A Case of a Primitive Neuroectodermal Tumour in a 2 year old

Clinical History

A 2-year-old girl presented to hospital with a 1-week history of right upper limb weakness and choreiform movements and a 1-day history of right lower limb weakness and right facial droop.

Imaging Findings

Multisequence imaging of the brain and spine was performed. Sequences included axial T2, axial T2 FLAIR, axial diffusion, sagittal T1, and sagittal and axial T1-weighted imaging post gadolinium. There was a large mixed solid and cystic mass in the left cerebral hemisphere measuring 8.5 x 6.7 x 6.9 cm. It was predominantly cystic, especially superiorly where a dominant cyst was seen (Fig. 1). Numerous smaller cysts were identified in the periphery. There was a solid component noted inferiorly (Fig. 2), which enhanced uniformly and avidly after gadolinium (Fig. 3). A blooming artefact on the gradient image was suggestive of calcification or haemorrhage within the tumour (Fig. 4). There was midline shift and effacement of the sulci in the left frontal and parietal lobes. The overall impression was that of a large supratentorial mixed solid cystic tumour with calcification and enhancement of the solid components associated with significant mass effect and midline shift.

Discussion

The term "Primitive Neuroectodermal Tumour" (PNET) was introduced in 1973 to describe a group of tumours composed of undifferentiated or poorly differentiated cells [1]. Since then, classification issues have been particularly controversial, especially concerning the question whether PNETs arise from a multipotent cell unique to the particular involved area of the CNS, or from a primitive cell common to all sites. According to recent WHO classifications, central PNETs are a subtype of “embryonal tumours”, and thus separated from medulloepitheliomas and ependymoblastomas. Some PNETS can be classified according to specialised tissue of origin (e.g., retinoblastoma or pineoblastoma), but most of the remainder originate in the cerebral hemispheres or suprasellar region and were previously referred to as "supratentorial" PNETs. Central PNETs in children represent less than 2.5% of childhood brain tumours [2]. 80% are diagnosed before the age of 10 years, and 25% present within the first two years [3]. Older children with PNETs typically have signs of increased intracranial pressure, while infants present with lethargy, irritability, anorexia, and/or an enlarging head circumference. PNETS also may be congenital and should be considered a likely diagnosis when a large, heterogenous neoplasm of the cerebral hemispheres that shows malignant neuroradiological features is found in infants. Leptomeningeal metastases are found in 10%-50% of cases at the onset [4]; therefore, spinal MRI is mandatory preoperatively to stage disease and tailor treatment. The tumour typically appears as a large hemispheric mass with sharp, irregular margins and markedly inhomogeneous structure due to marked cystic-necrotic degeneration, calcification and haemorrhage [5]. MRI demonstrates heterogeneous enhancement with hypointense regions correlating to haemosiderin or calcification. T1 hyperintense regions correspond to haemorrhage and T2 bright regions reflect cystic components. The ideal treatment of PNETs utilises a combination of aggressive surgery and radiation therapy (RT) to the neuraxis [3]. Adjuvant chemotherapy may further improve survival, but the optimal chemotherapy approach is unknown. While histologically very similar to medulloblastomas, PNETs are thought to be less curable [6]. Therefore, higher doses of RT are used for treatment, regardless of staging. Management of infants and children ≤3 years of age, who are at high risk for severe neurologic impairment if their initial treatment includes craniospinal RT, is particularly challenging [5]. Despite aggressive combined modality treatment, recurrence is fairly common, often occurring in the early post-treatment phase. The reported three-year survival rate has ranged from 57% to 73% with regimens that include radiation [6, 7]. Children younger than three years and patients with pineal PNETs have the poorest prognoses [3].

Differential Diagnosis List

Final Diagnosis

High grade central primitive neuroectodermal tumour (PNET)

URL:	https://eurorad.org/case/12451
DOI:	10.1594/EURORAD/CASE.12451
ISSN:	1563-4086