Thalamopeduncular syndrome

Thalamopeduncular syndrome (TPS) refers to a clinical presentation associated with lesions at the junction of the thalamus and cerebral peduncle. Primarily seen in pediatric patients (1-5% of brain tumors), it is often caused by low-grade gliomas (LGGs), such as pilocytic astrocytoma (PA) with KIAA1549-BRAF fusion or BRAF-V600E mutation. In adults, it may arise from vascular events like Artery of Percheron (AoP) occlusion leading to paramedian thalamopeduncular infarction.

Clinical presentation

• Tumoral TPS (Childhood): Progressive spastic hemiparesis, pyramidal signs, cranial nerve (CN) palsies (e.g., oculomotor), headache, ataxia, visual impairment, focal seizures, and hydrocephalus (HCP) due to ventricular obstruction.

• Vascular TPS (Percheron Type): Acute decreased level of consciousness (LOC), oculomotor disturbances, ataxic gait, hemiparesis, cognitive/behavioral changes, and rarely cervical dystonia.

Diagnosis

• Imaging: Brain MRI w/ gadolinium: Mixed solid-cystic lesions w/ heterogeneous enhancement; DTI for corticospinal tract (CST) mapping; nTMS for motor function. In vascular cases, MRI shows bilateral thalamic/midbrain infarcts.
• Histopathology: Confirms PA (Ki67 ~2%); molecular testing for BRAF alterations.
• DDx: Other thalamic/brainstem tumors, infarcts, or demyelinating diseases.

Treatment

• Surgical Management (Primary for Tumoral TPS): Goal: Maximal safe resection. Approaches: Transsylvian (most common), transcortical transtemporal, or parietal transcortical based on tumor location & CST displacement (antero-lateral/medial/posterior). Use IONM (SSEPs, MEPs, cortical-subcortical mapping). Outcomes: GTR in ~25%, STR in ~60%, PR in ~15%; reoperation for progression.
• Adjuvant Therapy: Chemo (carboplatin/vincristine) or RT for residual/aggressive tumors; targeted therapy (BRAF inhibitors) if mutated.
• Vascular TPS: Acute stroke management (thrombolysis if indicated); no routine neurosurgical intervention unless HCP requires VP shunt.

Prognosis and key points

• Tumoral: Favorable w/ LGG; mean FU 5+ yrs; ~40% disease-free, ~50% stable residual; mortality <15% w/ progression. Post-op neuro deficits may improve w/ rehab.
• Vascular: Variable; depends on infarct extent; potential for recovery but persistent neuro deficits common.
• Neurosurgical Pearls: Preoperative DTI/nTMS essential for CST preservation; balance resection vs. morbidity; monitor for HCP/progression.