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
RibsIntercostal spaceIntercostal neurovascular bundleMediastinumPneumothorax1.
All of the following are correct except
(a)
The ribs, sternum, and intercostal musculature arise from the mesoderm.
(b)
The ribs develop from processes arising from the sternum.
(c)
The sternum develops from two independent ventral mesenchymal condensations known as sternal bars.
(d)
The sternal bars are originally paired, but later in development they “zipper” together in craniocaudal direction.
(e)
Complete rib ossification is achieved at age 20–25.
Comments
The muscular and bony elements of the thoracic wall are of mesodermal origin. The ribs arise from the vertebra and extend to the anterior midline following a curvilinear course, joining the sternum through costal cartilages. Anomalies of this developmental process are thought to be the cause of pectus excavatum, which is the most common chest wall deformity (1:400 children).
The sternum is derived from paired sternal bars in the anterior midline. These structures fuse in craniocaudal direction and articulate with the first seven ribs. When this process fails to occur, the separation left in the anterior midline creates aesthetic deformity (bifid sternum) and may allow herniation of the mediastinal structures as well as of the lungs. Association of this pathology with cardiac anomalies has been reported [1, 2].
Answer
b
2.
The angle of Louis, corresponding to T4–T5, marks the following except:
(a)
Division of the mediastinum into superior and inferior
(b)
Beginning and end of the aortic arch
(c)
Bifurcation of the trachea
(d)
Origin of the superior vena cava
(e)
Positioning of the thoracic duct to the right of the spine
Comments
The angle of Louis represents the junction of the sternal manubrium and sternal body. It is a key landmark in thoracic anatomy. While it is true that the thoracic duct starts to the right of the spine at its origin in the cisterna chyli, it crosses the midline towards the left starting at T6 level, to reach the left subclavian vein [3] (Fig. 2.1).
Fig. 2.1
Angle of Louis. Pierre-Charles-Alexandre Louis, a nineteenth century French physician, was of the first to bring mathematics to medicine. The angle of Louis is approximately 162° in males and marks a plane from the second costal cartilage to the lower border of T4 vertebra posteriorly. This is an important anatomical landmark in the chest and represents division of the superior from the inferior mediastinum
Answer
e
3.
All of the following are correct except:
(a)
The ribs are classified into seven true ribs, five false ribs, and two floating ribs.
(b)
The ribs are staggered between the thoracic vertebrae, articulating with two of them at the same time, superiorly and inferiorly.
(c)
Cervical ribs are found in 1 % of the population, causing symptoms in 10 % of affected individuals.
(d)
The costal groove, running along the inferior border of the rib, contains intercostal neurovascular bundle.
(e)
In the newborn, the intercostal muscles play a key role during breathing.
Comments
Ribs are classified into three categories. True ribs are joined to the sternum by the costal cartilages. False ribs are joined to superior ribs by cartilages that in conjunction form the costal arch. Floating ribs do not articulate anteriorly, but are stabilized by the intercostal muscles. In adults, the ribs are placed in a fashion similar to bucket handles, where upon contraction of the intercostals muscles, they are pulled superiorly and anteriorly increasing the diameter of the thoracic cavity and contributing to the negative intrathoracic pressure resulting in inspiration. In contrast, newborns exhibit a nearly horizontal orientation of the ribs. They are unable to generate further radial expansion of the thoracic cavity and rely on craniocaudal expansion through diaphragmatic action for ventilation [4].
The relationship of the intercostal neurovascular bundle to the rib largely dictates the technique for tube thoracostomy and intercostal blocks. Given that the bundle runs along the lower margin of the rib, it is safest to access the pleural cavity along the upper margin of the rib, thus avoiding vascular laceration and subsequent bleeding [5] (Fig. 2.2).
Fig. 2.2
Tube thoracostomy. A chest tube (tube thoracostomy) is typically inserted to drain air or fluid from the pleural cavity. The safest point of entry into the chest cavity is just above the upper border of a rib in the intercostal space. In this location, there is the least chance of injury to the neurovascular bundle. For fluid drainage, a chest tube is inserted laterally near the anterior axillary line and in the safest lower intercostal space for dependent drainage
The elements of the neurovascular bundle are arranged with the vein in cranial position, the nerve in caudal position, and the artery in between. They originate posteriorly, at a level more caudal than that of the inferior border of the rib and thus follow an ascending diagonal course towards the rib, making them more accessible posteriorly for an intercostal block. Once they join the rib, they follow a discretely spiral course towards the inferior inner margin of the rib. The neurovascular bundle is deep to the intercostal muscles and immediately adjacent to the pleura [6] (Fig. 2.3).
