Classic Histology Signs

If neuroradiology has its hummingbirds and pandas, neuropathology has an even older bestiary of buzzwords — fried eggs, onion bulbs, owls, ragged-red fibers, and rosettes named after the anatomists who first drew them. These are the slide-side shorthand that lets a pathologist glance down the microscope and say “schwannoma” or “glioblastoma” before the immunostains are even cut. They are genuinely high-yield: a single pattern can pin down a tumor lineage, a viral culprit, or a mitochondrial myopathy. Below is an accuracy-first tour of the classics, grouped by category and paired with the entity each one points to. (The degenerative protein inclusions — Lewy bodies, neurofibrillary tangles, and friends — get their own companion page, so they are deliberately left out here.)

CNS tumor patterns

• Rosenthal fibers + eosinophilic granular bodies — corkscrew-shaped, brightly eosinophilic cytoplasmic condensations of glial filaments alongside globular granular bodies are the duo of pilocytic astrocytoma. Rosenthal fibers are not unique to tumor, however — they are also the histologic hallmark of Alexander disease and pile up at the edges of any chronically gliotic, slow-growing lesion.
• Pseudopalisading necrosis + microvascular (endothelial) proliferation — tumor cells lined up like a picket fence around serpiginous zones of necrosis, plus tufted, glomeruloid proliferation of small vessels, are the classic histologic hallmarks of glioblastoma. Under the WHO Classification of Tumours of the CNS, 5th edition (2021), glioblastoma is defined as an adult-type diffuse glioma that is IDH-wildtype, CNS WHO grade 4. In an adult IDH-wildtype diffuse astrocytic glioma, a diagnosis of “glioblastoma, IDH-wildtype” can be established by:
  • Necrosis (including pseudopalisading necrosis), or
  • Microvascular proliferation, or
  • Molecular features even in their absence — TERT promoter mutation, EGFR amplification, or combined gain of chromosome 7 and loss of chromosome 10 (+7/−10).
  Crucially, an IDH-mutant astrocytic tumor showing grade-4 features (necrosis or microvascular proliferation) is no longer called glioblastoma; it is classified as “astrocytoma, IDH-mutant, CNS WHO grade 4.”
• “Fried-egg” cells + “chicken-wire” capillaries — uniform round nuclei with clear perinuclear halos (a formalin-fixation artifact, classically) set against a delicate branching capillary network are the look of oligodendroglioma, the entity defined molecularly by IDH mutation and 1p/19q co-deletion.
• Perivascular pseudorosettes — tumor cells radiating processes toward a central vessel, leaving a fibrillary perivascular clear zone, point to ependymoma. Distinguish these from true ependymal rosettes (cells around an empty central lumen), which are more specific but less common.
• Homer Wright rosettes — cells encircling a central tangle of neuropil (no lumen) — are seen in medulloblastoma and in neuroblastoma. Contrast with Flexner–Wintersteiner rosettes, which surround a true central lumen and are characteristic of retinoblastoma.
• Psammoma bodies + whorls — concentric laminated calcifications nested within onion-skin spirals of meningothelial cells are the signature of meningioma.
• Antoni A and Antoni B areas + Verocay bodies — compact spindle-cell zones (Antoni A) alternating with loose, myxoid, hypocellular zones (Antoni B), with palisading nuclei stacked into anuclear bands (Verocay bodies), define schwannoma.
• Secondary structures of Scherer — perineuronal and perivascular satellitosis, subpial accumulation, and tracking along white-matter fibers — mark how an infiltrating (diffuse) glioma colonizes pre-existing brain architecture rather than forming a discrete mass.

Infectious and inflammatory patterns

• Microglial nodules + neuronophagia — clusters of activated microglia, often swarming a dying neuron — are the stereotyped tissue reaction of viral encephalitis. In HIV encephalitis they are accompanied by multinucleated giant cells formed by virus-driven fusion of infected macrophages/microglia.
• Negri bodies — eosinophilic cytoplasmic inclusions, found especially in hippocampal pyramidal and cerebellar Purkinje neurons — are pathognomonic for rabies.
• Cowdry type A intranuclear inclusions — eosinophilic inclusions with a surrounding clear halo and marginated chromatin — are seen in herpes simplex encephalitis and other herpesvirus infections.

Muscle and nerve patterns

• Ragged-red fibers — fibers with subsarcolemmal accumulations of abnormal mitochondria that stain red on the modified Gomori trichrome — are the morphologic marker of mitochondrial myopathy.
• Onion-bulb formations — concentric whorls of Schwann-cell processes around an axon, seen on nerve biopsy — reflect repeated demyelination and remyelination, classically in CMT type 1 (hereditary) and CIDP (acquired).
• Rimmed vacuoles — vacuoles lined by basophilic granular material on frozen sections — are characteristic of inclusion body myositis (and appear in some inherited myopathies).

Quick-reference table

A word of caution

These patterns are orienting clues, not final diagnoses. Modern neuropathology confirms a histologic impression with immunohistochemistry and molecular testing — GFAP, IDH1 R132H, ATRX, 1p/19q status, and the rest — and the 2021 WHO classification of CNS tumors makes molecular features diagnostic, sometimes overriding what the H&E suggests. Read every buzzword back against the immunostains, the molecular panel, and the clinical and radiologic context before letting a pattern drive the diagnosis.