Subependymoma

Clinical History

A 41-year-old female patient presented with recurrent headaches but without any focal neurological symptoms.

Imaging Findings

Magnetic resonance imaging (MRI) of the brain with gadolinium revealed presence of a posterior fossa mass. The mass with a diameter of 8 x 13 x 17 mm was almost occluding the foramen of Magendie. It was well-defined, solid, quite homogeneous, slightly hypo-intense on T1-weighted images and moderately hyper-intense on T2-weighted images. No oedema or contrast enhancement could be delineated. The ADC was 1.2 x 10-3 mm²/s. No ventricular dilatation could be observed.
The patient underwent suboccipital craniotomy and complete macroscopic removal of the tumour. Postoperative tumour histopathology revealed the classical appearance of subependymoma WHO 1. At 1-year follow-up, MR imaging of the brain did not show tumour regrowth.

Discussion

Subependymomas were first described in 1945 [1] and are rare, low-grade, noninvasive tumours that occur most commonly in fifth and sixth decades of life. It was suggested that subependymomas may represent a hamartoma rather than a neoplasm, due to the slow proliferation [2]. 18% of subependymomas exhibited a mixed histological pattern and the most common mixture was subependymoma and ependymoma [3]. Many cases are found incidentally during autopsy. When symptomatic, subependymomas often obstruct critical portions of the cerebrospinal fluid pathway, causing hydrocephalus [4]. Most frequently subependymoma arise in the fourth ventricle, followed by the lateral ventricle and less frequently in the septum pellucidum and spinal cord [5].

On CT, subependymomas are well-defined, iso- to hypo-dense intraventricular mass lesions, with calcifications noted in up to 50% of the cases. Computed Tomography enhancement characteristics of subependymoma are variable [6].
MR characteristics include a well-demarcated solid or mixed solid and cystic intraventricular mass, hypo- or isointense on T1-weighted images and hyper-intense on T2-weighted images. The heterogeneous signal commonly seen in subependymomas correlates well with histopathological findings, including necrosis, calcification, tumour vascularity, microcystic structures or cystic spaces and chronic haemorrhage [7]. Usually there is no appreciable vasogenic oedema of the adjacent parenchyma. Subependymomas show no enhancement or mild-to-moderate enhancement.
Included in the differential diagnosis of ventricular masses are ependymoma, subependymoma, choroid plexus papilloma, metastasis, rarely meningioma, central neurocytoma and subependymal giant cell astrocytoma. The most challenging differential diagnosis of subependymoma in the fourth ventricle is an ependymoma. In the series of Hoeffel [7], all patients with subependymoma were older than 30 years, which narrows the differential diagnosis. The intraventricular or periventricular location and morphology do help in the differential diagnosis. Subependymoma is almost always totally intraventricular, whereas ependymoma commonly has a transependymal extension. Presence of oedema also seems to be a more common feature in ependymoma than in subependymoma [7]. The use of ADC values could be another hint in distinguishing cerebellar tumours. The reported ADC value of subependymoma is higher than those of ependymoma, but not as high as those of juvenile pilocytic astrocytoma [8].
MRI enhancement characteristics are variable, including absent to marked enhancement. Even when enhancement was present, it always was partial, in an irregular pattern with areas of nonenhancing solid tumour.

In cases of a completely intraventricular lesion in the fourth ventricle with no transependymal extension, which causes little or no oedema, and minimal or no enhancement is present, suspicion of subependymomas should arise.

Differential Diagnosis List

Final Diagnosis

Subepenymoma WHO grade I

URL:	https://www.eurorad.org/case/10651
DOI:	10.1594/EURORAD/CASE.10651
ISSN:	1563-4086