Teaching Case

The patient was admitted to hospital because of an epileptic seizure. He had had absence seizures since the age of eight. MRI revealed a large mixed solid-cystic tumour with a solid mural nudule that involved the cortex and white matter of the left frontal lobe. A SPECT scan performed with technetium-99m HMPAO indicated tumour hypoperfusion.

The patient was admitted to hospital because of an epileptic seizure. He had had absence seizures since the age of eight.

MRI revealed a large mixed solid-cystic tumour, with a solid mural nodule that involved the cortex and white matter of the left frontal lobe. The solid portion of tumour was of inhomogeneous high signal intensity on T2-weighted images. The cystic portion was homogeneously hyperintense on T2-weighted images. A focal thinning of the calvarium related to very slow tumour growth was observed. Gadolinium-enhanced T1-weighted images showed marked enhancement of the nodule which was located eccentrically within the cystic mass.

A single-photon emission computed tomographic scan performed with technetium-99m hexamethyl-propyleneamine oxime (HMPAO) indicated tumour hypoperfusion.

At surgery, gross total resection of a large, lobulated, firm, greyish mass was achieved. Examination of slices disclosed proliferation of glial cells, most of which were astrocytes and large ganglion cells. Pathological findings were, therefore, consistent with ganglioglioma, WHO grade I.

Ganglioglioma is an uncommon tumour composed of a mixture of neuronal (ganglion) cells and glial tumour cells. These tumours comprise 0.4-6.25% of all primary brain tumours in adults and approximately 10% of all primary brain tumours in children (1).

Most gangliogliomas occur in children and young adults. Approximately 80% of patients are younger than 30 years of age, but the tumour may present at any age (2). There is no sex preponderance. Most become symptomatic during the second decade. Gangliogliomas are very slow-growing tumours. Symptoms have often been presents for years. A history of long-standing epileptic seizures, especially of complex partial seizures, is the most common presenting symptom, followed by signs of increased intracranial pressure.

Although gangliogliomas may occur in any location, the majority are supratentorial. The temporal lobe is the most common site, followed by the frontal and parietal lobes. The cerebellum is also a reported site.

These relatively low-grade neoplasms generally behave in a benign fashion and have a favourable prognosis. Complete resection leads to a good long-term prognosis. Malignant forms of ganglioglioma account for approximately 10% of cases. Malignant transformation usually occurs within the glial component of the neoplasm.

Gangliogliomas may be solid, cystic or mixed, and focal calcifications are common (30% of cases). Classically, ganglioglioma is described as a cystic mass with a mural nodule in approximately 40% of diagnosed cases.

The classic appearance on CT is a cyst with an iso- or hypodense mural nodule that is often calcified. However, gangliogliomas have variable density and contrast enhancement patterns, and calcification may be inconspicuous. Because these tumours are slow growing, peripherally located gangliogliomas may cause scalloped pressure erosion of the overlying calvarium (3).

On MR imaging, a well-defined cystic mass with a solid wall is typically seen, which is hypointense on T1-weighted and hyperintense on T2-weighted sequences. Enhancement varies from none to striking. Nodular, rim, and solid enhancement patterns all occur (3).

However, a solid mass showing non-specific low to intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images is also not uncommon. There is usually little associated mass effect or surrounding vasogenic oedema (4).

Ganglioglioma should be included in the differential diagnosis of intracranial masses when a relatively large cystic mass is present (preferentially located in the temporal lobes) that has little or no discernible solid components, has margins that enhance only slightly, and that at times contains dense and large calcifications or a solid, poorly defined mass is found in the temporal lobes that is generally hypodense by CT or of increased signal intensity on T2-weighted MR images.