Case of the Week

Background:

• Gangliogliomas are rare cerebral and spinal cord tumors in children. Histologically, gangliogliomas are mixed tumors, composed of relatively mature neoplastic glial cells, as well as of ganglionic cells, in varying proportions. Most of these tumors are classified as WHO grade I. High-grade anaplastic gangliogliomas and malignant transformation have seldom been reported. The temporal location is the most frequent, but gangliogliomas may also arise in the brainstem, cerebellum, and the spinal cord. BRAF mutations have been shown as a potentially targetable genetic abnormality in low-grade gliomas.

Clinical Presentation:

• Most gangliogliomas affect young adults and the pediatric population. Symptoms are reflective of tumor location. For instance, tumors within the cerebellum often cause headache, hydrocephalus, truncal ataxia, gait disturbance, and appendicular dysmetria.

Key Diagnostic Features:

• The MRI appearance of gangliogliomas may be grouped into 3 types: a cystic tumor, a solid-cystic tumor, and a solid tumor. Gangliogliomas are usually well-demarcated intra-axial lesions, both histologically and on imaging studies. They classically reveal themselves on MRI as cystic lesions, frequently associated with a mural nodule. This solid component is iso- or hypointense on T1 and hyperintense on T2. The enhancement of the solid portion is variable. The ganglioglioma may contain calcifications with blooming signal loss on SWI. CT may help identify calcification, which is commonly found in gangliogliomas.
• MR spectroscopy and perfusion MRI can help to differentiate gangliogliomas from gliomas. Cho/Cr ratios are lower in gangliogliomas than in gliomas and NAA/Cr ratios are higher. Higher cerebral blood volume values can help to differentiate gangliogliomas from other low-grade gliomas .
• Diffusion-weighted imaging with ADC values and perfusion-weighted imaging with CBV values can help to differentiate infratentorial ganglioglioma from pilocytic astrocytoma. Higher rCBV values and lower ADC values are seen in infratentorial ganglioglioma.
• Ganglioglioma dissemination does not correlate well with pathologic grade. Some gangliogliomas show a benign clinical course, but have leptomeningeal spread.

Differential Diagnoses:

Juvenile or adult gangliogliomas located in the cerebellum mainly need to be differentiated from the other cerebellar fossa tumors such as:

• Pilocytic astrocytoma: the most common cerebellar tumor in children. It can show necrosis and cystic changes. The fenestration of tumor capillaries causes marked enhancement. Higher ADC values and lower rCBV values are seen.
• Hemangioblastoma: composed of a cyst with nonenhancing wall and mural nodule with marked enhancement. This may have flow voids relating to blood vessels. The mural nodule has high rCBV ratios on MR perfusion imaging.
• Medulloblastoma: the second most common malignant brain tumor of childhood. This presents with heterogeneous signal on T2 due to the cystic and necrotic reorganizations, restricted diffusion, and heterogeneous enhancement.
• Ependymoma: usually arises from the floor of the fourth ventricle and squeezes out the foramen of Luschka.
• Glioma: Cho/Cr ratios are lower in gangliogliomas than in gliomas and NAA/Cr ratios are higher. Higher CBV values can help to differentiate gangliogliomas from other low-grade gliomas.

Treatment:

• Low-grade gangliogliomas may be cured surgically via a complete tumor resection. Meanwhile, radiotherapy is reserved for progressive or malignant tumors after surgical treatment.