ABPath Neuropathology key terms

An elongated, eosinophilic, corkscrew-shaped or granular structure seen in astrocytes, typically in pilocytic astrocytoma and long-standing gliosis; it represents abnormal protein accumulation within astrocytic processes.

A pattern in which tumor cells line up around zones of dead tissue, classically seen in glioblastoma; the arrangement reflects rapid growth outstripping blood supply rather than a true capsule.

Multiplication of small blood vessels with plump endothelial and smooth muscle cells forming glomeruloid tufts within a tumor; a hallmark of glioblastoma and an indicator of high-grade behavior.

An astrocyte with abundant eosinophilic cytoplasm and an eccentric nucleus, formed by reactive or neoplastic cells; common in reactive gliosis and in gemistocytic astrocytoma.

Proliferation and hypertrophy of astrocytes in response to injury of the central nervous system, producing a dense meshwork of processes; it is a nonspecific scar-forming reaction rather than a neoplasm.

A low-grade astrocytic tumor, most often in children and in the cerebellum, composed of biphasic compact and loose areas with Rosenthal fibers and eosinophilic granular bodies; often associated with BRAF alterations.

The most common malignant primary brain tumor in adults, defined by astrocytic differentiation with necrosis and/or microvascular proliferation; it is diffusely infiltrative and carries a poor prognosis.

A ring of tumor cells arranged around a central lumen, mimicking the ventricular lining; typical of ependymoma and distinct from the perivascular pseudorosette.

A radial arrangement of tumor cells around a blood vessel, with a nucleus-free fibrillary zone between cells and vessel wall; characteristic of ependymoma and some other gliomas.

A glial tumor arising from ependymal cells, often in the ventricular system or spinal cord, showing uniform cells, perivascular pseudorosettes, and sometimes true ependymal rosettes.

An embryonal malignant tumor of the cerebellum, most common in children, composed of small round blue cells with high mitotic activity and a tendency to spread through cerebrospinal fluid.

Fibrous connective tissue proliferation induced by tumor, often seen around metastatic carcinoma or in desmoplastic medulloblastoma; it appears as collagen bands separating nests of tumor cells.

Dissemination of tumor cells through the cerebrospinal fluid into the pia-arachnoid space, producing meningeal enhancement and possible hydrocephalus; typical of medulloblastoma and other embryonal tumors.

A round, brightly eosinophilic protein droplet found in astrocytes, especially in pilocytic astrocytoma and pleomorphic xanthoastrocytoma; it is a degenerative product, not a specific tumor marker.

A round, eosinophilic neuronal inclusion with a pale halo, composed largely of alpha-synuclein; found in substantia nigra neurons in Parkinson disease and in cortical neurons in dementia with Lewy bodies.

A flame-shaped intracellular aggregate of hyperphosphorylated tau protein in neurons, characteristic of Alzheimer disease and other tauopathies; its distribution correlates with cognitive decline.

An extracellular deposit of amyloid-beta peptide in brain parenchyma, either diffuse or with a dense core surrounded by dystrophic neurites; a defining lesion of Alzheimer disease.

Deposition of amyloid-beta in the walls of leptomeningeal and cortical small vessels, causing vessel fragility and lobar hemorrhage in older adults; often coexists with Alzheimer disease.

A neuronal protein that aggregates into Lewy bodies and glial cytoplasmic inclusions; its abnormal deposition defines Parkinson disease, dementia with Lewy bodies, and multiple system atrophy.

A normal cell-surface glycoprotein that, in a misfolded infectious form, accumulates in the brain and causes spongiform change; it underlies Creutzfeldt-Jakob disease and related disorders.

Vacuolation of the neuropil producing a sponge-like appearance, typically without inflammation; the hallmark of prion disease but also seen in edema and some metabolic conditions.

Loss of myelin with relative preservation of axons, producing pale areas on myelin stains; it occurs in immune-mediated diseases such as multiple sclerosis and in toxic or metabolic injury.

A histochemical stain that binds myelin lipids and colors normal white matter blue; used to demonstrate myelin loss and to outline demyelinating lesions in tissue sections.

A swollen, rounded axonal segment filled with accumulated organelles and proteins, formed when axonal transport is interrupted by injury or disease; visible on silver or immunohistochemical stains.

Traumatic shearing of axons in white matter tracts, especially at gray-white junctions and the brainstem, producing axonal spheroids and sometimes small hemorrhages; a major cause of coma after trauma.

Displacement of brain tissue across dural compartments or through the foramen magnum due to mass effect; it compresses vessels and cranial nerves and can cause secondary hemorrhage or infarction.

Linear or flame-shaped hemorrhage in the midbrain and pons caused by downward transtentorial herniation, resulting from stretching and tearing of penetrating brainstem vessels.

Abnormal accumulation of fluid in brain tissue, either intracellular (cytotoxic) or extracellular (vasogenic), causing swelling, flattened gyri, and narrowed sulci; it raises intracranial pressure.

Degeneration of the axon and its myelin distal to a nerve injury, followed by macrophage clearance and later remyelination by Schwann cells; it proceeds over days to weeks.

A disorganized tangle of regenerating nerve fibers and Schwann cells at the end of a severed peripheral nerve, forming a painful nodule; traumatic neuromas are distinct from true neoplasms.

A benign peripheral nerve sheath tumor composed of Schwann cells, showing Antoni A and B areas and Verocay bodies; commonly arises from vestibular nerve as an acoustic neuroma.

A palisade of elongated tumor cell nuclei arranged in parallel rows separated by fibrillary processes, seen in the Antoni A areas of schwannoma.

A benign nerve sheath tumor containing a mixture of Schwann cells, fibroblasts, and perineurial cells embedded in collagen, often arising within a nerve; associated with neurofibromatosis type 1.

A usually benign tumor arising from arachnoid cap cells, forming whorls and psammoma bodies and often attached to dura; it can compress adjacent brain without invading it.

A concentrically laminated, calcified basophilic structure found in meningioma, papillary thyroid carcinoma, and some other tumors; it represents dystrophic calcification of degenerated cells.

Rapid intraoperative tissue preparation by freezing and cutting, used to give a preliminary diagnosis that guides surgical decisions; it is less precise than permanent paraffin sections.

Image-guided sampling of a deep brain lesion through a small burr hole, used when resection is unsafe; small sample size and sampling error limit interpretation.

Irreversible cessation of all brain and brainstem function, established by clinical criteria including absent brainstem reflexes and apnea testing; neuropathology may be requested to confirm findings.