Who cns tumors classification with histopathological images for pathologist

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I now have comprehensive content and images for a thorough answer. Let me compile the full CNS tumor classification guide for pathologists.

WHO Classification of CNS Tumors: A Histopathologist's Guide

The 2021 WHO Classification of Tumors of the Central Nervous System (5th edition) represents the most significant update in neuro-oncologic pathology, integrating molecular/genetic markers as essential diagnostic criteria alongside traditional histomorphology. Accurate diagnosis now requires both the glass slide and the molecular result.

Framework of the WHO 2021 CNS Classification

The key conceptual shift from prior editions:

Tumor type is defined by morphology + molecular markers together
CNS WHO grading is intratype (grade 2 astrocytoma vs. grade 3 astrocytoma are within the same entity, not a spectrum that includes glioblastoma)
Arabic numerals are used for grades (grade 2, 3, 4 - not II, III, IV)
Molecular features can override morphology for grading (e.g., IDH-wildtype diffuse astrocytoma with TERT mutation = glioblastoma grade 4, even without necrosis)

1. Diffuse Gliomas (Intraparenchymal, Infiltrating)

The most common group of primary brain tumors. They share diffuse infiltration of normal brain and are subclassified by three key features:

Feature	Astrocytoma, IDH-mutant	Oligodendroglioma	Glioblastoma, IDH-wt
IDH status	Mutant	Mutant	Wildtype
Other genetics	TP53 mut, ATRX mut, CDKN2A-HD (grade 4)	1p/19q codeletion	+7/-10, TERT-promoter mut, EGFR amp
Grades	2, 3, 4	2 or 3	4 (by definition)
Morphology	Nuclear atypia; mitoses (grade 3); MVP/necrosis (grade 4)	Round nuclei, clear halos; mitoses + MVP/necrosis (grade 3)	Nuclear atypia, mitoses, MVP, necrosis

(Robbins, Cotran & Kumar Pathologic Basis of Disease, Table 28.5)

1a. Astrocytoma, IDH-mutant (WHO Grades 2-4)

Key histologic features:

Poorly demarcated, infiltrative gray tumor expanding white matter
Hypercellularity with enlarged, elongated or irregular hyperchromatic nuclei embedded in a fibrillary background
GFAP-positive fibrillary matrix; tumor cells show IDH1 R132H immunopositivity (inset)
Grade 3: increased cellularity + readily detectable mitoses
Grade 4: microvascular proliferation (multilayered small vessels) + necrosis and/or homozygous CDKN2A deletion

Gross & histology (IDH-mutant astrocytoma):

Astrocytoma IDH-mutant - coronal section (A) showing left frontal white matter expansion; (B) hyperchromatic nuclei in fibrillary matrix with IDH1 R132H immunostain inset

Fig. 28.46 - Astrocytoma, IDH-mutant. (A) Coronal section: left frontal white matter expanded with blurring of corticomedullary junction. (B) Enlarged irregular hyperchromatic nuclei in fibrillary matrix; inset shows IDH1 p.R132H immunostain positivity with perineuronal satellitosis. - Robbins, Cotran & Kumar Pathologic Basis of Disease

1b. Glioblastoma, IDH-wildtype (WHO Grade 4)

The most common primary CNS malignancy in adults (>55 years); 14% of all primary CNS tumors. All IDH-wildtype diffuse astrocytomas are WHO grade 4 by definition.

Gross: Heterogeneous - firm gray-white areas + yellow necrotic zones + red hemorrhagic/hypervascular areas. Classic "butterfly glioma" crosses corpus callosum.

Key histologic features:

Pseudopalisading necrosis: serpentine bands of necrosis with viable hypercellular tumor arranged in palisades along the necrotic edge
Microvascular proliferation: tufts of cells piling up within vessel lumens (glomeruloid bodies)
High cellularity, marked nuclear pleomorphism, brisk mitoses
Ring-enhancing on MRI

Gross & histology (Glioblastoma):

Glioblastoma - gross section with central necrosis and hemorrhage; microscopy showing palisading necrosis and microvascular proliferation inset

Fig. 21.31 - Glioblastoma. (A) Necrotic, hemorrhagic infiltrating mass. (B) Serpiginous palisading necrosis; inset: microvascular proliferation (glomeruloid bodies). - Robbins & Kumar Basic Pathology

Glioblastoma gross section (axial cut):

Glioblastoma gross axial section showing central necrosis and hyperemic rim

Fig. 72.3 - Right hemispheric glioblastoma with central necrosis and hyperemic rim (Bradley and Daroff's Neurology in Clinical Practice)

1c. Oligodendroglioma, IDH-mutant and 1p/19q-codeleted (WHO Grades 2-3)

5-15% of gliomas; best prognosis among diffuse gliomas. Frontal/temporal lobe predilection; gyriform calcifications on imaging are characteristic.

Defining molecular signature: IDH1/2 mutation + 1p/19q codeletion (both required for diagnosis)

Key histologic features:

Uniformly round nuclei with bland chromatin
"Fried-egg" appearance: clear perinuclear halo (formalin fixation artifact; absent in frozen sections)
"Chicken-wire" vasculature: rich branching delicate capillary network
Cortical involvement, microcalcifications, mucin-rich microcystic spaces, perineuronal satellitosis
Grade 3 (anaplastic): hypercellularity, numerous mitoses, microvascular proliferation

Histology (Oligodendroglioma):

Oligodendroglioma - uniform round nuclei with clear perinuclear halos ("fried-egg" appearance) and chicken-wire capillary network (H&E x200)

Fig. 72.2 - Oligodendroglioma. Uniform round nuclei with clear perinuclear halos ("fried-egg" appearance); branching "chicken-wire" capillaries. H&E x200. - Bradley and Daroff's Neurology in Clinical Practice

2. Pilocytic Astrocytoma (WHO Grade 1)

A circumscribed (non-diffuse) glioma; distinct entity from diffuse astrocytomas. Most common pediatric CNS tumor; cerebellar predominance.

KIAA1549::BRAF fusion in >70% - a defining molecular feature
Grossly: well-demarcated cystic mass with enhancing mural nodule

Key histologic features:

Biphasic architecture: alternating loose "microcystic" and compact densely fibrillar areas
Bipolar cells with long thin "hair-like" (pilocytic) processes, GFAP-positive
Rosenthal fibers: eosinophilic corkscrew-shaped inclusions (pathognomonic in context)
Eosinophilic granular bodies (mulberry-like inclusions)
Microvascular proliferation and necrosis do NOT imply worse prognosis (unlike diffuse gliomas)

Gross & histology (Pilocytic Astrocytoma):

Pilocytic astrocytoma - (A) cerebellar cyst with mural nodule; (B) biphasic architecture; (C) Rosenthal fibers

Fig. 28.50 - Pilocytic astrocytoma. (A) Cerebellar cyst with mural nodule. (B) Sharp circumscription with biphasic loose/compact growth. (C) Rosenthal fibers (brightly eosinophilic corkscrew-shaped inclusions). - Robbins, Cotran & Kumar Pathologic Basis of Disease

3. Ependymoma (WHO Grades 2-3; Subependymoma Grade 1)

Arise from ependymal lining of ventricles and central canal. Location-defined classification in WHO 2021:

Supratentorial: often ZFTA::RELA fusion (poor prognosis) or YAP1 fusion (better prognosis)
Posterior fossa type A (PFA): H3K27me3 loss by IHC (poor prognosis)
Posterior fossa type B (PFB): H3K27me3 retained (better prognosis)
Spinal: NF2 mutation; rare MYCN-amplified (poor prognosis)

Key histologic features:

Perivascular pseudorosettes: tumor cells arranged around blood vessels with anuclear fibrillary zones (most common)
True ependymal rosettes/canals: tumor cells around central lumen (pathognomonic but less common)
GFAP-positive fibrillary background
Solid, non-infiltrative masses (unlike diffuse gliomas)

4. Medulloblastoma (WHO Grades 3-4 equivalent)

Most common malignant pediatric CNS tumor; arises in cerebellar vermis. Highly radiosensitive. WHO 2021 classifies by both histologic type and molecular group.

Molecular groups (prognosis-defining):

Group	Prognosis	Key Features
WNT-activated	~100% 5-year survival	CTNNB1 mutation, monosomy 6
SHH-activated	Intermediate	PTCH1/SMO mutations; TP53 mut (worse)
Group 3	Poor (20-30% survival)	MYC amplification; metastatic
Group 4	Intermediate	Most common; isochromosome 17q

Histologic subtypes:

Classic: sheets of small round blue cells (SRBCT), Homer-Wright rosettes (incomplete rosettes around neuropil)
Desmoplastic/nodular: pale "islands" surrounded by dense desmoplastic stroma (nodules = reticulin-poor)
Large cell/anaplastic: large cells with prominent nucleoli + nuclear molding (worst prognosis)
MBEN (medulloblastoma with extensive nodularity): florid nodular pattern, excellent prognosis in infants

Gross & histology (Medulloblastoma):

Medulloblastoma - (A) cerebellar vermis mass; (B) classic small blue cell pattern with Homer-Wright rosettes; (C) desmoplastic nodular pattern; (D) large cell/anaplastic pattern

Fig. 28.52 - Medulloblastoma. (A) Gross: cerebellar vermis replacement. (B) Classic type: dense sheets of small blue cells with Homer-Wright rosettes (arrows). (C) Desmoplastic/nodular pattern. (D) Large cell/anaplastic type. - Robbins, Cotran & Kumar Pathologic Basis of Disease

5. Meningioma (WHO Grades 1-3)

Arise from meningothelial (arachnoid cap) cells; most common primary intracranial tumor overall. Female predominance (2:1 overall; 10:1 for spinal). Prior radiation is a risk factor. NF2 mutation is the most common genetic alteration.

Histologic subtypes (Grade 1 - most):

Meningothelial: clusters of epithelioid cells with indiscernible cell membranes
Fibroblastic: intersecting fascicles of spindled cells + abundant collagen
Transitional: mixed features with numerous whorls
Psammomatous: abundant psammoma bodies (concentric calcified rings)
Secretory, microcystic, lymphoplasmacyte-rich, angiomatous (others)

Grade 2 (atypical, ~25%): increased mitotic index (≥4/10 HPF), brain invasion, or chordoid/clear cell pattern

Grade 3 (anaplastic, 1-3%): markedly elevated mitoses; resembles carcinoma or sarcoma; retains meningothelial features

Gross & histology (Meningioma):

Meningioma - (A) parasagittal lobulated dural mass; (B) whorled pattern with psammoma bodies (concentric calcification rings)

Fig. 28.53 - Meningioma. (A) Parasagittal multilobular meningioma compressing underlying brain. (B) Whorled cell growth with numerous psammoma bodies. - Robbins, Cotran & Kumar Pathologic Basis of Disease

6. Primary CNS Lymphoma

2% of extranodal lymphomas; most common CNS neoplasm in immunosuppressed patients
Virtually always diffuse large B-cell lymphoma (DLBCL)
Multifocal, periventricular, deep subcortical
Malignant cells accumulate around blood vessels (angiocentric pattern), express CD20
In immunosuppressed: necrosis prominent; EBV positive (EBER ISH)
In immunocompetent: PDL1 gene amplification common; worse prognosis than nodal DLBCL

7. Metastatic Tumors

Account for 25-50% of intracranial tumors in hospitalized patients. Common primaries (in order): lung > breast > melanoma > kidney > GI tract (~80% combined). Typically well-circumscribed, ring-enhancing, gray-white masses at gray-white matter junction. Always consider metastasis in older patients with multiple lesions.

Key Molecular Tests for Pathologists (WHO 2021)

Marker	Significance
IDH1/2 mutation	Distinguishes astrocytoma/oligodendroglioma from GBM and reactive gliosis
1p/19q codeletion	Defines oligodendroglioma (combined with IDH mutation)
ATRX/TP53	Supports astrocytoma lineage (mutually exclusive with 1p/19q codeletion)
TERT promoter mutation	Marks GBM (IDH-wt), oligodendroglioma; prognostic
EGFR amplification / +7/-10	Molecular hallmarks of GBM
CDKN2A homozygous deletion	Upgrades IDH-mutant astrocytoma to grade 4
MGMT promoter methylation	Predicts temozolomide sensitivity in GBM
H3K27me3 loss (IHC)	Identifies PFA ependymoma
KIAA1549::BRAF fusion	Diagnostic for pilocytic astrocytoma
CTNNB1 / WNT pathway	WNT medulloblastoma (best prognosis)
DNA methylation profiling	Gold standard for difficult cases; supersedes histology in ambiguous tumors

A 2025 JAMA Oncology review by Horbinski et al. (PMID: 39724142) emphasizes that routine advanced molecular profiling is now the standard of care - the cost is less than 5% of total CNS tumor treatment costs and consistently improves accuracy of diagnosis and grading, eligibility for clinical trials, and prediction of treatment response.

Grading Summary Table

Tumor	WHO Grade	Key Histologic Hallmark
Pilocytic astrocytoma	1	Biphasic, Rosenthal fibers, well-circumscribed
Astrocytoma, IDH-mutant	2	Hypercellular, nuclear atypia, infiltrative
Astrocytoma, IDH-mutant	3	+ Mitoses
Astrocytoma, IDH-mutant	4	+ MVP/necrosis or CDKN2A HD
Glioblastoma, IDH-wt	4	Palisading necrosis, MVP, pleomorphism
Oligodendroglioma	2	Fried-egg cells, chicken-wire vessels
Oligodendroglioma	3	+ Mitoses, MVP/necrosis
Ependymoma	2-3	Perivascular pseudorosettes
Medulloblastoma	4 (aggressive)	Small blue cells, Homer-Wright rosettes
Meningioma	1	Whorls, psammoma bodies
Meningioma	2 (atypical)	≥4 mitoses/10 HPF or brain invasion
Meningioma	3 (anaplastic)	Carcinoma/sarcoma-like, high mitoses

Sources: Robbins, Cotran & Kumar Pathologic Basis of Disease, p.1192-1200; Robbins & Kumar Basic Pathology, p.877; Bradley and Daroff's Neurology in Clinical Practice; Horbinski et al., JAMA Oncol 2025 (PMID: 39724142)

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CNS Tumor Classification Residents
Presentation · PPTX

What's inside (15 slides, dark navy + teal + amber theme):

Slide	Content
1	Title slide
2	Why WHO 2021 changed — before vs. after
3	CNS tumor categories overview map
4	Diffuse gliomas comparison table (Astrocytoma / Oligodendroglioma / GBM)
5	Astrocytoma, IDH-mutant — histopathology image + grading criteria (Gr 2/3/4)
6	Glioblastoma — gross + palisading necrosis histology + molecular criteria
7	Oligodendroglioma — "fried-egg" histology image + molecular/clinical details
8	Pilocytic Astrocytoma — biphasic/Rosenthal fiber histology + WHO Gr 1 pearls
9	Ependymoma — location-defined subtypes + pseudorosettes
10	Medulloblastoma — molecular groups (WNT/SHH/Gr3/Gr4) + histologic subtypes
11	Meningioma — psammoma body histology + Grade 1/2/3 criteria
12	CNS Lymphoma & Metastases — IHC panels, clinical traps
13	Essential molecular tests table (IDH, 1p/19q, TERT, MGMT, H3K27, BRAF, etc.)
14	Full grading summary table (all entities at a glance)
15	6 key take-aways for residents

Each content slide has a bottom footer callout flagging the most important exam/clinical pearl for that topic. All histopathology images are sourced from Robbins & Cotran and Bradley & Daroff, credited in-slide.

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