Normal Neuroanatomy: The Scaffold for Every Diagnosis
Why anatomy drives neuropathology questions
Most missed items on this exam are not histology failures but localization failures. You must be able to move fluently between gross landmarks, vascular territories, and microscopic architecture.
Core concepts to master:
- Lobar and deep gray anatomy: frontal, parietal, temporal, occipital, insula; basal ganglia (caudate, putamen, globus pallidus), thalamus, subthalamic nucleus, internal capsule somatotopy.
- Vascular territories: ACA (medial surface, leg weakness), MCA (lateral convexity, face/arm), PCA (occipital, thalamus), vertebrobasilar (brainstem, cerebellum). Watershed zones between territories are classic sites of hypoperfusion injury.
- Cranial nerve nuclei and brainstem levels: midbrain (CN III/IV), pons (CN V–VIII), medulla (CN IX–XII). Know the medial vs lateral syndromes.
- Spinal cord: dorsal columns (proprioception/vibration), lateral corticospinal, spinothalamic (crosses within 1–2 segments), anterior horn. The rule of the cord is that lesions produce dissociated sensory loss.
- Peripheral nerve and muscle: nerve fascicular architecture, myelin vs axonal; muscle fiber types (type I slow, type II fast).
Traps:
- Confusing the internal capsule (compact, lacunar strokes) with cortical lesions (patchy deficits).
- Forgetting that the hippocampus is medial temporal and supplied by PCA branches - relevant in hypoxia and Alzheimer disease staging.
- Mixing up dorsal root ganglion (pseudounipolar, no synapses) with autonomic ganglia (multipolar, synapses).
Rule of thumb: When a question describes a deficit, first draw the level (cortex, capsule, brainstem, cord, root, nerve, muscle), then ask which tissue is involved. Anatomy narrows the differential before histology does.