Page 905 - Textbook of Pathology, 6th Edition

Most tumours are well-differentiated but anaplastic metastases to extraneural sites such as to lungs, liver, 889
variants are also recognised. vertebrae and pelvis.
Two variants of ependymoma deserve special
mention: myxopapillary type and subependymoma. MORPHOLOGIC FEATURES. Grossly, the tumour typi-
cally protrudes into the fourth ventricle as a soft, grey-
Myxopapillary ependymoma. It is a special variant of
ependymoma which is common and occurs in adults. white mass or invades the surface of the cerebellum.
Characteristically, it occurs in the region of cauda equina Microscopically, medulloblastoma is composed of small,
and originates from the filum terminale. True to its name, poorly-differentiated cells with ill-defined cytoplasmic
it contains myxoid and papillary structures interspersed processes and a tendency to be arranged around blood
in the typical ependymal cells. It is a slow-growing tumour vessels and occasionally forms pseudorosettes (Homer-
having a better prognosis. Wright rosettes). Another characteristic of the tumour is
differentiation into glial or neuronal elements.
Subependymoma. It occurs as a small, asymptomatic,
incidental solid nodule in the fourth and lateral ventricle
of middle-aged or elderly patients. Areas of microcysts OTHER PRIMARY INTRAPARENCHYMAL TUMOURS
and calcification may be encountered. Important examples of some other primary intraparen-
Histologically, it is composed of nests of uniform chymal are haemangioblastoma, CNS lymphoma and germ
ependymal cells in a stroma of very dense, acellular, finely cell tumours.
fibrillar background. Subependymoma is typically a very
slow-growing tumour. Haemangioblastoma
Haemangioblastoma is a tumour of uncertain origin and
Choroid Plexus Papilloma constitutes about 2% of all intracranial tumours. It is seen
Tumours derived from choroid plexus epithelium are more commonly in young adults and is commoner in males.
uncommon intracranial tumours. They are found in the It may occur sporadically or be a part of von Hippel-Lindau
distribution of the choroid plexus. In children, they occur syndrome (along with cysts in the liver, kidney, and benign/
most frequently in the lateral ventricles, whereas in adults malignant renal tumour). About a quarter of haemangio- CHAPTER 30
fourth ventricle is the most common site. They are invariably blastomas secrete erythropoietin and cause polycythaemia.
benign tumours and rarely ever undergo malignant
transformation. MORPHOLOGIC FEATURES. Grossly, the tumour is
usually a circumscribed cystic mass with a mural nodule.
MORPHOLOGIC FEATURES. Grossly, the tumour The cyst contains haemorrhagic fluid.
projects as rounded, papillary mass into one of the Microscopically, the features are as under:
ventricles. i) Large number of thin-walled blood vessels lined by
Histologically, choroid plexus papilloma is a papillary plump endothelium.
tumour resembling normal choroid plexus with a vascular ii) Vascular spaces are separated by groups of polygonal The Nervous System
connective tissue core covered by a single layer of cuboidal lipid-laden foamy stromal cells.
epithelium which lies upon a basement membrane.
Primary CNS Lymphoma
POORLY-DIFFERENTIATED AND
EMBRYONAL TUMOURS Lymphomas in the brain may occur as a part of disseminated
CNS tumours composed of primitive undifferentiated cells non-Hodgkin’s lymphoma (Chapter 14) or may be a primary
include medulloblastoma and glioblastoma, and rarely, CNS lymphoma. The incidence of the primary CNS
neuroblastoma (page 800) and retinoblastoma (page 512). lymphoma has shown a rising trend in patients of AIDS
Except for medulloblastoma, other examples of these and other immunosuppressed conditions. They occur in men
tumours have been described elsewhere in the text. above 5th decade of life. Primary CNS lymphoma has a poor
prognosis.
Medulloblastoma
MORPHOLOGIC FEATURES. Grossly, the tumour is
Medulloblastoma is the most common variety of primitive frequently periventricular in location and may appear
neuroectodermal tumour. It comprises 25% of all childhood nodular or diffuse.
brain tumours but a quarter of cases occur in patients over Microscopically, the features are as under:
the age of 20 years. The most common location is the i) Characteristically, the tumour grows around blood
cerebellum in the region of roof of fourth ventricle, in the vessels i.e. has an angiocentric growth pattern. Reticulin
midline of cerebellum, in the vermis, and in the cerebellar stain highlights this feature well.
hemispheres. Medulloblastoma is a highly malignant tumour ii) Typically, CNS lymphomas are diffuse, large cell type
and spreads to local as well as to distant sites. It invades with high mitotic activity.
locally and by the CSF to meninges, ventricles and iii) They are generally β-cell type.
subarachnoid space and has a tendency for widespread