Anatomy Flashcards

A patient presents with inability to abduct the arm beyond 15° and loss of sensation over the deltoid region. Imaging reveals a fracture of the surgical neck of the humerus. Which nerve is most likely injured, and through which foramen does it pass to reach its target muscle?

Answer: Axillary nerve; passes through the quadrangular space

The axillary nerve winds around the surgical neck of the humerus and passes through the quadrangular space (bounded by teres minor, teres major, long head of triceps, and humerus). It innervates the deltoid and teres minor, and its cutaneous branch supplies the 'regimental badge' area over the deltoid. Loss beyond 15° abduction (supraspinatus handles the first 15°) is characteristic of deltoid paralysis.

During a posterior mediastinal dissection, a surgeon identifies a structure that crosses the midline at the level of T8 vertebra, pierces the diaphragm through its own opening rather than through a designated hiatus shared with other structures, and carries parasympathetic fibers to abdominal viscera. What is this structure?

Answer: Right vagus nerve forming the posterior vagal trunk

The esophagus passes through the diaphragm at T10 accompanied by the vagal trunks. However, the right vagus nerve rotates posteriorly during gut rotation to form the posterior vagal trunk, which carries parasympathetics to abdominal viscera. The esophagus pierces the diaphragm at T10; the vena cava at T8; the aorta at T12. The posterior vagal trunk (predominantly right vagus) travels with the esophagus but functionally the right vagus is the key parasympathetic contributor to the posterior trunk.

A 45-year-old man undergoes a radical parotidectomy. Postoperatively he develops Frey syndrome — gustatory sweating over the preauricular skin when eating. Which embryological misrouting best explains this phenomenon?

Answer: Aberrant regeneration of the auriculotemporal nerve fibers into sympathetic sweat gland pathways

Frey syndrome results when postganglionic parasympathetic secretomotor fibers (originally destined for the parotid gland via the auriculotemporal nerve from the otic ganglion) aberrantly reinnervate the sweat glands and cutaneous vasculature of the preauricular skin, which are normally under sympathetic control. Eating stimulates parasympathetic activity that now triggers sweating rather than salivation.

The coronary sinus drains into the right atrium between the right atrioventricular orifice and the inferior vena cava orifice, guarded by the valve of the coronary sinus. Which of the following veins does NOT drain into the coronary sinus under normal anatomical conditions?

Answer: Anterior cardiac veins

The anterior cardiac veins (right marginal and anterior right ventricular veins) bypass the coronary sinus entirely and drain directly into the right atrium. The great cardiac vein, middle cardiac vein, small cardiac vein, posterior vein of the left ventricle, and the oblique vein of the left atrium (vein of Marshall) all drain into the coronary sinus.

A surgeon performing a posterior approach to the hip joint must identify the short external rotators to avoid injury to the sciatic nerve. Which of the following correctly identifies the nerve supply AND the relationship of the sciatic nerve to the piriformis muscle in the most common anatomical variant?

Answer: Piriformis is supplied by S1–S2 nerve roots; sciatic nerve exits below piriformis as a single trunk

In approximately 85% of individuals (the most common variant), the sciatic nerve exits as a single trunk inferior to the piriformis muscle through the greater sciatic foramen. Piriformis itself is innervated by direct branches from the ventral rami of S1 and S2. The variant where the common fibular (peroneal) division pierces piriformis (Beaton & Anson type B) occurs in ~10% and is a cause of piriformis syndrome.

During a thyroidectomy, the surgeon must identify the recurrent laryngeal nerve (RLN) before ligating the inferior thyroid artery. Which statement most accurately describes the anatomical relationship that makes the right RLN more vulnerable to injury than the left during thyroid surgery?

Answer: The right RLN follows a more oblique, lateral course and enters the larynx at a less predictable angle relative to Berry's ligament

The right RLN loops under the right subclavian artery and follows a more oblique and lateral course toward the larynx, making it less predictably located in the tracheoesophageal groove and more variable in its relationship to the inferior thyroid artery and Berry's ligament. The left RLN loops around the aortic arch and ascends more consistently in the tracheoesophageal groove, making it easier to identify. Importantly, a nonrecurrent RLN (~1%) occurs on the RIGHT (not left) due to aberrant right subclavian artery (arteria lusoria), but this is a separate, additional vulnerability.