Second edition

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598 Brain tumors and hydrocephalus
Figure 19.1 A sagittal T1-weighted magnetic resonance scan
demonstrates the clear demarcation between a meningioma and
the surrounding tissue. (Reproduced from Gillespie and Jackson
2000.)
diffusely increased signal intensity in the white matter,
which may undergo enhancement.
Oligodendrogliomas arise from oligodendrocytes and
are indolent growths (Wilkinson et al. 1987) found typically
in the white matter of the frontal or temporal lobes,
which often present with seizures; on MR scanning they
present as non-enhancing masses with increased signal
intensity on T2-weighted images, and on CT scans one may
appreciate calcification.
Ependymomas, although most commonly seen in children,
may present in early adult years. These tumors arise
from ependymal cells of the fourth, third, or lateral ventricles,
and may cause symptoms either by causing obstructive
hydrocephalus or by extending into the adjacent brain
parenchyma; they may undergo calcification and may
show enhancement.
Meningiomas are very slow growing tumors that arise
from arachnoidal cells and which have an attachment to
the dura. These are well-demarcated, extra-axial tumors
that produce symptoms by compression of the subjacent
brain parenchyma, from which they are clearly separated,
as illustrated in Figure 19.1. Although they may or may not
be readily discernible on T2-weighted scans, they do
undergo homogenous enhancement. There are several
favored locations. Meningiomas of the falx cerebri, by
compression of the medial aspects of the frontal or parietal
cortices, may cause dementia or paraparesis. Lateral convexity
meningiomas may cause various focal signs, such as
hemiplegia or aphasia. Olfactory groove meningiomas may
cause anosmia, blindness, and, by upward extension
against the frontal lobe, dementia; should they attain a size
capable of causing increased intracranial pressure,
a Foster Kennedy syndrome may occur, with ipsilateral
anosmia, ipsilateral optic atrophy, and contralateral
papilledema. Suprasellar meningiomas may cause a bitemporal
hemianopia and pituitary failure, and meningiomas
of the sphenoid ridge may present with extraocular nerve
palsies and proptosis. All meningiomas may also be associated
with seizures. Rarely, rather than presenting as a circumscribed
mass, meningiomas may present ‘en plaque’ as
a sheath-like structure.
Primary central nervous system lymphoma, once rare, has
recently shown an increasing incidence, and this appears to
be the case not only in immunocompromised patients, such
as transplant patients (Schneck and Penn 1970) and those
with AIDS (Feiden et al. 1993; Lang et al. 1989), but also in
immunocompetent elderly patients. These tumors may be
single or multiple and typically show bright, homogenous
enhancement (Lai et al. 2002). Although most are found in
the cerebrum, often in a periventricular location, they may
also occur in the cerebellum or brainstem. They often seed
into the cerebrospinal fluid (CSF), and a suspicion of
primary central nervous system lymphoma is one situation
where a lumbar puncture should be seriously considered.
Neuromas, although capable of arising from cranial nerves
V, VII, IX, or X, are by far most commonly associated with
cranial nerve VIII, in which case they are referred to as
acoustic neuromas. These acoustic neuromas constitute
the most common cause of a cerebellopontine angle tumor
and typically present with hearing loss, accompanied in
most cases by dysequilibrium and tinnitus; with growth of
the tumor and compression of cranial nerves V and VII,
there may be facial numbness and a peripheral facial palsy;
rarely, a trigeminal neuralgia may occur (Harner and Laws
1983). In cases in which the cerebellum is compressed,
there may be nystagmus and ataxia.
Medulloblastomas, although generally seen only in children,
may occasionally occur in adults. These are typically
found in the midline cerebellum and often protrude into
the fourth ventricle, causing hydrocephalus.
Gangliocytomas (Kernohan et al. 1932) are composed of
neural elements, and gangliogliomas (Morris et al. 1993) of
both neural and glial elements. These are rare, indolent
tumors, generally found in the temporal, frontal, or parietal
cortices, which typically present with seizures.
Pituitary adenomas may be subclassified according to
either their size or their endocrinologic status. Macroadenomas
are larger than 1 cm, whereas microadenomas,
which are more common, are smaller. Endocrinologically,
more than 80 percent of adenomas are secretory, with the
remainder being non-productive. Pituitary adenomas may
cause symptoms by either compression of adjacent tissue
or secondary to the secretion of various hormones. With
compression of adjacent pituitary tissue there may be
pituitary failure, with, for example, hypothyroidism or
adrenocortical insufficiency. Lateral extension of a
macroadenoma into the adjacent cavernous sinus may
cause an oculomotor palsy or facial numbness in the areas
of the first or second divisions of the trigeminal nerve.