CNS Pathology
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Direct answer
Central nervous system pathology covers malformations such as neural tube defects preventable by periconceptional folic acid, cerebrovascular disease — middle cerebral ischaemia, hypertensive putaminal haemorrhage and berry-aneurysm subarachnoid haemorrhage — infections with their cerebrospinal fluid patterns, multiple sclerosis, the degenerative diseases from Alzheimer to Parkinson, and tumours by age and location, with glioblastoma the commonest primary adult malignancy and medulloblastoma the childhood posterior fossa tumour. Indian angles include tuberculous meningitis and neurocysticercosis as seizure causes.
What you must remember
- Malformations: anencephaly from rostral neuropore failure, spina bifida from caudal failure, prevented by periconceptional folate; Chiari II pairs with lumbar myelomeningocele; Dandy-Walker shows vermis hypoplasia with cystic fourth ventricle; normal pressure hydrocephalus gives gait apraxia, dementia and incontinence.
- Stroke: ischaemic infarction in middle cerebral territory shows red neurons within a day, neutrophils at two to three days, then macrophages and gliosis; lacunar infarcts from hypertensive arteriolosclerosis hit deep grey matter; hypertensive haemorrhage favours putamen, thalamus, pons and cerebellum from Charcot-Bouchard microaneurysms; lobar haemorrhage in elders suggests amyloid angiopathy; subarachnoid haemorrhage — thunderclap headache, xanthochromia, nimodipine against vasospasm.
- Infections: bacterial meningitis — neutrophils, high protein, very low glucose, pneumococcus commonest in adults; viral — lymphocytes with normal glucose, herpes simplex in temporal lobes; tuberculous — lymphocytes, high protein, low glucose, cobweb clot and cranial nerve palsies, common in India; cryptococcal with India ink-positive yeasts in HIV; ring-enhancing brain abscess; neurocysticercosis with seizures and an eccentric scolex, treated with albendazole and steroids; rabies Negri bodies; prion spongiform change.
- Demyelination: multiple sclerosis with periventricular plaques, oligoclonal CSF bands, optic neuritis and internuclear ophthalmoplegia; neuromyelitis optica with aquaporin-4 antibodies.
- Degenerative: Alzheimer — commonest dementia — with amyloid plaques and tau tangles; Lewy body dementia with alpha-synuclein, fluctuating cognition and hallucinations; Parkinson with depigmented substantia nigra and Lewy bodies; amyotrophic lateral sclerosis with upper and lower motor neuron loss; Huntington with CAG expansion and caudate atrophy.
- Tumours by age: adults — glioblastoma with pseudopalisading necrosis and GFAP; meningioma from arachnoid cap cells with psammoma bodies and a dural tail; vestibular schwannoma at the cerebellopontine angle, bilateral in NF2; metastases commonest overall. Children — medulloblastoma of the vermis with Homer-Wright rosettes and CSF drop metastases; pilocytic astrocytoma with Rosenthal fibres.
- Raised pressure: papilloedema; uncal herniation compressing the third nerve with a blown pupil.
Common confusion
CSF patterns decide meningitis: neutrophils with very low glucose for bacteria, lymphocytes with normal glucose for viruses, lymphocytes with low glucose and cobweb for tuberculosis, India ink for cryptococcus. Putaminal haemorrhage comes from Charcot-Bouchard aneurysms; subarachnoid from berry aneurysms. Alzheimer plaques are extracellular amyloid while tangles are intracellular tau; glioblastoma pseudopalisading distinguishes it from sharply outlined metastases at grey-white junctions.
Exam-focused takeaway
FMGE quotes CSF values and expects the organism, gives thunderclap headache and expects aneurysm care with nimodipine, and asks tumours from age, site and histology phrases — pseudopalisading necrosis, Rosenthal fibres, Homer-Wright rosettes. Indian favourites include tuberculous CSF, neurocysticercosis seizures and childhood posterior fossa tumours.
Frequently asked questions
Which artery is most often involved in ischaemic stroke?
The middle cerebral artery, giving contralateral face-and-arm weakness with aphasia when dominant; lacunar disease strikes deep small vessels in hypertension and diabetes.
What is the CSF pattern of tuberculous meningitis?
Lymphocytic pleocytosis with high protein, low glucose and a cobweb coagulum, often with basal enhancement and cranial nerve palsies; treated with antitubercular therapy and corticosteroids.
What causes subarachnoid haemorrhage in a young adult?
Rupture of a circle of Willis berry aneurysm, linked to hypertension, smoking and polycystic kidney disease; CT confirms and nimodipine limits vasospasm.
Which is the commonest primary malignant brain tumour of adults?
Glioblastoma, with pseudopalisading necrosis and microvascular proliferation crossing the corpus callosum; prognosis remains poor despite multimodal therapy.