Brainstem was, not long ago, considered as a
'no man's land'.
With recent advances in neuroimaging, and
surgical tools, there is a renewed interest in brainstem tumors among
All brainstem tumors do not behave in the
same manner. In the past, all tumors of the midbrain, pons, and medulla
oblongata were regarded as 'brainstem tumors'. Recently, it has been
suggested that there is a distinction between the thalamic and midbrain
lesions on the one hand and pons and medulla lesions on the other and that
the brainstem gliomas are not a homogeneous group with regard to their
clinical, pathohistological, or biological features and that their
prognosis may be directly related to tumor type and location.
Brainstem tumors are most commonly diagnosed
in children, in whom they account for 10% to 20% of the primary brain
Pilocytic astrocytomas account for 30% of all
infratentorial tumors in childhood, and 80% of pilocytic astrocytomas are
found in the posterior fossa. The reported increase in the incidence of
primary malignant brain tumors in children by 35% from 1973 to 1994,
appears to be brainstem tumor rates, which may due to advances in imaging.
Brainstem gliomas have been classified by
site, imaging, and pathology.
However, in clinical practice, they are
classified into diffuse, and focal ones; both may have exophytic growth.
The diffuse type accounts for
nearly 80% of them. The majority arising from and causing diffuse
enlargement of the pons. Axial and exophytic growth is also found in two
thirds of the cases. The medulla is often spared.They are infiltrative in
nature with relentlessly progressive. They present with short duration of
symptoms, usually consists of multiple bilateral cranial nerve deficits.,
long tract signs, and ataxia. Raised ICP and hydrocephalus are rare and
occurs in 10% of cases.
Histologically, they belong to fibrillary
astrocytomas, anaplastic astrocytomas, and glioblastoma multiforme.
Focal ones may be discrete
(<2cm in diameter) and exophytic variants. They
may be cystic or solid.
Cervicomedullary variants arise from
upper cervical cord, with typical rostal extension into the
cervicomedullary junction. The rostal extension is limited anteriorly by
the pyramidal decussations; thus the mass expands posteriorly at the level
of the obex and may rupture into the fourth ventricle. The caudal part is
identical to an intramedullary tumor. They usually present with lower
cranial nerve deficits, long tract signs, and occasionally torticollis.
The dorsal exophytic variants arise
from the floor of the fourth ventricle, usually filling it. Clinically,
there is marked by an insidious failure to thrive and signs and symptoms
of raised ICP in the young. Cranial nerve deficits are found in 50% of
them; but long tract signs are rare.
Histologically, they mostly belong to
Radiological findings associated
with low grade tumor include, the presence of exophytic protrusion
into the fourth ventricle through the dorsal brainstem and
cervicomedullary location, and surgery has been recommended.
On MRI, the focal tumors are small, well
circumscribed without associated edema or evidence of infiltration.
Cystic changes may occur. The diffuse ones are hypodense on TI and
hyperdense on T2.
Differential diagnosis include,
type with necrosis
focal: ependymomas, tuberculosis,
metastasis, lymphoma, abscess, vascular malformations, and infarction.
diffuse: vascular malformations,
demyelinating lesions, and encephalitis.
Some of them may disseminate. Neuroaxis
imaging and CSF analysis, if possible, have been recommended.
Surgery, despite all the
recent advances, has
limited role in diffuse ones.
Resection of well circumscribed, low grade
tumors has been shown to improve survival.
Cystic components, and focal tumor appearance
are thought to be favorable features for surgery.
Exophytic ones may be amenable for surgery;
patient selection is critical.
A midline suboccipital approach is commonly
preferred. Lateral exophytic ones may need a CP angle approach.
The floor of the fourth ventricle, or the
lateral brainstem in CP angle approach, is inspected for bulges and
Cyst, if any, should be aspirated .
Exophytic area, if any, is incised.
Methylprednisolone may be given just before incision, and continued for 24
hours (30mg/kg for the first hour followed by 5.4mg/kg/hr.
If no exophytic area is seen, one of the
'safe areas' is incised longitudinally, after mapping out eloquent areas
by direct electrophysiological stimulation of the cranial nerve nuclei.
Continuous intraoperative EMG monitoring from certain muscles of the head
is an alternative and can provide information about the status of the
respective cranial motor nerves.
The tumor is excised in piecemeal with
meticulous microsurgical techniques; recent tools, such as laser,
irrigation bipolar,and ultrasonic aspirator, facilitates tumor excision.
Tumor rim may be left behind, if there is no satisfactory cleavage is
In view of the wide variety of brainstem
lesions, a tissue diagnosis is warranted for appropriate treatment.
The use of open biopsy, and more
recently, image guided
biopsy has been advocated for tissue diagnosis. In addition, cyst, if
any, may be drained which will help symptomatically.
Stereotactic biopsy is indicated in focal
enhancing masses, especially when open surgery was not contemplated, for
Stereotactic procedures make use of
a transfrontal trajectory,
through the axis of brainstem, for biopsies of the diencephalon, midbrain,
and rostal pons, and
a suboccipital transcerebellar
trajectory, through the middle cerebellar peduncle, for biopsies of the
Steretactic biopsy is generally not advised
in dorsally exophytic tumors, cervicomedullary tumor, and focal midbrain
Open surgery has been suggested as a better
A stereotactic biopsy is unreliable in
diffuse non enhancing tumor. Diffuse ones has image characteristics which
are almost diagnostic, and the stereotactic biopsy, especially in
children, is not reliable in the diffuse variety. Direct radiotherapy is
acceptable without biopsy.
recommended as alternatives, in diffuse ones; the standard therapy has
been 55Gy to the tumor area with weekly dose of 800-1000 cGy.
Prognosis is generally poor in children.
Adults do better.
Small size, lack of diffuse appearance,
accessible location, and absence of preoperative neurological deficit
suggest favorable outcome. Some have questioned the value of surgery; they
claim the better prognosis is due to histology which is mostly pilocytic
in focal and exophytic variants.
Most authors agree that there is little
improvement in survival, with the attempted resection of a high grade
tumor, even though in specific instances current advanced techniques allow
for the performance of such surgery with acceptable morbidity.
Two year survival is reported to be 18% to
46% with radiotherapy in diffuse ones.
Chemotherapy, when added to radiotherapy
results a median survival of 44 weeks and a 1 year survival of 47%.
Other modes of radiotherapy do not add to it.
Experience with radiosurgery is limited. SRT is, usually, preferred.