1. d. Hemangioblastoma is a hypercellular, vascular tumor containing foamy interstitial cells, which represent the actual neoplastic element. Hemangioblastomas occur most commonly in the cerebellum and are often associated with von Hippel-Lindau syndrome. Subependymal giant cell astrocytoma is an intraventricular tumor (lateral ventricles) resembling gemistocytic astrocytoma that is usually seen in the context of tuberous sclerosis. Pilocytic astrocytomas are biphasic neoplasms composed of alternating areas of compact spindle cells and more loosely textured zones and often accompanied by Rosenthal fibers.

2. b. Acute hypoxic/ischemic injury is associated (if the patient survives at least six hours) with shrunken eosinophilic neurons. Certain populations of neurons are selectively vulnerable, especially large neurons in CA1 sector of the hippocampus, the Purkinje cells of the cerebellum, and neurons of layers 3 through 5 of the cerebral cortex. Neurofibrillary tangles, granulovacuolar degeneration, and Hirano bodies are neurodegenerative changes. CA2 is the so-called “resistant zone” of the hippocampus that is less vulnerable to hypoxia/ ischemia.

3. d. Berry aneurysms involving the circle of Willis are uncommon in children. The photomicrograph shows the basilar aspect of the brain with a berry aneurysm at the trifurcation. The risk of rupture, which produces hemorrhage into the subarachnoid space at the base of the brain, is greatest for females in the fifth decade.

4. e. Lewy bodies are inclusion bodies found in Parkinson disease and diffuse Lewy body disease. In pure Parkinson disease, Lewy bodies are located predominantly in the pigmented neurons in the substantia nigra (as depicted in the photomicrograph) and locus ceruleus, whereas in diffuse Lewy body disease, they are also found in the cerebral cortex.

5. b. Medulloblastoma and ependymoma are the second and third most common primary central nervous system (CNS) neoplasms in children. Histopathologically, medulloblastomas are densely cellular “small blue cell” tumors that typically contain frequent mitoses and apoptotic nuclei, and sometimes frank necrosis. Ependymomas are glial neoplasms that are usually recognized by the presence of perivascular pseudorosettes. Overall, low-grade astrocytomas are the most common. In very young children, medulloblastoma is more common than astrocytic neoplasms. Glioblastoma multiforme and metastatic disease are extremely uncommon in children and are much more likely to occur in the over-60 population.

6. c. The gross photo shows a midsagittal section of brain with a large mass in the region of the posterior third ventricle. The most common entity in this location in children is a pineal germinoma. Parinaud syndrome is associated with dorsal midbrain (pineal region) lesions and is characterized by vertical gaze palsy, convergenceretraction nystagmus, and light-near dissociation. Seizures are typically related to cortical lesions, and hemiballismus occurs with lesions of the subthalamic nucleus. Cortical blindness is seen with bilateral impairment of the posterior occipital lobes, especially those lesions that involve the calcarine fissures bilaterally.

7. e. Damage to axons, also termed diffuse axonal injury (DAI) or traumatic axonal injury (TAI), is an almost universal finding in cases of mild, moderate, and severe head trauma. Although not specific for trauma, β-amyloid precursor protein (β-APP) is a useful stain for highlighting axonal spheroids.

8. e. Huntington disease is a rare autosomal dominant inherited disease with a mutation in the IT15 gene, located on chromosome 4, which alters the huntingtin protein. There are increased CAG tandem repeat sequences in the gene. The gross photo shows a coronal section of brain with bilateral effacement of the caudate nucleus. Choreiform movement and not echolalia characterize the disease. Echolalia is more common in autism.

9. a. In cases of idiopathic Parkinson disease, the brain shows pallor of the substantia nigra and locus ceruleus accompanied by neuronal loss, extracellular pigment, and gliosis. The remaining neurons may contain Lewy bodies, which are eosinophilic cytoplasmic structures. Ultrastructurally, Lewy bodies are composed of filaments that form the densely packed core. These filaments are made of alpha-synuclein, a lipid-binding protein that can be demonstrated by immunohistochemical methods (image b).

10. c. Cerebral amyloid angiopathy is the most common cause of lobar hemorrhage in the elderly. The amyloidogenic proteins, nearly the same as those found in Alzheimer disease, are deposited in meningeal and cerebral vessels, thus weakening their walls and predisposing to hemorrhage.

11. e. Carbon monoxide poisoning typically affects both globus pallidi and chronic lesions are cavitary.

12. a. Cerebral malaria is not caused by P. ovale, but by Plasmodium falciparum, which infects red blood cells, causing them to clump together (rosetting) and stick to endothelial cells (sequestration). Accordingly, cerebral blood vessels are plugged with parasitized red blood cells containing dots of hemozoin pigment, which leads to stasis and tissue hypoxia. This sets the stage for ring hemorrhages and small collections of inflammatory cells known as Dürck granulomas.

13. e. All of these statements apply to the diagnosis of multiple sclerosis. The photomicrograph shows a sharply demarcated focus of demyelination (myelin pallor) adjacent to the anterior horn of the lateral ventricle in a section stained for myelin.

14. c. Creutzfeldt-Jacob disease is a form of spongiform encephalopathy thought to be caused by prions that manifest clinically by rapidly progressive dementia. The spongiform change is particularly prominent in the cerebral cortex or gray matter of the brain. Accumulation of the abnormal beta-pleated sheet isoform, termed PrPsc for PrP (protease resistant) and (scrapie) is considered responsible for the pathogenesis of this disease.

15. b. Glioblastoma multiforme is an extremely heterogeneous tumor characterized by varying degrees of increased cellularity, pleomorphism, mitoses, endothelial proliferation, and necrosis. Pseudopalisading necrosis shown in the photomicrograph is a common feature. Amplification of epidermal growth factor receptor (EGFR) typically indicates a primary (de novo) glioblastoma multiforme, whereas its absence suggests a secondary glioblastoma.

16. a. The gross photo shows a dural-based meningioma and not glioblastoma multiforme, the most common primary brain tumor in adults.

18. d. Cataracts represent lenticular opacities. Primary closed angle glaucoma develops in eyes with shallow anterior chambers.

19. c. Vein of Galen aneurysm is a rare congenital malformation of blood vessels that results in high-output congestive heart failure or may present with developmental delay, hydrocephalus, and seizures. The vein of Galen drains the anterior and central regions of the brain into the sinuses of the posterior cerebral fossa.

20. b. Transtentorial or mesial temporal herniation occurs when the medial aspect of the temporal lobe is compressed against the tentorium cerebelli. When this occurs, displacement of the temporal lobe compromises the third cranial nerve, resulting in pupillary dilatation and impaired ocular movements.