DFT-17/09/2025-ANATOMY D3

A 45-year-old chef sustains a penetrating injury from a thin metal skewer to the right side of his neck at the C6 level. His neurological examination reveals a selective loss of pain and temperature sensation in the C6 dermatome on the right side. However, his perception of light touch, vibration, and proprioception in the same dermatome remains completely intact. Motor function is also unaffected. Which of the following structures is most likely selectively damaged?

• Substantia gelatinosa at C6

• Fasciculus cuneatus at C6

• Dorsal root ganglion at C6

• Anterior horn at C6

Answer explanation

The substantia gelatinosa (Rexed lamina II) is the primary site where first-order neurons carrying pain and temperature information synapse. A focal lesion here would produce an ipsilateral, segmental loss of these modalities, matching the patient's dissociated sensory loss.

A 68-year-old male with a history of severe atherosclerosis presents to the emergency department with an acute onset of flaccid paralysis of his left lower limb and a complete loss of pain and temperature sensation in his right lower limb below the T10 dermatome. Examination reveals intact proprioception, vibration, and light touch sensation in both lower limbs. Which of the following vascular territories is most likely compromised?

• Left Anterior Spinal Artery at T9

• Right Posterior Spinal Artery at T9

• Artery of Adamkiewicz at T10

• Left Dorsal Root Ganglion at L2

Answer explanation

The anterior spinal artery supplies the anterior two-thirds of the cord, including the corticospinal and spinothalamic tracts. A unilateral occlusion explains the ipsilateral motor loss (corticospinal) and contralateral pain/temperature loss (spinothalamic tract, which decussates).

Among the cranial nerves depicted in the provided anatomical specimen, which one is exclusively composed of General Somatic Efferent (GSE) fibers that innervate musculature derived from the occipital somites?

•  Hypoglossal nerve (CN XII)

•  Oculomotor nerve (CN III)

• Trigeminal nerve (CN V)

• Vagus nerve (CN X)

Answer explanation

The hypoglossal nerve (CN XII) is a pure motor nerve (GSE) that innervates the intrinsic and extrinsic muscles of the tongue, which embryologically originate from the occipital somites.

A 58-year-old male with metastatic lung cancer is undergoing cisplatin-based chemotherapy. He develops intractable nausea and vomiting shortly after the infusion. Which of the following structures, located on the floor of the fourth ventricle, is primarily responsible for mediating this emetic response?

• Area postrema

• Medial longitudinal fasciculus

• Facial colliculus

• Superior colliculus

Answer explanation

The area postrema contains the chemoreceptor trigger zone (CTZ). It is a circumventricular organ with a fenestrated capillary network, lacking a true blood-brain barrier, allowing it to detect emetogenic substances like cisplatin in the blood.

A 62-year-old male with a history of nasopharyngeal carcinoma presents with a persistent headache, diplopia on left lateral gaze, and numbness over his left cheek and upper lip. On examination, he has an isolated left-sided abducens nerve palsy and sensory loss in the distribution of the maxillary division of the trigeminal nerve. Which of the following foramina is the most likely location for a lesion causing this specific constellation of symptoms?

• Superior orbital fissure

• Foramen rotundum

• Jugular foramen

•  Foramen ovale

Answer explanation

The superior orbital fissure transmits the abducens nerve (CN VI) and the ophthalmic division (V1) of the trigeminal nerve. A lesion here can affect CN VI, but its proximity to the foramen rotundum allows a single pathology to affect both CN VI and V2.

Which of the following cranial nerves is unique in that its motor nucleus is located in the midbrain, yet its fibers emerge from the dorsal aspect of the brainstem before traversing the superior orbital fissure?

• Trochlear nerve (IV)

  
  

• Oculomotor nerve (III)

  
  

• Abducens nerve (VI)

•  Facial nerve (VII)

Answer explanation

The trochlear nerve is the only cranial nerve that exits from the dorsal aspect of the brainstem. Its nucleus is in the midbrain at the inferior colliculus level.

A 65-year-old woman with poorly controlled hypertension presents with an acute onset of left-sided paralysis. On examination, there is left hemiparesis (0/5 power), complete loss of vibratory and position sense on the left side, and the protruded tongue deviates to the right. Pain and temperature sensation are intact bilaterally. Which numbered transverse section in the provided diagram most accurately corresponds to the anatomical location of the infarct?

• Section 4

• Section 3

• Section 7

• Section 2

Answer explanation

This clinical triad—contralateral hemiparesis (pyramidal tract), contralateral loss of proprioception (medial lemniscus), and ipsilateral tongue deviation (hypoglossal nucleus/nerve)—is characteristic of Medial Medullary Syndrome (Dejerine's syndrome), which localizes to the level shown in Section 4.

A 72-year-old male with a history of poorly controlled hypertension and atrial fibrillation is brought to the emergency department after his wife noted an abrupt change in his status. On examination, he has profound weakness (0/5 strength) and sensory loss in his right lower extremity. His right upper extremity and facial strength are preserved (5/5). He also developed urinary incontinence. Which of the following vascular occlusions best explains this clinical presentation?

• Left Anterior Cerebral Artery

• Left Middle Cerebral Artery

•  Left Posterior Cerebral Artery

• Basilar Artery

Answer explanation

This presentation is classic for an Anterior Cerebral Artery (ACA) stroke. The ACA supplies the medial portion of the frontal and parietal lobes, where the motor and sensory cortices for the contralateral leg and foot are located, along with the paracentral lobule which influences bladder control.

A 55-year-old male with a history of uncontrolled hypertension and polycystic kidney disease is brought to the emergency department after collapsing. He had complained of a sudden, explosive "thunderclap" headache. On examination, he has nuchal rigidity and a distinct bitemporal hemianopia. A non-contrast CT head confirms diffuse subarachnoid hemorrhage, most prominent in the suprasellar cistern. Which vessel is the most likely source of the hemorrhage?

• Anterior communicating artery

• Posterior communicating artery

• Middle cerebral artery bifurcation

•  Basilar artery tip

Answer explanation

Aneurysmal rupture of the anterior communicating artery, a common site for berry aneurysms, leads to subarachnoid hemorrhage. Its strategic location superior to the optic chiasm explains the compression causing bitemporal hemianopia.

A 62-year-old right-handed male is evaluated for a sudden onset of speech difficulty. He is fluent and his comprehension is intact, but he demonstrates significant trouble with repeating phrases (e.g., "no ifs, ands, or buts"). He also exhibits mild ideomotor apraxia with his right hand. A neurological examination reveals no significant motor weakness, sensory loss, or visual field deficits. Based on this presentation, which type of white matter tract is most likely affected?

•  Association fibers

• Commissural fibers

• Projection fibers

• Stria medullaris thalami

Answer explanation

The clinical picture of conduction aphasia (fluent speech, intact comprehension, poor repetition) with ideomotor apraxia points to a lesion in the arcuate fasciculus, a major association fiber tract connecting Wernicke's and Broca's areas.