Case of the Week

Background:

• Diffuse leptomeningeal glioneuronal tumor (DLGNT) is a rare entity, first included in the WHO Classification of Brain Tumors in 2016.
• DLGNT has a predilection for the pediatric population.
• Histologically, it is characterized by low to moderate density of bland, monomorphous oligodendrocyte-like cells with round nuclei, fine chromatin, and inconspicuous nucleoli in a desmoplastic or myxoid leptomeningeal stroma.
• On immunohistochemistry, tumor cells are positive for S-100 and Olig2.
• KIAA1549-BRAF fusion and 1p deletion are common molecular findings.

Clinical Presentation:

• The most common clinical manifestations include headache and vomiting.
• Seizures and focal neurologic deficits may also be seen.

Key Diagnostic Features:

• Diffuse enhancing nodular leptomeningeal thickening, especially at the basal citerns and the interhemispheric fissure
• Nonenhancing T2 hyperintense, cystic lesions along the leptomeningeal surface, which typically do not show diffusion restriction
• Hydrocephalus
• Parenchymal lesions may be present due to spread along Virchow Robin spaces
• Spinal involvement: nodular leptomeningeal thickening, intramedullary spinal cord mass, and multifocal cystic spinal cord lesions

Differential Diagnoses:

• Tuberculous leptomeningitis: Diagnosis is based on clinical, imaging, and most important, biological features. The most common imaging features are basal meningeal enhancement and hydrocephalus. Tuberculomas are seen as well-defined and nodular or oval shaped intra- or extra-axial lesions.
• Racemose cisternal neurocysticercosis: Typically lacks a scolex and may appear as multilobulated cysts in the basal cisterns and subarachnoid spaces.
• Leptomeningeal carcinomatosis: Linear leptomeningeal enhancement in a patient with cancer history.
• Neurosarcoidosis: usually occurs in the third and fourth decades of life. The leptomeningeal involvement is seen as diffuse and nodular thickening and enhancement that can also spread along the perivascular spaces. Other imaging findings, such as enhancing or nonenhancing intracranial and spinal mass lesions, may also be seen.

Treatment:

• There are no established guidelines for treatment.