Anatomy Flashcards

A surgeon performing a posterior cervical dissection inadvertently damages the nerve that travels through the posterior triangle of the neck, crosses the middle scalene muscle, and provides sensation to the skin overlying the upper thorax and shoulder. Which nerve was injured?

Answer: Supraclavicular nerve

The supraclavicular nerve (C3–C4) is a branch of the cervical plexus that crosses the posterior triangle, passes over the clavicle, and provides cutaneous innervation to the skin of the upper thorax, shoulder cap, and clavicular region. The suprascapular nerve is a motor/sensory nerve to the supraspinatus and infraspinatus muscles and does not cross the posterior cervical triangle in this manner. The intercostobrachial and medial cutaneous nerves arise from the brachial plexus and supply the upper arm.

During a cadaveric dissection of the hand, a student notes that a small muscle originates from the hook of the hamate and the flexor retinaculum, and inserts into the medial border of the fifth metacarpal. Paralysis of this muscle would most impair which movement?

Answer: Abduction of the little finger

The muscle described — originating from the hook of the hamate and flexor retinaculum and inserting into the medial border of the fifth metacarpal — is the abductor digiti minimi. It is the prime mover for little finger abduction at the MCP joint. The opponens digiti minimi (also from the hamate) inserts along the shaft of the fifth metacarpal to produce opposition. Flexor digiti minimi brevis flexes the proximal phalanx. Adduction is produced by the palmar interossei.

A 45-year-old patient presents with a cavernous sinus thrombosis. Which of the following cranial nerves would be LAST to be affected as pressure within the sinus progressively increases from lateral wall compression inward?

Answer: Abducens nerve (CN VI)

The lateral wall of the cavernous sinus, from superior to inferior, contains CN III, CN IV, CN V1, and CN V2 embedded within the dural layers. The abducens nerve (CN VI) runs freely through the interior of the sinus alongside the internal carotid artery, making it the most exposed to early pressure effects from elevated intra-sinus pressure. However, because CN VI lies in the center of the sinus rather than the lateral wall, it is paradoxically often affected EARLY by thrombosis. The lateral wall nerves (III, IV, V1) are compressed progressively as the sinus expands outward — V2 is the most inferolateral and would typically be affected last among the lateral wall nerves. CN VI, being centrally placed, is not 'last' — CN V2 (not listed) would be last of the lateral wall nerves. Among the options given, CN VI is most centrally placed and is paradoxically affected early rather than last, making it the outlier; CN V1 is the most inferolateral of the listed lateral wall nerves and would be compressed last among this set.

A radiologist reviewing a cross-sectional CT at the level of the T8 vertebral body identifies a structure passing through the diaphragm at this level. Which structure is correctly matched to the T8 vertebral level?

Answer: Inferior vena cava

The inferior vena cava (IVC) passes through the caval foramen in the central tendon of the diaphragm at the T8 vertebral level, accompanied by the right phrenic nerve. The esophagus, along with the vagal trunks, passes through the esophageal hiatus at T10. The aorta passes through the aortic hiatus at T12, accompanied by the thoracic duct and azygos vein. A common mnemonic is 'I 8 (ate) 10 eggs at 12' — IVC at T8, Esophagus at T10, Aorta at T12.

A neurosurgeon ligates the posterior inferior cerebellar artery (PICA) proximal to its branching point during a posterior fossa procedure. Which nucleus within the medulla would most likely be directly infarcted?

Answer: Nucleus ambiguus

Occlusion of the PICA produces the lateral medullary (Wallenberg) syndrome, affecting the lateral medulla. The nucleus ambiguus lies in the lateral medullary tegmentum and contains lower motor neurons for the glossopharyngeal (CN IX), vagus (CN X), and accessory (CN XI) nerves, producing dysphagia and hoarseness. The hypoglossal nucleus and nucleus gracilis are located in the medial and posterior medulla respectively, supplied by anterior spinal and posterior spinal artery territories, not PICA. The dorsal motor nucleus of the vagus lies medially near the floor of the fourth ventricle and is also spared in pure lateral medullary infarcts.

A trauma patient sustains a penetrating injury to the right gluteal region at the level of the piriformis muscle. The patient subsequently exhibits weakness in abduction and medial rotation of the hip, along with sensory loss over the anterolateral thigh. Which nerve was most likely injured?

Answer: Superior gluteal nerve

The superior gluteal nerve (L4–S1) exits the greater sciatic foramen above the piriformis muscle and runs between the gluteus medius and minimus, innervating both muscles along with the tensor fasciae latae. Gluteus medius and minimus are the primary abductors and medial rotators of the hip. The tensor fasciae latae also contributes to medial rotation and provides the lateral femoral cutaneous sensation via the iliotibial band territory. The inferior gluteal nerve (below piriformis) innervates gluteus maximus (extension). The sciatic nerve exits below piriformis and does not produce isolated hip abduction/medial rotation weakness with anterolateral thigh sensory loss. The posterior femoral cutaneous nerve provides posterior thigh sensation only.