Gliosis vs Glioma: 5 Ways to Tell Them Apart (Morphology, IDH1, ATRX, p53) with MCQs

Reactive astrocytes for gliosis vs glioma

Subtitle: Five ways to tell reactive gliosis from glioma: cellularity and spacing, nuclear features, margins, proliferation and IHC (IDH1 R132H, ATRX, p53), plus mimics such as tumefactive demyelination, with 10 MCQs.

Author: PathologyMCQ Editorial Board

Category: Neuropathology

Last Updated: October 2026

Read Time: 6 minutes

At-a-Glance

Gliosis is a reactive process (infarct, demyelination, infection, around tumours); gliomas are neoplastic and often have gliosis at their edges.
Spacing: gliosis is evenly spaced; glioma is irregular and crowded.
Nuclei: gliosis nuclei are bland and do not touch; glioma nuclei are atypical, angulated and overlap.
IHC: IDH1 R132H positivity, ATRX loss or strong p53 indicates glioma; never seen in gliosis.
Ki-67 is low in gliosis, but also low in many low-grade gliomas.

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Comparison Table

Gliosis vs glioma

Feature	Reactive gliosis	Diffuse glioma
Cellularity	Mildly increased, even	Increased, uneven
Spacing	Evenly spaced astrocytes	Irregular clusters and crowding
Nuclei	Bland, round to oval, do not touch	Atypical, hyperchromatic, angulated, overlap
Processes	Long, symmetrical, radiating (stellate)	Short, irregular; naked nuclei
Secondary structures	Absent	Perineuronal satellitosis, subpial and perivascular clustering
Mitoses / Ki-67	Rare; Ki-67 low	Variable; may be low in grade 2
IDH1 R132H, ATRX, p53	Negative / retained / weak	IDH1 R132H+, ATRX loss, p53 strong (astrocytoma)
Margins over time	Contracts	Expands

5 ways to differentiate gliosis and glioma.

1–3. Cellularity, Nuclei and Margins

Cellular density: even in gliosis, uneven in glioma.
Nuclei: in gliosis they do not touch each other; in glioma they often overlap and are irregular.
Margins: gliomas expand and infiltrate; gliosis contracts with time. Serial imaging helps.

4. Proliferation

Mitoses are rare in gliosis and the Ki-67 index is usually low. However, IDH-mutant grade 2 gliomas can also have a low Ki-67, so proliferation alone cannot exclude glioma.

5. Immunohistochemistry

IDH1 R132H: positive tumour cells confirm an IDH-mutant glioma.
ATRX: nuclear loss supports IDH-mutant astrocytoma (retained in gliosis).
p53: strong diffuse staining in many astrocytomas; reactive cells show weak, patchy staining.
H3 K27M (midline) and BRAF V600E can also confirm a neoplasm.
GFAP is positive in both and does not help.

Mimics and Pitfalls

Tumefactive demyelination: sheets of CD68+ macrophages, Creutzfeldt cells, myelin loss with axonal preservation.
Piloid gliosis: Rosenthal fibres around craniopharyngioma, haemangioblastoma or syrinx can mimic pilocytic astrocytoma.
Infarct and abscess margins: gemistocytes and reactive changes.
Gliomatosis cerebri is no longer a separate entity: it is a growth pattern of diffuse glioma involving three or more lobes.

Video

Related: WHO CNS5 updates for gliomas →

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Gliosis vs glioma: 10 MCQs

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Exam Pearls

Even spacing and bland nuclei = gliosis; crowding, atypia and secondary structures = glioma.
IDH1 R132H positive or ATRX lost = glioma.
Creutzfeldt cells point to demyelination.
Gliomatosis cerebri is a growth pattern, not an entity.

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