and Edgar D. Guzman-Arrieta3
(1)
Department of Surgery Advocate Illinois Masonic Medical Center, University of Illinois Metropolitan Group Hospitals Residency in General Surgery, Chicago, IL, USA
(2)
University of Illinois at Chicago, Chicago, IL, USA
(3)
Vascular Specialists – Hattiesburg Clinic, Hattiesburg, MS, USA
Keywords
NeckPharyngeal embryologyThyroid glandParathyroid glandThoracic outlet syndrome1.
All of the following are correct except:
(a)
The pharyngeal arches are of mesodermal origin.
(b)
The pharyngeal pouches are of endodermal origin.
(c)
The foramen cecum and middle part of the thyroid are of mesodermal origin.
(d)
The branchial membranes bridge the spaces between the pharyngeal arches.
(e)
The superior parathyroids and thyroid share a common origin.
Comments
The human branchial apparatus is analogous to the gills found in fish. As mammals developed lungs for breathing, gills lost their respiratory function. However, the branchial apparatus continued to contribute to the formation of head and neck structures. Congenital anomalies of these areas in humans give rise to branchial sinuses, cysts, and other defects (Fig. 1.1). By the fifth week of gestation, only 4 branchial clefts are visible in the human embryos.
Fig. 1.1
The human embryonic pharynx consists of six paired branchial arches lined by ectodermal clefts and endodermal pouches around an unpaired endodermal ventral floor. Each of these structures forms parts of the face and neck. As these structures develop, overhang, and fuse; the adult components of the face and neck are formed. Embryologic developmental errors in this process present as sinuses, fistulae, cysts, aberrant locations and/or the absence of organs in the face and neck. Many of the anomalies covered in this chapter present a unique set of anatomical relationships which become clinically relevant for their diagnosis and treatment. The very thin membrane that exists between clefts and pouches, phylogenetically representing the gills, has no function in humans
The isthmus of the thyroid along with the pyramidal lobe and the anteromedial thyroid lobes is formed by an endodermal extension of the foramen cecum of the tongue, which descends through the hyoid bone. The lateral and posterior aspects of the thyroid lobes develop along with the superior parathyroids from the fourth branchial pouch. Hence, when a superior parathyroid cannot be found, an intrathyroidal location must be confirmed and at times requires ipsilateral thyroid lobectomy. In similar fashion, when an inferior parathyroid cannot be located, an intrathymic location should be suspected, considering the common origin of these two structures in the third pharyngeal pouch.
Answer
c
2.
All of the following are correct except
(a)
The first pharyngeal arch, responsible for the embryogenesis of the muscles of mastication, is innervated by the mandibular branch of the trigeminal nerve and its blood supply is from the facial artery.
(b)
The second pharyngeal arch, responsible for the embryogenesis of the muscles of facial expression, is innervated by the facial nerve and its artery is the external carotid.
(c)
The second pharyngeal pouch gives rise to the tonsils. The second pharyngeal pouch sinuses open into the tonsillar fossa.
(d)
The third pharyngeal pouch is responsible for the formation of the upper parathyroids.
(e)
The fourth pharyngeal arch is responsible for the embryogenesis of the cricothyroid muscle and its nerve supply is through the superior laryngeal branch of the vagus nerve.
Comments
The pharyngeal arches are responsible for the mesodermal derivatives of the lower face and neck. Pharyngeal pouches give rise to endodermal elements. Pharyngeal clefts are ectodermal. Only the first cleft persists into adulthood, forming the external auditory canal. In correspondence, the first pharyngeal pouch forms the middle ear. The first pharyngeal cleft may give rise to a persistent preauricular sinus or cyst which courses anterior to the facial nerve towards the external auditory canal.
Most branchial fistulae and cysts originate from the second pharyngeal pouch and cleft. Classically, these fistulae open at the lower third of the medial border of the sternocleidomastoid muscle. These sinus or fistulae typically travel from the tonsillar fossa coursing in between the internal and external carotid arteries to reach the skin (Fig. 1.2).
Fig. 1.2
A second branchial fistula typically extends from an external opening in the lower third of the neck, anterior to the sternocleidomastoid muscle. The fistula extends through the bifurcation of the carotid to an internal opening in the tonsillar fossa. Multiple variations exist when the fistula is not complete
The third pharyngeal pouch is responsible for the genesis of the inferior parathyroids and thymus. It is interesting to note that the upper parathyroids and thyroid develop from the fourth pharyngeal pouch, while the lower parathyroid and thymus develop from the higher third pharyngeal pouch and migrate caudally [1].
Answer
d
3.
Select the incorrect statement regarding the embryology of the thyroid.
(a)
The median thyroid anlage is derived from the pharyngeal floor and is of endodermal origin. It forms the follicular component of the thyroid.
(b)
The lingual thyroid does not have C cells.
(c)
The thyroglossal duct is posterior to the hyoid bone and does not involve it.
(d)
The C cells of the thyroid come from the ultimobranchial bodies.
(e)
The neural crest origin of the C cells of the thyroid explains the association of medullary cancer with other neuroendocrine malignancies.
Comments
As discussed in question 1, the follicular elements of the thyroid are of endodermal origin. The middle thyroid anlage descends from the base of the tongue following a trajectory anterior to or through the hyoid bone. The lateral thyroid anlagen are derived from the fourth branchial pouches. The C cells of the thyroid gland are derived from the ultimobranchial body, which is a part of the fourth branchial pouch that is colonized by neuroectodermal cells. They are confined to the lateral aspects of the thyroid.
C cells may give rise to medullary thyroid carcinoma. Reflecting the function of the parent cells, medullary carcinomas may produce calcitonin. This hormone is a useful tumor marker (Fig. 1.3).
Fig. 1.3
The median thyroid anlage forms all of the follicular thyroid. All differentiated thyroid neoplasms arise from this embryonic origin of the thyroid. The paired lateral anlage arise from the fourth and fifth branchial pouches and fuse with the median anlage. Calcitonin-secreting parafollicular cells, also called C cells, migrate into the lateral anlage from neuroectoderm. C cells disperse in the superior and lateral part of the thyroid and are the parent cells for medullary carcinoma of the thyroid. Thyroid neoplasms maintain many of the characteristics of their embryological cell of origin. For example, papillary carcinoma traps radioactive iodine, and medullary carcinoma over-expresses the RET protein which is derived from embryonic nervous tissue
Medullary carcinoma of the thyroid may be an isolated familial disease or a component of type 2 multiple endocrine neoplasia (MEN-2) syndromes, together with pheochromocytomas and parathyroid hyperplasia (MEN-2a) or neuromas and marfanoid body habitus (MEN-2b). The underlying theme in these neoplasias is their neuroectodermal origin. This is further substantiated by the pervasive involvement of the RET proto-oncogene.
The RET proto-oncogene is a receptor linked to a tyrosine kinase, normally present in neuroectodermal-derived cells. Mutations leading to its pathologic activation lead to sustained growth signals and tumor development. Interestingly, loss of function mutations of the RET proto-oncogene has been associated with Hirschsprung’s disease. In this instance, there is failure of development of the Auerbach’s plexus, also derived from the neuroectoderm [2].
Answer
c
4.
Select the correct statement regarding neck surgery.
(a)
The strap muscles are best divided below their upper third to prevent undue denervation.
(b)
A vertical incision in the anterior triangle can be safely extended to the angle of the mandible.
(c)
Vertical incisions provide better cosmetic results.
(d)
Flap creation should be carried along a plane superficial to the platysma muscle.
(e)
The section of the anterior cervical branch of the facial nerve causes permanent drooling.
Comments
The innervation of the strap muscles (sternohyoid and sternothyroid) is provided by the ansa cervicalis. The branches of the ansa cervicalis approach these muscles from below; hence, section of the muscle in its lower aspect interrupts the innervation to the majority of the muscle, whereas a cephalad division preserves it. The ansa cervicalis has a unique looping pattern, uniting C1 with C2 and C3 root elements. It may be traced back to the hypoglossal nerve and as such can be a useful anatomical landmark in carotid surgery. On occasion, its presence may impede access to the carotid artery. In this instance, it may be divided without significant consequence (Fig. 1.4).
Fig. 1.4
The ansa cervicalis is the handle, or loop, of a nerve connecting C1 fibers from the descendens hypoglossi nerve to the contributions from the C2 and C3 spinal nerves. This loop provides nerve supply to the sternohyoid and sternothyroid muscles, and contributes to the omohyoid
The mandibular branch of the facial nerve and the anterior ramus of the cervical branch of the facial nerve follow a hammock-like course bellow the angle of the mandible. This exposes them to injury when incisions are made within a 3 cm radius of this landmark (Fig. 1.5).
Fig. 1.5
The marginal mandibular branch of the facial nerve is an important nerve for smiling and other facial expressions with the lips. It has multiple variations in branching. To avoid injury to this nerve, a skin incision 3 cm. below the angle of mandible followed by careful dissection of the subplatysmal skin flaps is necessary
Injury to the mandibular branch of the facial nerve results in paralysis of the orbicularis oris, producing permanent drooping of the corner of the mouth and drooling. Injury to the anterior cervical branch of the facial nerve produces transient drooling.
Vertical incisions are to be avoided in the neck for cosmetic reasons. Preferably horizontally oriented curvilinear incisions along Langer’s lines should be used. All flaps in the neck should be made in the avascular plane deep to the platysma, as the platysma is actually attached to the skin of the neck. The platysma is a remnant of the subcutaneous muscle seen in the animals which can move their skin to ward off insects and birds.
Answer
a
5.
Select the incorrect statement regarding Ludwig’s angina causing respiratory distress.
(a)
Incision and drainage is the first therapeutic maneuver.
(b)
The sublingual and submaxillary spaces communicate posteriorly around the mylohyoid muscle.
(c)
Infection can extend to the pharyngomaxillary and retropharyngeal spaces requiring urgent awake tracheostomy.
(d)
The main sources of infection in Ludwig’s angina are the lower molars.
(e)
Streptococcus hemolyticus is the chief microorganism involved.
Comments
The most important intervention in the treatment of Ludwig’s angina causing respiratory distress is to secure the airway. This is best done through awake tracheostomy after initiation of gastric acid suppression and cholinergic blockade. Attempts at nasotracheal and orotracheal intubation, with or without bronchoscopic guidance, are likely to fail due to severe anatomic distortion. This same factor makes emergent cricothyroidotomy likely to be unsuccessful [3, 4].
Answer
a
6.
Select the incorrect statement regarding the carotid sinus and body.
(a)
The carotid sinus is innervated by the glossopharyngeal nerve.
(b)
Carotid sinus distention triggers an elevation of the heart rate and blood pressure.
(c)
The carotid body is located at the carotid bifurcation.
(d)
The carotid body triggers hyperventilation when exposed to high hydrogen ion concentrations.
(e)
Tumors of the carotid body (chemodectomas) are highly vascular.
Comments
The carotid sinus and body are often confused as one structure. They are distinct and fulfill separate functions important in regulating nutrient delivery to the brain.
The carotid sinus is a baroreceptor located in the dilated origin of the internal carotid artery. It controls blood flow by decreasing cardiac output when its walls are stretched. This is accomplished by the generation of a vagal reflex (baroreceptor reflex), which can also be triggered by manipulation of this structure in the course of carotid surgery or stenting. The baroreceptor reflex is not to be confused with the Bainbridge reflex, which is triggered by atrial distention, inducing an increase in heart rate.
The carotid body is a chemoreceptor sensitive to low pH and oxygen tension as well as increased carbon dioxide concentration. When stimulated it induces an increase in ventilation to return these parameters to normal levels.
The carotid body originates from the third branchial arch mesoderm and cells of neural crest origin. It is located within the adventitia of the carotid bifurcation. It is innervated by the glossopharyngeal nerve and closely related to the superior laryngeal nerve as well as the hypoglossal nerve. Tumors originating from this structure are very vascular, contraindicating needle biopsies [5].
Answer
b
7.
Select the correct statement regarding the thoracic outlet.
(a)
The subclavian artery and the brachial plexus course between the posterior and middle scalene.
(b)
Accessory cervical ribs (C7) are a common cause of compression of the subclavian vein.
(c)
Paget–Schroetter syndrome consists of the effort-related thrombosis of the subclavian artery.
(d)
Poststenotic dilatations of the subclavian artery are associated with thrombi formation.
(e)
Anterior scalenectomy has no role in the treatment of thoracic outlet syndrome.
Comments
Nomenclature pertaining the thoracic outlet and inlet can be confusing. From a strictly anatomical perspective, the thoracic outlet is the lower border of the rib cage, covered by the diaphragm. In turn, the thoracic inlet is defined as the opening bound by the manubrium, the upper border of T1 and the first rib.
From a clinical perspective, the term thoracic outlet is defined by the passage of the neurovascular elements to the upper extremity. Instead of consisting of a bidimensional ringlike plane, the clinical thoracic outlet is a wedge-shaped volume, occupying the space between the first rib and the clavicle [6] (Fig. 1.6).
Fig. 1.6
Terminology of the thoracic inlet and outlet is often confusing. We recommend describing the anatomy as follows: the thorax has a single bony inlet bounded by the manubrium anteriorly, the first rib laterally, and the C7–T1 vertebrae posteriorly. The thorax has two outlets, an inferior outlet bounded by the diaphragm, leading to the abdomen, and a superior outlet to the upper extremity bounded by the clavicle and the first rib
The thoracic outlet has three areas of potential compression:
1.
The costoclavicular space, between the first rib and the clavicle (partially covered by the subclavius muscle).
2.
The interscalene triangle, bound by the first rib inferiorly, the anterior scalene anteriorly, and the middle scalene posteriorly. It contains the subclavian artery and brachial plexus.
3.
The subcoracoid space, underneath the pectoralis minor tendon. This muscle marks the transition into the axillary space.
Both the subclavian vein and artery cross over the first rib as they exit the thorax. The subclavian vein courses anterior to the anterior scalene muscle. The subclavian artery crosses behind this muscle, but anterior to the middle scalene muscle, in the space previously defined as the interscalene triangle. Here, it is joined by the elements of the brachial plexus that course in a more superior and slightly more posterior path (Fig. 1.7).
Fig. 1.7
The thoracic outlet is the tight space between the clavicle and the first rib traversed by scalene muscles. The subclavian artery and the brachial plexus are between the scalenus anterior and medius muscles, while the subclavian vein is anterior to the scalenus anterior in the tightest space
The subclavian vein may be compressed between the first rib, clavicle, and anterior scalene muscle. More laterally, the subclavius muscle may also cause compression against the chest wall. Paget–Schroetter syndrome is effort-related subclavian vein thrombosis caused by repeated strenuous overhead activity, classically, of the dominant arm (Fig. 1.8).
Fig. 1.8
Repetitive strenuous trauma in the tight space between the clavicle and the first rib is the key factor in subclavian–axillary vein thrombosis, also referred to as effort thrombosis or Paget–Schroetter syndrome. Baseball pitchers, manual “jackhammer” operators, swimmers, and other professionals with activities producing this repetitive microtrauma to the subclavian vein endothelium are at higher risk
The subclavian artery and brachial plexus can be compressed within the interscalene triangle, bringing about the vascular and neurological manifestations of the thoracic outlet syndrome. This is more likely in the presence of anomalous bands of muscle and tendon or an accessory cervical rib (Fig. 1.9).
Fig. 1.9
Presence of an accessory cervical rib, as shown above, may significantly narrow the thoracic outlet causing narrowing of the subclavian artery. Resultant poststenotic dilatation can add to the problem with embolic disease. Common associated neurologic problems are compression of C8 and T1
Cervical ribs arise from the transverse process of C7 and follow a course that parallels that of the first rib. Cervical ribs may reach the sternum, but more frequently terminate in a ligamentous structure that attaches to the upper margin of the first rib. This ligament may exert compression over the elements of the brachial plexus [7] (Fig. 1.10).
Fig. 1.10
The cervical ribs are seen in about 1 % of the population, are often bilateral, are more common on the left and have three times higher incidence in women. Their extent can be anywhere from a long transverse process of the C7 vertebra to a complete rib inserting on the manubrium. The vast majority are asymptomatic, but the accessory ribs are one of the established causes of the thoracic outlet syndrome causing compression of the lower cord of the brachial plexus and subclavian artery
Answer
d
8.
Mark the incorrect statement regarding the spaces of the neck and their pathology.
(a)
Retropharyngeal abscesses occur between the prevertebral fascia and the posterolateral wall of the pharynx.
(b)
The retropharyngeal abscesses are acute in nature, secondary to regional infections, esophageal perforations, and pathology of the deep cervical nodes.
(c)
Abscesses between the vertebral bodies and the prevertebral fascia are of chronic nature, secondary to vertebral osteomyelitis.
(d)
The axillary fascia takes origin in the prevertebral fascia and extends along the brachial artery, allowing the extension of vertebral osteomyelitis into the arm.
(e)
The pretracheal space is not a route of dissemination of cervical pathology into the mediastinum.
Comments
The vascular and nerve structures that course through the neck do so enveloped in sheaths that extend into the head, thorax, and upper extremities, creating pathways for the dissemination of infections.
The prevertebral fascia serves as a landmark for deep soft tissue infections in the neck. The retropharyngeal space lies anterior to it, extending from the base of the skull to the mediastinum. In turn, the prevertebral space is posterior to the prevertebral fascia, with the cervical vertebrae serving as a posterior border. This space extends into the upper arm along the axillary sheath (Fig. 1.11).
Fig. 1.11
The prevertebral space continues into the arm with the axillary vessels and brachial plexus. The retropharyngeal space may continue into the mediastinum or carotid sheath
Retropharyngeal abscesses have the potential to become life threatening due to airway obstruction, involvement of the carotid sheath, spread into the mediastinum, and septic shock. Mortality rate for this pathology is as high as 50 %. Contamination of this space usually arises from the pharynx, secondary to trauma, foreign bodies, and upper respiratory infections. Children less than 5 years of age are the most affected, but currently, there is an increasing incidence among immunocompromised adults [8, 9].
Prevertebral abscesses are more commonly chronic in nature. The vertebrae themselves are most often the source of contamination, although this space may be seeded during spinal surgery as well [10].
The pretracheal space extends into the middle mediastinum, ending at the pericardium. This space is developed during mediastinoscopy, a procedure that does not confer access to the anterior or posterior mediastinum.
Answer
e
9.
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Regarding the surgical management of vascular injuries in the neck, all of the following are correct except:
(a)
The external jugular vein can be ligated if the internal jugulars are intact.
(b)
The internal jugular vein may be ligated unilaterally.
(c)
The external carotid artery can be safely ligated.
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