, absolute certainty of interpretation, and over-reading may be important.

Documentation

In many cases, ultrasonographic images are interpreted by the primary care clinician as they are being obtained. These interpretations often guide contemporaneous clinical decisions; however, a report needs to be placed on the patient’s chart. It can be a hand-written, dictated, or templated note and should include the indication for the ultrasonography (e.g., preliminary diagnosis), what organs or structures were imaged, a copy of recorded images, appropriate measurements, and the final interpretation. If bowel gas or other technical factors prevent a thorough scan, these limitations should be identified and documented. Whenever feasible, images should be stored as part of the medical record and done so in accordance with facility policy requirements. Documentation is especially important if the clinician will be billing for ultrasonography; however, given the possible emergent use of ultrasonography by primary care clinicians, the timely delivery of care should not be delayed to archive images.

Equipment

Beginner Scanning

Most clinicians learn human anatomy in three dimensions by dissection. Interpreting ultrasonographic images requires an ability to translate that knowledge into two dimensions. For proper probe placement and angulations, beginners should know that the best image is generated when the probe is perpendicular to the tissue being studied (Fig. 225-3). It may be helpful for beginners to minimize the planes of anatomy they have to learn by limiting their scanning to transverse and longitudinal planes. In other words, beginners should consider placing the transducer marker dot only toward the patient’s right side (transverse) or head (longitudinal), while holding the probe perpendicular to the organ or tissue being scanned. If the probe can be held perpendicular to the skin surface, it is also usually easier to scan. Even for experienced sonographers, using these techniques may be helpful when getting oriented to a patient’s anatomy at the beginning of any scan.

Figure 225-3 A, Best image is produced when the ultrasound beam is perpendicular to the organ interface. B, When the ultrasound beam is not perpendicular to the organ interface, scatter is seen, which may cause artifacts.

By convention, when the marker dot is to the patient’s right side, it produces a transverse image similar to computed tomography (CT) orientation (Fig. 225-4). The patient’s right side will be to the left of the image on the screen. With the marker dot toward the patient’s head, the image is what the clinician would see if the patient were dissected longitudinally and viewed looking into the body from the right side with the patient’s head to the left of the screen (Fig. 225-5). A good impression of all of the anatomy and images of most organs can be obtained with longitudinal scanning, alone, at first.

Figure 225-4 A, Marker dot toward the patient’s right side produces a transverse image of the abdomen. B, Transverse image: kidneys (A), pancreas (B), liver (C), inferior vena cava (D), and aorta (E).

Figure 225-5 A, Marker dot toward the patient’s head produces a longitudinal image of the abdomen. B, Longitudinal image: gallbladder (A), right kidney (B), perirenal fat (C), liver (D), and diaphragm (E).

note: Some European manufacturers reverse the orientation so that the marker dot is found on the right side of the image.

Indications

Cardiac Ultrasonography

In the unstable hypotensive patient or the patient in shock, if there are narrow QRS complexes on the ECG, the diagnosis is EMD. The differential includes anything that could cause abrupt cessation of venous return to the heart (including massive pulmonary embolism, tension pneumothorax, cardiac tamponade), acute malfunction of a prosthetic valve, and exsanguination. During resuscitative measures, exclusion of reversible causes is imperative, especially tamponade. Cardiac ultrasonography (echocardiography) is the diagnostic procedure of choice for excluding reversible causes of EMD.

A patient with a large pericardial effusion can be completely asymptomatic, deteriorate rapidly as a result of tamponade, or be in between. Several scenarios may lead the clinician to suspect a pericardial effusion (e.g., an enlarged cardiac silhouette on the chest radiograph, electrical alternans or decreased voltage on an ECG), especially in a patient at risk of an effusion. Pericardial tamponade may also result from a penetrating wound to the chest or be the cause of unexplained hypotension, prominent jugular venous distention, or a pulsus paradoxus on physical examination. Echocardiography is also the diagnostic procedure of choice for identifying and quantifying a pericardial effusion. Because rapid intervention is often a necessity in tamponade, ultrasonically directed aspiration of a hemodynamically significant effusion has become the treatment of choice.

Many emergency department clinicians, hospitalists, and cardiologists now also include a quick portable ultrasound of the heart when evaluating patients with chest pain. (See also Chapter 90, Echocardiography.) With this evaluation, gross cardiac activity can be assessed, including left ventricular function. Wall motion abnormalities (suggesting ischemia or scar) or severe valvular dysfunction may be noted, often early in the evaluation. Intravascular volume status can often be estimated, and right ventricular dysfunction or acute pulmonary hypertension identified (possibly indicating a pulmonary embolism). In the setting of chest pain, occasionally the diagnosis of proximal aortic dissection or a thoracic aortic aneurysm can be made.

Technique

While viewing the front of the chest—if the 12 o’clock position is considered cephalic and the 6 o’clock direction caudal—note that the axis of the heart is directed toward the 4 o’clock position. Placing the marker dot of the transducer at about the 4 o’clock position produces the long-axis view of the heart, especially if the probe is located parasternally. The long-axis view is essentially the longitudinal view of the heart, if described in the conventional terminology of ultrasonography for the remainder of the body. Rotating the marker dot almost 90 degrees to the 8 o’clock position produces the short-axis view of the heart, which is actually a transverse view of the heart (Fig. 225-6). For unresponsive patients, those who cannot be moved, or patients with pulmonary hyperinflation (e.g., chronic obstructive pulmonary disease, intubated), a subxiphoid view may be useful. However, a subxiphoid view may not be possible in patients with abdominal distention or pain, so the clinician should be comfortable using several cardiac windows.

1 With the patient in the supine position, place the low-frequency transducer in the parasternal (third to fourth or fifth intercostal space) or apical (inferolateral to the left nipple at the point of palpated maximal cardiac impulse) location. These are the same two traditional locations used for auscultation with a stethoscope.

2 In the parasternal space, the probe or marker dot will be rotated to either the 4 o’clock (long axis) or 8 o’clock (short axis) position.

3 The short-axis view at the level of the mitral valve is often used to assess the adequacy of the window because the mitral valve is usually prominent and easy to locate. In this view, with the probe directed almost straight posteriorly, nearly perpendicular to the bed, the mitral valve produces the characteristic “fish-mouth” image (Fig. 225-7), especially if there is any degree of stenosis. This is basically a transverse view of the mitral valve. After this transverse view is obtained, if the probe is directed or angled superiorly, toward the patient’s right scapula, the aortic valve can often be seen in cross-section. (This is more of an extended scan, so see also Chapter 90, Echocardiography, and Fig. 90-4.) Conversely, from the transverse view of the mitral valve, if the probe is directed or angled inferiorly, toward the patient’s left hip, the papillary muscles of the mitral valve can be seen in cross-section (see Chapter 90, Echocardiography, Fig. 90-5). They are echogenic (bright white) structures, surrounded by fluid in the heart (dark), which in turn is enclosed by the echogenic left ventricular walls seen in cross-section.

4 Directing the probe straight posteriorly, again perpendicular to the bed, the parasternal long-axis view can be obtained from the short-axis view by simply rotating the probe about 90 degrees counterclockwise (i.e., marker dot directed toward the 4 o’clock position; Fig. 225-8A and B). This is basically a longitudinal view of the mitral valve, with the echogenic ventricular septum located above the mitral valve on the image and the posterior wall located below it. The dark, fluid-filled right ventricle is located above the septum, and the left ventricle below it (Fig. 225-8C). To the right side of the image will be the aortic root, located to the right of the aortic valve and above the left atrium (see Fig. 225-8C). The left atrium in this view is located to the right of the mitral valve. The aortic valve cusps will also be seen opening and closing in a longitudinal view.

5 If the patient’s position can be changed easily, place the patient on his or her left side. This allows the lingula of the lung to fall away from the heart and often provides a better window for all cardiac imaging.

Figure 225-6 Typical probe positions (placement) for emergency department echocardiography: a, parasternal position of probe; b, apical position of probe; and c, probe in subxiphoid position.

Figure 225-7 Short-axis view at mitral valve level. Probe is in parasternal position with marker dot at the 8 o’clock position. A, Ultrasonographic plane transects the short axis of the heart at the level of the mitral valve. B, Actual endocardiac structures viewed with probe in this position. M, mitral valve. C, Short-axis view as it appears on the ultrasonography screen. The image is displayed as if it is being viewed from the apex of the heart looking up toward the base. Note “fish mouth” appearance of mitral valve (M) as seen from this view. IVS, interventricular septum; LV, left ventricle; RV, right ventricle.

Figure 225-8 Parasternal long-axis view of the heart. Probe is in parasternal position with the marker dot at the 4 o’clock position. A, Ultrasonographic plane transects heart through the long axis. B, Actual endocardiac structures viewed. C, Image as it appears on ultrasonography screen. AV, aortic valve; IVS, interventricular septum; LV, left ventricle; MV, mitral valve; RV, right ventricle.

note: Some ultrasound equipment places the marker dot 180 degrees away from this standard orientation (i.e., the 6 o’clock position for some is the 12 o’clock position for others). To allow the user to determine the orientation of the probe, the marker on the image should be found. It corresponds with the marker dot on the probe.

6 In the apical location (again, a more extended scan, so see also Chapter 90, Echocardiography), the majority of scanning can be performed with the marker dot rotated toward the patient’s right side or at the 8 o’clock position. The probe is then directed toward the patient’s right shoulder. The apex of the heart will be in the center at the top of the image, with the septum also in the center and coursing vertically downward. The left ventricle and atrium will be on the right side of the image, and the right ventricle and atrium on the left, so it is called the apical four-chamber view (see Chapter 90, Echocardiography, Fig. 90-7).

7 A subxiphoid view may be needed to obtain a good window. Place the transducer directly below the xiphoid with the marker dot toward the patient’s right side and angle it toward the patient’s left scapula or even higher on the back. In fact, because the heart lies immediately beneath the sternum, the angle or plane of the probe will be almost horizontal or parallel to the patient’s bed. A portion of liver will typically be seen at the top of the image (Fig. 225-9). Firm downward pressure may need to be applied with the probe, especially if the patient has a protuberant abdomen. Cardiac structures from this window will appear similar, but in a mirror image (rotated 180 degrees), to the parasternal long-axis view.

8 Search for fluid posterior to the heart. If present, it will usually appear at the bottom of the image. If found, quantify the amount of fluid (see Fig. 225-10). For various reasons (including body habitus) up to 10% of patients cannot be scanned adequately for a complete echocardiogram with portable equipment, even under optimal conditions. However, almost all patients with a clinically significant effusion can be diagnosed, so scan patiently and methodically. With a significant effusion, almost any view is acceptable. If an effusion is not readily apparent, vary the probe angles and amount of pressure applied on the probe for 5 to 10 minutes, if necessary, to find a window. Changing the patient’s position may be helpful. All of these maneuvers may be necessary when there is a challenging body habitus or too much air in the lungs obscuring the image. If a good window is found with the parasternal short-axis view, many experts suggest using the parasternal long-axis view to exclude an effusion (see Fig. 225-8) because it provides a lengthwise image of the gravity-dependent portion of the heart (the posterior wall) when the patient is lying down. This is where a nonloculated effusion is most likely to settle.

Figure 225-9 Subxiphoid (subcostal) view of heart.

Figure 225-10 Effusions using a parasternal long-axis view. A, Small (may be physiologic). Ao, aortic root; At, left atrium. B, Moderate. C, Large.

note: Even large effusions may develop gradually and not cause EMD or tamponade.

Obstetric–Gynecologic Ultrasonography

With the advent of transvaginal probes, an alternative to transabdominal scanning became available for evaluating the female pelvis. Advantages of transvaginal over transabdominal scanning include the use of a higher-frequency probe with higher resolution, fewer tissue layers through which to scan (nine layers on transabdominal), resulting in less artifact, and less patient preparation required, especially regarding the bladder. These advantages allow an intrauterine pregnancy to be diagnosed by about 5 weeks after the first day of the patient’s last menstrual period. Fetal cardiac activity can frequently be seen by 6 weeks. With transvaginal scanning, there is also a greater likelihood of visualizing an ectopic pregnancy in a tube or the adnexa. Disadvantages to transvaginal scanning include the necessities of an extra probe, a sheath, and additional training. Interpretation is slightly more confusing and the field of imaging is slightly narrower. Despite the fact that patients are becoming more familiar with and accepting of this technology, transvaginal scanning is also slightly more invasive.

Transabdominal Scanning

Preprocedure Patient Preparation

The patient is scanned in the supine position. For an adequate window, the patient’s bladder must be full, occasionally to the point of discomfort. For best scanning, the bladder should be so full that the dome extends 1 or 2 cm above the fundus. If scanning above the pubis does not immediately provide an adequate view, the patient’s clinical stability should be evaluated. If she is stable, either a Foley catheter infusion of fluid (300 to 500 mL) or oral or IV hydration can be used to fill the bladder. If a Foley catheter is used to infuse fluid, the clinician should try to avoid instilling air bubbles into the bladder, which can cause echoes and produce a confusing image.

Technique

1 Scanning the bladder first with a low-frequency probe and the marker dot at the patient’s right side may help determine the shape and orientation of the uterus behind the bladder (Fig. 225-11). Because the bladder is rarely full of floating debris, the gain should be lowered until a minimal number of echoes are demonstrated in the bladder. This will decrease artifact. Confirm that the bladder, as opposed to a large ovarian cyst, is being used as a window. A large ovarian cyst is usually irregularly shaped, is oval or round, and often contains complex or echogenic contents. The bladder is basically square in a transverse view.

2 Turn the marker dot cephalad for a longitudinal view (Fig. 225-12). Often the uterus is not quite in the midline, as will have been demonstrated on the transverse view, so the probe may need to be rotated slightly out of the midline for a longitudinal image of the uterus. An echogenic line in the midline of the uterus is normal and represents the interface between the anterior and posterior endometria. A pair of dark fluid lines anterior and posterior to the central echogenic line represents endometrium during the proliferative phase. During the secretory phase, the endometrium becomes progressively thicker and echogenic. Scan the uterus from fundus to cervix. Occasionally an echogenic line known as the vaginal stripe may be visualized in the vagina, distal to the cervix. It represents another interface.

3 Photograph and document any object or fluid accumulation within the uterus or posterior to it in the cul de sac (pouch of Douglas).

4 Scan the adnexa and note any fluid accumulations or abnormalities. Adnexa are usually located by first finding the midline of the uterus and then rotating the probe slightly. More specifically, with the probe producing a longitudinal view of the uterus, rotate it slightly clockwise (left adnexa) or counterclockwise (right adnexa) so that the marker dot is somewhat oblique to the uterus. If the adnexa cannot be located with this maneuver, move the probe laterally off of the midline and, while maintaining a longitudinal orientation, scan across and through the bladder to the opposite adnexa. In other words, angle the probe about 15 degrees off of the vertical to scan from the patient’s left paramedian position. Scan across the midline through the bladder to visualize the patient’s right adnexa, and vice versa for the left. The ovary often indents the wall of the bladder. Ovaries are oval structures of medium echogenicity and lie immediately anterior and medial to the internal iliac arteries, which are pulsatile and have echogenic walls. The iliac veins are also nearby. In women of reproductive age, demonstration of internal follicles often distinguishes ovaries from surrounding structures. Normal ovaries are 2.5 to 5 cm long, 1.5 to 3 cm wide, and 0.6 to 1.5 cm thick. Evidence of peristalsis on the patient’s left side confirms that the colon is being scanned instead of the ovary.

Figure 225-11 Transverse view of the bladder. Note uterus (UT), viewed transversely, is found posterior to the bladder.

Figure 225-12 Longitudinal view of the bladder. Note uterus (UT), viewed longitudinally, behind the bladder. Fluid in the cul de sac (FL) is found posterior to the uterus. VG, vagina.

Transvaginal Scanning

Preprocedure Patient Preparation

The patient is scanned in the supine or lithotomy position. Transvaginal scanning is usually preceded by transabdominal scanning with a full bladder, perhaps allowing the clinician to make the diagnosis and, if not, to assess the overall anatomy. The bladder can then be emptied; however, some residual urine can serve as a useful marker for locating the bladder.

Technique

1 Prepare the probe by covering it with a probe sheath, a plain-ended latex condom, or an examination glove. Adequate gel should be placed on the tip of the transducer before covering it. Any bubbles between the cover and transducer should be smoothed out before scanning.

2 Perform a preliminary pelvic examination to relax the vagina as well as to evaluate for palpable masses. Determine the size, shape, and position of the uterus and define any areas of tenderness. Any tampons should be removed. Counsel the patient about the transvaginal ultrasonographic examination and obtain verbal consent.

3 While continuing to wear examination gloves, apply more gel to the transducer cover and gently insert the probe with posterior vaginal pressure to a position anterior to the cervix.

4 Scanning starts as soon as the transducer is inserted; avoid inserting the transducer too far, which can cause the clinician to miss the cervix and lower uterine segment. With the marker dot anterior, locate the midline of the uterus in the image.

5 Obtain both longitudinal and coronal scans of the uterus and adnexa by turning the marker dot anterior to the patient or toward her right side. For longitudinal scanning, the image orientation changes slightly (Fig. 225-13) compared with transabdominal scanning. Because the marker dot is pointed toward the anterior abdominal wall of the patient, the left side of the resultant image is actually anterior instead of cranial. Transverse orientation also changes slightly because true anteroposterior (AP) images of the uterus cannot be obtained by scanning from below. However, various coronal images are obtained that are similar to transverse images. The patient’s right side remains on the left side of the image because the marker dot is turned to the patient’s right side (Fig. 225-14).

6 Scan the uterus by performing a series of longitudinal, coronal, and oblique scans with the transducer at varying depths of penetration. Oblique views are obtained by rotating the probe with the marker dot in the longitudinal position to either the right or left side of the patient. Oblique views are used to scan the adnexa.

7 Note any evidence of a fetus or fluid accumulations. Any areas of tenderness should be documented, along with any other important findings.

Figure 225-13 Longitudinal orientation with transvaginal scanning. BL, bladder; UT, uterus.

Figure 225-14 Transverse orientation with transvaginal scanning. UT, uterus.

First-Trimester Vaginal Bleeding

Approximately 25% of all pregnancies experience bleeding during the first half (see Chapter 172, Obstetric Ultrasonography, for differential). Abdominal pain is also common during pregnancy. Ultrasonography is recommended as the first test in patients experiencing bleeding or pain beyond 5 to 7 weeks after their last menstrual period. Two frequent causes of first-trimester vaginal bleeding are ectopic pregnancy and threatened abortion.

note: If a fetal heart beat is demonstrated by the less expensive hand-held Doppler, pregnancy loss has effectively been ruled out and ectopic pregnancy is much less likely. Doppler heart beats are not heard until 9 or 10 weeks, and most ectopic pregnancies become symptomatic before that time. With a threatened abortion, demonstration of fetal heart beats decreases the likelihood of miscarriage to less than 10%. If the Doppler is used during a bimanual pelvic examination and aimed directly at the uterine fundus as it is elevated by the examiner’s hand, the likelihood of hearing fetal heart beats is much improved.

Suspected Ectopic Pregnancy

Ectopic pregnancies vary in prevalence from 1 in 28 to 1 in 200 pregnancies. They account for the majority of first-trimester maternal deaths. The incidence has quadrupled since 1970, and there has been a sevenfold increase in maternal mortality. More than 40% of ectopic pregnancies are misdiagnosed on first presentation to the health care provider.

Clinical ultrasonography coupled with immediately available sensitive radioimmunoassay for human chorionic gonadotropin (hCG) has decreased the morbidity and mortality of ectopic pregnancies. It is important to correlate quantitative hCG levels in your laboratory with the type of equipment available to determine at what level of hCG an intrauterine pregnancy should be visible by sonography. This will vary depending on whether transabdominal or transvaginal scanning is performed.

Risk Factors for Ectopic Pregnancy (in Descending Order of Significance) and Symptoms

• Intrauterine device currently in place or recently used

• Previous tubal, abdominal, or pelvic surgery

• Prior ectopic pregnancy

• Prior sexually transmitted infection, especially pelvic inflammatory disease

• Infertility

• Recent therapeutic abortion

In several large studies, pain (97% to 100% of patients) and amenorrhea (74% to 84%) were more common complaints than vaginal bleeding, although bleeding occurred in the majority of ectopic pregnancies.

Interpretation: Transabdominal Scanning

One technique for excluding or ruling out an ectopic pregnancy is to confirm or rule in an intrauterine pregnancy. With transabdominal scanning, to diagnose an ectopic pregnancy by actually visualizing the fetus in a tube or the adnexa is rare (<10% of ectopic pregnancies). Even with higher-resolution transvaginal scanning, only occasionally will the ectopic pregnancy be visualized (<25% of ectopic pregnancies).

To confirm an intrauterine pregnancy, a gestational sac with a fetus or fetal pole should be noted. A gestational sac appears as an anechoic (dark) structure within the uterus with highly echogenic borders. The first small echogenic structure seen in the gestational sac is the yolk sac at about weeks. About a week later, a small collection of echoes may be seen; they constitute the fetal pole. The presence of a gestational sac with a fetal pole in the uterus reduces the chance of an ectopic pregnancy to about 1 in 30,000 cases. This figure represents the likelihood of a concomitant ectopic during an intrauterine pregnancy, the so-called combination pregnancy. Exceptions to this statistic are found in patients undergoing assisted reproduction in which the risk of combination pregnancy may be as high as 1 in 7000, or in patients taking ovulation-stimulating fertility drugs (e.g., clomiphene), in which the incidence may be as high as 1 in 100. If no fetal pole is seen within what appears to be a gestational sac, the clinician must consider that 10% to 20% of ectopic pregnancies produce pseudogestational sacs in the uterus and that the possibility of an ectopic pregnancy cannot be completely dismissed.

The gold standard for diagnosing an intrauterine pregnancy is the visualization of embryonic cardiac activity. This may be seen as early as 7 weeks after the first day of the patient’s last menstrual period or when the mean sac diameter is 12 to 16 mm, depending on the resolution of the equipment and the skill of the examiner. Mean sac diameter is determined by measuring a single diameter if the sac is round. It is the average of the three largest diameters (transverse, longitudinal, and AP) if the sac is oval. If a fetus is seen, gestational age can also be determined from what else is visualized (Table 225-1). When a gestational sac with a mean diameter greater than 25 mm (17 mm for transvaginal scanning) lacks an embryo or when the gestational sac is grossly distorted, abnormal pregnancy is almost certain. Using these criteria, 76% of abnormal pregnancies and 93% of normal pregnancies will be correctly classified by only one ultrasonographic scan. The most accurate estimate of gestational age is at 9 to 11 weeks, using the crown–rump length.

TABLE 225-1 Dates from Last Menstrual Period Correlated to Findings by Transabdominal Imaging*

Finding	Weeks
Gestational sac	5–6
Yolk sac	5–6
Fetal pole	6–7
Cardiac activity	7–8
Placenta	8–9
Somatic activity	9–10

* Transvaginal imaging can usually locate the same finding 1 week earlier.

If the patient is obese or her bladder is empty, transabdominal ultrasonographic findings may be limited; transvaginal scanning may be the only option. In all cases, failure to define an intrauterine pregnancy is interpreted in the proper clinical setting as an ectopic pregnancy until proven otherwise. Eight options exist when an intrauterine pregnancy is not demonstrated by ultrasonography (Table 225-2). Correlation with hCG titers may be necessary to complete the interpretation. With a healthy intrauterine pregnancy, hCG values rise predictably, doubling every 2 to 3 days for the first 8 weeks. In contrast, the hCG titer tends to rise at a slower rate in a patient with an ectopic pregnancy.

TABLE 225-2 Possible Diagnoses If an Intrauterine Pregnancy Is Not Demonstrated by Transabdominal Ultrasonography

Diagnosis	Finding	Management
Confirmed ectopic pregnancy	Empty uterus and ectopic fetal heart activity	Surgery or emergent consultation
Highly likely ectopic pregnancy	Empty uterus and echogenic pelvic mass or free pelvic fluid or hemoperitoneum	Surgery, culdocentesis or emergent consultation
Very early normal pregnancy	Serum quantitative hCG <6000 mIU/mL IRP (3000–3250 mIU/mL Second Standard)	Repeat quantitative hCG in 48–72 hr
Occult unruptured ectopic pregnancy	Empty uterus or may see pseudogestational sac in uterus (seen in 10%–20% of ectopic pregnancies)	Surgery, consultation, or repeat quantitative hCG in 48–72 hr if stable
Complete or incomplete spontaneous abortion	Empty uterus or atypical echogenic or sonolucent findings in uterus such as a misshapen sac, located low in the uterus, or debris in the sac	D&C to treat or confirm, consultation, or repeat quantitative hCG; emergency treatment necessary if cannot exclude ectopic pregnancy, if patient is unstable, or for heavy bleeding
Dead embryo	Crown–rump length >5 mm and no cardiac motion after continuous observation	Serial quantitative hCGs or repeat ultrasonography in a few days; emergency treatment necessary only for heavy bleeding
Embryonic resorption/blighted ovum	Mean sac diameter of >2.5 cm and no fetal pole or >2.0 cm and no yolk sac (see text for calculating mean sac diameter); also, a misshapen empty sac, located low in uterus, or debris in the sac	Emergency treatment necessary only for heavy bleeding
Hydatidiform mole or trophoblastic disease	Snowstorm appearance of uterine contents	Consultation or D&C

D&C, Dilation and curettage; hCG, human chorionic gonadotropin; IRP, International Reference Preparation.

Evaluation of the medical literature for quantitative hCG titers correlated with sonographic findings often leads to confusion regarding the standards being used (for a crude conversion, the Second International Standard equals about 50% of the International Reference Preparation [IRP]). Most hospital laboratories are currently using the Second International Standard, whereas much of the early research used IRP. If the IRP standard of hCG quantities is used, transabdominal ultrasonography should detect an intrauterine pregnancy in 94% of cases when the quantitative hCG reaches 6000 to 6500 mIU/mL (3000 to 3250 mIU/mL for the Second Standard). This correlates with about 42 days’ gestation.

Even if an ectopic pregnancy is not demonstrated by ultrasonography, there are associated sonographic findings (Table 225-3) that, if seen, significantly increase the likelihood of ectopic pregnancy. In the case of a ruptured ectopic, scanning the upper abdomen may reveal free fluid representing intra-abdominal hemorrhage. Although a moderate to large amount of fluid is highly correlated with an ectopic pregnancy, any free fluid is significant in the proper clinical situation. A demonstrated echogenic pelvic mass also significantly increases the likelihood of ectopic pregnancy.

TABLE 225-3 Using Transabdominal Ultrasonography to Determine Risk of Ectopic Pregnancy in Patients with Positive Human Chorionic Gonadotropin and Empty Uterus

Ancillary Findings	Risk of Ectopic Pregnancy (%)
Any free fluid	20
Echogenic mass	71
Moderate to large amount of fluid	95
Echogenic mass with fluid	100
No ancillary findings	20

If a normal intrauterine pregnancy is demonstrated, the search for other causes of the patient’s symptoms might be facilitated with ultrasonography. The clinician should scan for evidence of urolithiasis, intact or ruptured ovarian or corpus luteum cyst, adnexal/ovarian torsion, tubo-ovarian abscess (dilated fallopian tubes/hydrosalpinx, usually bilateral, indicate pelvic inflammatory disease), or appendiceal abscess (appendicitis). Although a thorough description of the ultrasonographic findings for most of these situations is beyond the scope of this chapter, a ruptured ovarian cyst frequently is noted as an irregular adnexal mass, accompanied by fluid in the cul de sac, and evidence of clotting blood seen as an echogenic mass difficult to separate from the uterus. The appearance will be the same with a ruptured corpus luteum cyst; however, the ovary will be noted in the middle of the irregular adnexal mass. If color Doppler is available, it may diagnose probable adnexal/ovarian torsion by demonstrating an enlarged ovary with absent blood flow compared with the opposite adnexa. However, two arterial sources supply the ovary, the ovarian and the uterine arteries, so normal blood flow does not exclude ovarian torsion. A torsioned cyst is often associated with a torsioned ovary, and may have a fluid–fluid level and a thickened rim of tissue, and be tender with palpation with the transvaginal probe. Urolithiasis is discussed in a separate section of this chapter.

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