Page 638 - Concise Pathology for Exam Preparation ( PDFDrive )

23 The Central Nervous System 623

Microscopy:
• Cellular tumour composed of round to oval carrot-shaped nuclei with ill-defined scanty
cytoplasm.
• Tumour cells have a tendency to form linear chains, which infiltrate through cerebellar
cortex and aggregate beneath pia-subarachnoid space and eventually disseminate
through CSF.
• Rosettes may be centred by delicate argyrophillic fibrils of tumour cells.
• Tumour shows a prominent desmoplastic response.
Prognosis:
• Highly malignant but exquisitely sensitive to radiotherapy
• Extraneural metastasis to bone and lymph nodes common

Atypical Teratoid/Rhabdoid Neoplasm
• Malignant tumour of childhood (WHO grade IV/IV)
• Common locations include posterior fossa and supratentorial compartment
• Shows divergent differentiation into epithelial, mesenchymal, neuronal and glial com-
ponents
• Often shows rhabdoid cells as seen in rhabdomyosarcoma
Tumours of Meningeal Origin
Most common tumour of meningeal origin is a meningioma

Meningioma

• Constitutes 15% of all CNS tumours in adults and 3% of childhood tumours.

• Peak incidence in 5th to 6th decade; females are more commonly affected than males.
• Slow growing; develops from specialized arachnoid cells of villi that project into the
lumen of dural venous sinuses.
• Common locations: Superior sagittal sinus, sphenoid ridge, tuberculum sellae, olfactory
grooves, posterior cranial fossa and ventricles.
• Molecular genetics: Most common abnormality is loss of chromosome 22. Also seen are
deletions in the region close to but different from 22q12 that harbours NF2 gene.
Gross pathology:
• Well demarcated/unencapsulated
• Fixes to dura and buries itself in a cup-like bed; cerebrum practically never invaded
• Cut surface is whorled; haemorrhage and necrosis may be seen
• Rarely, calcification, ossification and cyst formation are observed

• Extends into muscles, air sinuses and orbit; may be associated with reactive hyperostosis

of bone
Histological types:
• Syncytial: Poorly defined polygonal cells arranged in sheets and tight groups; whorling
present (Fig. 23.2).
• Fibroblastic: Elongated cells with abundant collagen
• Transitional: Overlapping features of syncytial and fibroblastic type
• Psammomatous: Numerous psammoma bodies due to calcification of syncytial nests of
meningothelial cells
• Secretory: Characteristic PAS-positive intracytoplasmic droplets present
• Microcystic: Loose spongy appearance with microcyst formation
• Papillary: Papillary appearance (fibrovascular cores with pleomorphic cells around
them); high rate of recurrence
• Angioblastic: Vascular variant of meningioma

Note: Xanthomatous degeneration, osseous metaplasia and moderate nuclear pleomorphism

are common and usually of no prognostic significance in meningiomas.

Atypical meningiomas (WHO grade II/IV) are locally aggressive and have a higher rate of

recurrence. Histologically they show .4 mitoses/10HPF or at least three of the following

features:
Increased cellularity
1.
2.
High N/C ratio
mebooksfree.com