Thalamic glioma

Thalamic gliomas are very rare, deep-seated, generally high-grade glial neoplasms that form in the thalamus, representing 1–5% of all pediatric brain tumors.^[1] Because of their difficult to reach position, they are a unique and difficult challenge for neuro-oncologists and neurosurgeons.

Thalamic glioma
Specialty	Neuro-oncology, neurosurgery
Causes	Unknown
Prevention	Unknown
Treatment	Watchful waiting, radiation therapy, chemotherapy, resection
Prognosis	Two year survival rate 19.7% (adults), pediatric five year survival rate 15-25% (high grade astrocytoma) or 40% (low grade astroyctoma)

Diagnosis

Thalamic gliomas are most often discovered on magnetic resonance imaging following symptoms, with the most common presenting symptom being motor deficit.^[2] While a definitive diagnosis of the neoplasm cannot be made without a biopsy of the tumor, biopsies have historically been avoided due to the extreme sensitivity of the region.

Bithalamic glioma

A notable variant of thalamic gliomas are bithalamic gliomas. Bithalamic gliomas cross the interthalamic adhesion and occupy space in both thalami. These have poorer outcomes than unilateral thalamic gliomas.^[3]

Treatment

Unless a thalamic glioma shows aggressive behavior, they are often treated with a "watch and wait" approach until signs of growth occur.^[4] Thalamic gliomas can be treated with radiotherapy, chemotherapy, and/or resection.^[5]

Resection

Thalamic gliomas are among the most difficult challenges a neurosurgeon faces today. Historically, thalamic gliomas were considered inoperable.^[6] Advances in neurosurgical technology have opened up the thalamic area to resection, but conservative approaches remain popular.^[7] Microsurgical approaches are well suited for thalamic gliomas.^[8]

Prognosis

Thalamic gliomas have a poor prognosis. In adult patients, the overall two-year survival rate is 19.7%, with low grade tumors holding a two-year survival rate of 31.0% and high-grade tumors holding a two-year survival rate of 16.5%.^[2] In pedtiatric patients, low-grade astrocytomas held a five-year survival rate of 40% while high-grade astrocyte tumors held a five-year survival rate that varies between 15% and 25%.^[9] Strangely, pediatric thalamic oligodendrogliomas appear to have a far worse prognosis than thalamic astrocytomas, with a three-year survival rate of 14% in one series.^[9]

Higher Karnovsky performance status and CSF diversion^[10] are good prognostic markers in cases that match the criteria for glioblastoma.

While the H3K27m mutation that is the distinct marker of a diffuse midline glioma is generally a very poor prognostic factor, it is unusually associated with slightly higher rates of survival in adult thalalmic glioma patients.^[11]

Pathology

Thalamic gliomas are often but not exclusively diffuse midline gliomas; other varieties of glial tumor can develop in this region.^[2]

Prominent patients

• Tammi Terrell (1945–1970), Motown singer that died from an "acorn size" tumor in her thalamus^[12]