General
- A rare subtype of brainstem gliomas
- Frequently considered to be a benign subgroup of astrocytoma
- 4 principal types of tumour arises here:
- Astrocytomas
- Pilocystic astrocytomas are the most common
- Ependymomas
- Oligodendrogliomas
- Mixed gliomas (i.e., oligoastrocytomas)
Number
- Paeds
- Tectal gliomas make up less than 5 % of the brainstem tumors in children
- Adults
- Focal tectal tumors constitute 8 % of all brainstem gliomas
- Which in turn comprise 1 % of all the brain tumors in adults
- There is no difference in incidence of brain stem gliomas according to sex or gender.
- Mean age at the time of diagnosis was 7.7 years (standard deviation, 5.2 years)
Classification
Fisher et al. Classfication
- Pilocytic astrocytoma
- Fibrillary astrocytoma for brainstem gliomas
Oka et al classification:
- Based on the magnetic resonance (MR) appearance and correlated the findings with the neuroendoscopic, histopathological, and postoperative clinical findings.
Group 1
- MRI
- Bulbous tectal mass,
- Isotense on T1-weighted images
- Hypertense on T2-weighted images
- Does not have gadolinium enhancement.
- Neuroendoscopic findings
- Ill-defined mass in the cerebral aqueduct.
- Pathology
- Gliosis
- Outcome
- Complete resolution of symptoms
Group 2
- MRI
- An exophytic growth of the tectal mass into the cerebral aqueduct, extending into the diencephalon and midbrain tegmentum.
- Neuroendoscopic findings
- A wide orifice of the aqueduct is seen, with the protrusion of a soft, ill-defined, translucent, elastic mass. The posterior commissure was found to be deviated upwards.
- Pathology
- Benign astrocytoma
- Outcome
- Complete resolution of the signs and symptoms postoperatively.
Group 3
- MRI
- Large masses
- Mixed intensities on both T1- and T2
- Enhancement following gadolinium administration.
- Exophytic growth of the tumor into the cerebral aqueduct and third ventricle with oppression of the posterior diencephalon and midbrain tegmentum was identified.
- Neuroendoscopic findings
- A large, well-demarcated, hemorrhagic, globular tumor in the orifice of the aqueduct.
- It protruded into the cerebral aqueduct to extend into the third ventricle.
- Upward deviation of the stretched-out posterior commissure was noted.
- Pathology
- Anaplastic astrocytoma.
- Outcome
- Symptoms from the hydrocephalus were controlled, while those from the tumor persisted
Clinical presentation
- Increased ICP
- Papilledema
- Headache
- Nausea, and/or vomiting
- Gait ataxia
- Decline in school performance
- Parinaud’s syndrome
- Decreased vision
- Hemiparesis
- Diplopia
- Urinary incontinence
- Personality changes
Imaging
CT
- To show HCP
- Most predominant finding.
- Tectal tumors are usually small, appear isodense
- Show either limited or absent contrast enhancement
- Most cases in the past which relied exclusively on CT scans were misdiagnosed as congenital late-onset aqueductal stenosis
MRI
- Gold standard
- Characteristic appearance of tumor on MRI.
- Focal gliomas are well-circumscribed, isodense or hypotense on T1-weighted images
- Diffuse tumors tend to be hyperdense on T2-weighted images
- The radiological diagnosis of midbrain tumors is evident when they extend ventrally; however, for imaging pattern of ventrally exophytic tumors, it is difficult to distinguish from pineal tumors; it should therefore be included in the differential diagnosis
Diagnosis
- A definitive diagnosis requires the collection of a tissue specimen for histopathologic analysis.
- The diagnosis of benign tectal glioma is made based on the radiographic appearance and the indolent clinical course of the lesions
- According to reports from Fisher et al. [12], not all low-grade tumors are alike, and it is often difficult to distinguish pilocystic astrocytomas (grade I) from nonpilocystic astrocytomas (grade I) even after the histopathology has been determined.
- In such cases, the typical MRI pattern of non-enhancement on pilocystic tumors and enhancement of nonpilocystic tumors may be a means of distinguishing the two groups.
- Furthermore, some benign tumors will increase in size making further interventions necessary.
Management
Initially
- Control HCP with CSF diversion
- Aim to minimizing the signs and symptoms of increased intracranial pressure
- EVD
Conservative/palliative
- Generally indolent, clinically stable nature of the tumors.
- long-term monitoring with serial MRI imaging
Surgery
Aims
- Reduction of surgical mass
- To obtain a histopathological sample
Indication
- Cases demonstrating radiological tumor growth
- Cases demonstrating worsening symptoms due to tumour
- When definitive diagnosis is imperative
- Low grade lesion
- Treat HCP and survaillence
- ETV
- Endoscopic aqeuductoplasty
- High grade lesion
- Surgical resection
Endoscopic third ventriculostomy (ETV)
- Highly effective for the management of HCP in patients with tectal gliomas
- 70 % success rate in the treatment of aqueductal stenosis following the procedure
- Gold standard for tx HCP secondary to tectal gliomas
- A low morbidity and mortality,
- Lower chance of re-obstruction compared to the shunting
- Disadvantages
- Acute hydrocephalus secondary to re-obstruction
- Long-term follow-up involving periodic imaging, along with patient education addressing to prevent this
- Possible basilar artery damage
- Lack of longitudinal studies to determine the effectiveness
Endoscopic aqueductoplasty
- Involves
- Expansion of the CSF channel between the third and fourth ventricles.
- Allows for biopsy collection.
- Disadvantages
- Potential for iatrogenic tectal injury
Surgical resection
- Traditional approach to the management of tumors
- Not recommended for the management of tectal gliomas due to the indolent, nondestructive nature of the tumors.
- Indicated only if the tumor demonstrates
- Growth in size or
- A malignant, secondary, or vascular lesion is suspected.
- Approaches
- Supracerebellar–infratentorial midline approach
- Suboccipital craniotomy
- TPG may be difficult to remove due to the large volume and often inaccessible location
- Complications
- Postoperative Parinaud’s syndrome
- Impaired eye movements
- Auditory hallucinations
- Bilateral optic nerve atrophy
- Left hemianopsia (occipital lobe retraction)
- Death after being in a vegetative state
Radiotherapy
- To target a precise focal section with minimal damage to the surrounding structures.
- External radiotherapy has been found to be relatively successful with no side effects
- Focal radiotherapy was shown to provide good control of the tumor in rare, locally aggressive cases
- In adults, focal radiotherapy, along with peritoneal shunting, is associated with increased rates of long-term survival
- Cases treated with stereotactic radiosurgery have been reported to be effective; however, there was a reported extreme risk associated with a small increase in the dose
- The use of gamma knife in focal tectal tumors is still under investigation
Chemotherapy
- Along with radiotherapy may be attempted in cases where the complete removal of the infiltrating tumors is not possible.
- Chemotherapy protocol(s), however, must be reserved for patients demonstrating clinical deterioration
Prognosis
- Poor prognostic indicator
- Fewer than 6 months of symptoms before diagnosis;
- The presence of an abducens nerve palsy at time of presentation,
- Engulfment of the basilar artery,
- Pontine location.
Differential diagnosis
- Aqueductal stenosis
- No mass lesion
- A focal stenosis or web may be visible
- With larger lesions, where the mass is not definitely arising from the tectal plate then the differential is essentially that of a pineal region mass and therefore includes:
- Pineal parenchymal tumours and germ cell tumours
- Pineal cyst
- Meningioma
- Cerebral metastasis
- Cavernous malformation
- In patients with NF1 a hamartoma should also be considered. They tend to have some T1 hyperintensity 4
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