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Many
surprises may await a surgeon, when the pathologist comes up with the
'verdict'.
These
pathological curiosities do not have any specific clinical or
radiological feature. They behave like any other intracranial tumor.
Some
of them, which are not grouped in other brain tumor categories, are
listed below.
The
list is, by no means, complete.
1)
Intracranial Sarcomas:
These
are rare, accounting for less than 1% of all intracranial tumors, usually
occur in infants and the young children.
The
primary sarcomas arise from mesenchymal tissue. It may be
diffuse meningeal sarcomatosis, arising from meninges or intraparenchymatous,
arising presumably from the mesenchymal tissue associated with blood
vessels, tela choroidea, or choroid plexus.
The
cause is unknown. Prior intracranial radiotherapy may be a cause in some.
Sarcomas following radiation to for pituitary tumors have been more
frequently reported. The reported median time for development of sarcoma
is about 10 years.
Clinically,
radiologically, and at surgery, they mimic any other high grade
intracranial tumors.
The
diagnosis is by histology using reticulin stain and PTAH and the
birefringence test.
Surgical
resection is the primary mode of treatment. The exact role of
radiotherapy and chemotherapy have not been established.
Prognosis
for survival is generally poor.
Local
recurrences are common. Distant metastases are rare.
Fibrosarcomas
are the most common intracranial sarcoma, and may
affect either the dura or the brain parenchyma. Cerebellar sarcomas can
occur and mimic medulloblastomas, especially in adults. A careful search
for a primary systemic sarcoma is in order before a diagnosis of primary
intracranial sarcoma is made. In addition, sarcomatous degeneration of a
meningioma, and a gliosarcoma need to be ruled out. Immunohistochemistry
may help.
Chondrosarcomas
arise from the dura, and skull base. rarely, intraparenchymal ones are
reported. Fourth ventricle and falx chondrosarcomas have been reported.
Histologically, the cartilage elements are less well developed.
Mesenchymal
chondrosarcoma has been
reported as a primary neoplasm of the dura in the young and the middle
aged. Prior trauma has been blamed. They are usually attached to the dura
in either the cranial vault or the spinal canal. they tend to
recur, and may metastasize.
Rhabdomyosarcomas occur
more frequently in the posterior fossa and in the midline where they
mimic medulloblastoma, and occasionally arise in the leptomeninges. They
can form a part of germ cell tumors.
The
diagnosis is aided by immunohistochemistry.
Giant cell
sarcomas is a controversial
pathology. Many regard them as a variety of gliosarcoma. They are well capsulated and are removed
easily at surgery.
Malignant
Fibrous Histiocytomas are more common in
adults, and can arise in the dura and less commonly from intraparenchymal
source.
Angiosarcomas
account for less than 1% of all sarcomas, and usually arise in the skin.
Occasionally, they arise from intracranial vessels.
Sarcomatous
metastases can occur from a systemic sarcoma.
According to the current literature, 10-15% of all osteosarcoma patients
experiencing relapse may bear risk for CNS metastases. Osteosarcoma may
develop years after radio surgery for a benign brain neoplasm.
2) Rosai Dorfman
Disease (RDD) of the Central Nervous System:
It is an idiopathic,
non-neoplastic, lymphoproliferative disorder. Usually presenting with
bilateral painless cervical lymphadenopathy. Primary Rosai-Dorfman
disease of the CNS is uncommon. Only 34 cases with primary CNS RDD have
been reported.
Imaging reveals
dural-based, contrast-enhancing masses that often elicit vasogenic edema
in the underlying brain.
Clinically & radio
logically, they simulate a meningioma, and can be misdiagnosed as a
nonspecific inflammatory process.
Histological and
immunohistochemical confirmation is essential for a definitive diagnosis.
Surgical excision gives
a good result (no recurrence or growth being reported).
The role of
radiotherapy & chemotherapy including steroid is controversial.
3) Polar
Spongioblastoma:
Polar
spongioblastoma has been now deleted from the current WHO classification
since it is considered a growth pattern rather than a clinicopathological
entity. Traditionally, they are considered as rare midline
tumors of children of unknown origin. The hypothalamus, lateral walls of
the third and fourth ventricles, and optic chiasma are most commonly
involved.
The presentation is
usually with seizures and focal diencephalic syndrome depending on the
location.
CT reveals a hypodense
lesion with areas of calcification. No MRI data is available.
Histologically, the
tumor cells are arranged in characteristic parallel fashion, like a step
ladder, forming compact bands secondary to palisading of the nuclei.
They are mostly GFAP
negative and GHA positive, suggesting a primitive glial precursor origin.
The treatment is
surgery, and radiotherapy in subtotal resection. The outcome is generally
favorable.
4) Solitary
Plasmocytomas:
They may occur primarily
inside the cranial cavity without involvement of skull or at other
systems. Most of them have a dural attachment. They can occur in the
third ventricle or in the posterior fossa. Histological features
are that of a myeloma.
After excision, and
irradiation, the patient is cured and free of symptoms.
5) Lipoma:
Slow growing lesion
resulting from a defective closure of the developing neural tube; many
lipomas are associated with other major congenital anomalies, and are
incidental findings in CT/MRI scans. The tumor is sharply circumscibed,
often adherent to its surroundings and consists of mature adipose
tissue. Preferred intracranial locations are corpus callosum,
quadrigeminal plate and infundibular region.
Spinal
lipomas are distinct collections of fat and connective tissue that are at
least partially encapsulated and have a definite connection with the
spinal cord. Spinal lipomas are the most common type of occult spinal
dysraphism and account for some 35% of skin-covered lumbosacral masses.
Typically, the mass lies in the midline just cephalic to the intergluteal
crease, and extends caudally, asymmetrically, into one buttock.
6) Fibroma:
They have been reported
in infants and the young. Ossifying fibroma of the anterior cranial fossa
invade the orbit, the paranasal sinuses, and the maxillary antrum. The
differential diagnosis include meningioma and fibrous dysplasia.
The pathogenesis is not
clear.
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