Central nervous system (Condensed) 2026

Reduction of brain parenchyma volume (e.g., Alzheimer) caused by cerebral atrophy, causing relatively increased size of the ventricles filled with CSF

Hydrocephalus ex vacuo

Neurologic condition characterized by elevated ICP due to estrogen/retinoid acid effects on the epithelial cells, causing resistance to CSF outflow

Pseudotumor cerebri (idiopathic intracranial hypertension) - Mimics the presence of a brain tumor, hence the name.

Unilateral/asymmetric expansion of the cerebral hemisphere such that the cingulate gyrus herniates under the falx cerebri

Subfalcine herniation

Major artery compressed in subfalcine herniation, causing lower limb neurologic defects

Anterior cerebral artery (ACA)

Displacement of the medial aspect of the temporal lobe across the tentorium cerebelli due to elevated ICP

Transtentorial (uncal) herniation

Cranial nerve and major cerebral artery damaged in uncal herniation, leading to ipsilateral mydriasis and visual disturbances (2)

CN III, Posterior cerebral artery - Can also lead to hemiparesis

Linear/flame-shaped hemorrhage of the midbrain and pons caused by progressive uncal herniation

Duret hemorrhages

Clinical features of tonsillar herniation, wherein the cerebellar tonsils herniate through the foramen magnum

Cardiac and respiratory depression (due to brainstem compression)

Congenital neural tube defect, in which part of the vertebra fails to close, but the spinal cord, meninges, and overlying skin remain intact

Spina bifida oculta

Extension of the spinal cord and meninges through a vertebral column defect

Myelomeningocele (meningocele only if just the meninges)

Extrusion of malformed brain tissue through a midline cranial defect; mostly the occipital area

Encephalocele

A defect caused by failure of the anterior neural tube to close, causing the absence of most of the brain and calvarium

Cranial dysraphism - anencephaly

Caudal displacement of the cerebellar tonsils, vermis, and fourth ventricle through the foramen magnum, causing obstructive hydrocephalus and associated with lumbar myelomeningocele

Chiari II malformation (Arnold Chiari)

Low-lying cerebellar tonsils through the foramen magnum; less severe compared to Chiari II malformation

Chiari I malformation

Congenital malformation caused by hypoplasia/agenesis of the cerebellar vermis, leading to cystic enlargement of the 4th ventricle and an enlarged posterior fossa

Dandy Walker malformation

Abnormal fluid-filled cavity in the inner portion of the central canal of the spinal cord

Syringomyelia

Distribution of decreased sensitivity to pain and temperature

Cape-like distribution in the upper extremities

Degeneration of the dorsal columns of the spinal cord caused by tertiary syphilis, causing dysesthesias, gait ataxia, and progressive loss of proprioception

Tabes dorsalis

Lobe of the brain usually affected in HSV hemorrhagic necrotizing encephalitis

Medial temporal lobe

Part of the brain where rabies causes the most severe neuronal degeneration

Brainstem

Cytoplasmic, round to oval, eosinophilic inclusions in the pyramidal neurons of the hippocampus and Purkinje cells of the cerebellum in rabies

Negri bodies

Lacerated artery that leads to epidural hematoma after traumatic head injury

Middle meningeal artery

Most common site of lacunar infarcts in the brain

Putamen

Most common site of deep parenchymal hemorrhage of the brain

Putamen

Most common type of intracranial aneurysm and the most common cause of spontaneous subarachnoid hemorrhages, usually associated with ADPKD, Ehlers Danlos syndrome, and Marfan syndrome

Saccular "berry" aneurysms - Most commonly occurring at the ACA-AcoA junction (40%)

Chronic demyelinating disease of the CNS, characterized by a relapsing and remitting course, commonly manifesting initially with a unilateral optic neuritis

Multiple sclerosis - A type IV hypersensitivity reaction

Characteristic bands that represent IgG subfractions on electrophoresis of the CSF; seen in multiple sclerosis

Oligoclonal IgG bands

Most common prion disease; due to iatrogenic transmission of a misfolded prion that accumulates in neurons, causing rapidly progressive dementia, startle myoclonus, and ataxia

Creutzfeldt-Jakob disease - Uniformly fatal

Most common cause of dementia in older adults; neurodegenerative disorder characterized by progressive behavioral and cognitive dysfunction; due to deposition of β amyloid plaques and neurofibrillary tangles

Alzheimer disease - Associated with cortical atrophy, with narrowed gyri and widened sulci

Focal spherical collections of dilated, tortuous axonal or dendritic process around a central Aβ amyloid core; specific for Alzheimer dse.

Neuritic plaques

Collection of intracellular aggregates composed of hyperphosphorylated tau; accumulation of which correlates well with degree of dementia in Alzheimer ds.

Neurofibrillary tangles - Not specific for AD

Neurodegenerative disorder characterized by progressive neuronal loss in the frontal and/or temporal cortices, causing early onset personality and behavioral changes, followed by aphasia and dementia

Frontotemporal dementia (Pick disease)

Neurodegenerative disorder involving progressive depletion of dopaminergic neurons in the basal ganglia, particularly the substantia nigra; (+) Lewy bodies

Parkinson disease

Triad of Parkinsonism

Slowed voluntary movement, Rigidity, Pill-rolling tremor

Autosomal dominant neurodegenerative movement disorder characterized by chorea, severe dementia, and athetosis; progressive and fatal

Huntington disease

Huntington disease is caused by a ____ expansion on the Huntingtin (HTT) gene, causing loss of cortical and striatal neurons that dampen motor output.

CAG, This is a trinucleotide repeat that increases in number in Huntington disease.

Primarily affected structures of the brain that are affected in Huntington disease (3)

Cortex (frontal > parietal), caudate, and putamen

Trinucleotide repeat expansion seen in Friedreich ataxia

GAA - In the frataxin gene (Ch9)

Non-neurological manifestations of Friedreich ataxia on the heart and endocrine system (2)

Hypertrophic cardiomyopathy, Diabetes mellitus. The GAA expansion in the frataxin gene causes neuronal, cardiomyocyte, and pancreatic beta cell death.

Triad of Wernicke encephalopathy

Ataxia, Confusion, Ophthalmoplegia (ACO)

Triad of Korsakoff syndrome

Confabulation, Hallucinations, Amenia (CHA)

Spinal tracts that are affected and demyelinated in subacute combined degeneration (3)

Spinocerebellar tract, Lateral corticospinal tract, Dorsal columns

Most common group of primary brain tumors

Gliomas

Most common type of glioma

Astrocytoma

Primary CNS tumor that arises from oligodendrocytes, most commonly occurring at the cerebral hemispheres; associated with chicken-wire vasculature & calcifications; (+) fried egg appearance

Oligodendroglioma

Most common primary malignant brain tumor in adults; typically developing in the white matter of the cerebral hemispheres

Glioblastoma

Most common glioma in children; appearing at the cerebellum as a well-circumscribed cystic lesion with biphasic architecture; (+) hairlike processes and Rosenthal fibers

Pilocytic astrocytoma

Brain tumor that arises in cells that line the walls of the cerebral ventricles and central canal of the spine; (+) perivascular pseudorosettes

Ependymoma

Neurocutaneous syndrome that is associated with the development of ependymomas

Neurofibromatosis type II

2nd most common malignant tumor in children; usually arising in the cerebellum; (+) Homer-Wright pseudorosettes; (+) drop metastasis in the cauda equina

Medulloblastoma

Slow-growing extra-axial tumor that arises from the arachnoid cap cells of the arachnoid villi, with a dural tail; benign; (+) Psammoma bodies

Meningioma - Associated with NF2 loss

Most common subtype of lymphoma in primary CNS lymphoma

Diffuse large B cell lymphoma (DLBCL)

Most common CNS neoplasm in adults

Metastasis