Low-Grade Gliomas (LGG)
Description
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Tumours of the CNS are a diverse group, including low-grade gliomas (LGG), high-grade gliomas, ependymomas, embryonal tumours, and pineal region tumours.
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CNS tumours are the second most common paediatric cancer worldwide, after acute lymphoblastic leukaemia.
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In Zambia, they rank 10th in incidence (Globocan 2020).
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LGGs comprise the majority of childhood brain tumours, most commonly arising in the posterior fossa (15–25%), cerebral hemispheres (10–15%), and optic pathways.
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Most LGGs are sporadic, but some occur within cancer-predisposition syndromes such as Neurofibromatosis type 1 (NF1) and Tuberous Sclerosis Complex (TSC).
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LGGs are slow-growing, generally benign histologically, and associated with high long-term survival, though low but steady progression may occur even 10 years after diagnosis.
Classification (WHO Grading, Histology)
| Tumour Type | Grade I | Grade II |
|---|---|---|
| Astrocytic tumours | Pilocytic astrocytoma, Subependymal giant cell astrocytoma | Diffuse astrocytoma, Pilomyxoid astrocytoma, Pleomorphic xanthoastrocytoma |
| Oligodendroglial tumours | Oligodendroglioma | – |
| Neuronal & mixed neuronal-glial tumours | Ganglioglioma, Gangliocytoma, Desmoplastic ganglioglioma, Dysembryoplastic neuroepithelial tumour | Oligoastrocytoma |
Signs and Symptoms
General symptoms (from increased intracranial pressure):
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Headaches
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Nausea and vomiting (especially morning)
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Lethargy
Older children:
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Abnormal pupil response
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Sixth cranial nerve palsies
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Papilledema
Infants / Young children:
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Irritability
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Anorexia / failure to thrive
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Developmental delay or regression
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Macrocephaly, separated cranial sutures
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Bulging anterior fontanelle, shrill cry, or “setting-sun” eye sign
Specific symptoms (localizing):
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Cerebral hemispheres: Seizures, hemiparesis, behavioral changes
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Optic pathway gliomas (OPTs): Decreased visual acuity, optic nerve atrophy, proptosis, strabismus
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Brainstem tumours: Lower cranial nerve deficits (dysphagia, dysarthria), abnormal breathing, hemiparesis, spasticity, hyperreflexia, Babinski sign
Investigations
Radiology is cornerstone:
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CT scan of the brain: pre- and post-contrast
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MRI of brain (with and without contrast)
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Initial spinal MRI if feasible (spinal metastases in ~10% of cases)
Biopsy:
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For unresectable LGGs when diagnosis is uncertain
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OPTs are generally not routinely biopsied
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Some LGGs can be diagnosed reliably with imaging alone, but accurate pathological confirmation is essential if uncertain
Treatment
Supportive / Surgical
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Surgery is primary treatment where gross total resection is possible
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Tumours in deep midline supratentorial regions, optic pathway/hypothalamus, and brainstem: refer to regional/national centre for expertise
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>95% resection: monitor with MRI every 4 months for 3 years, then extend intervals as convenient
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Review plan if patient worsens clinically or tumour increases in size
Non-resectable / High-risk locations
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Chemotherapy: children <3 years, deep/sensitive structures, or progressive disease after radiation
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Radiotherapy: inoperable, recurrent, or progressive tumours; for children >3 years with visual compromise; generally avoided in OPT/NF1 due to vascular and endocrine risks
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Observation: small tumours, NF1 patients; close MRI monitoring
Chemotherapy – CbV Regimen
Induction Phase (10 weeks):
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Carboplatin: 175 mg/m² IV over 1 hour, 8 doses
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Vincristine: 1.5 mg/m² IV push (max 2 mg/dose), weekly for 10 doses
Maintenance Phase (up to 8 cycles):
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Same drugs as induction
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Begins 2 weeks after last induction cycle
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Given if objective response or disease stabilization