Imaging of non-Central Nervous System Primitive Neuroectodermal Tumours: Diagnostic features and correlation with outcome

AIM: To document the varied radiological features before, during, and after treatment of non-Central Nervous System Primitive Neuroectodermal Tumours (PNETs), which are rare tumours of childhood. MATERIALS AND METHODS: Thirty-three children with PNETs have been treated a t our institution between 1990 and 1999. Full radiological and clinical fol low-up was obtained in 29 (17 females, 12 males). Imaging was retrospective ly reviewed, with particular attention to Computed Tomography (CT) and Magn etic Resonance Imaging (MRI). RESULTS: Age range at diagnosis was 0-16 years old (mean 4.4 years). There were five main sites of tumour: head and neck (n = 7), scapula/axilla (n = 2), chest (n = 11), abdomen (n = 3), and spinal/paraspinal (n = 6). Overall mortality was 62%. Tumours of the scapula or paraspinal region appear to s how better survival than other sites. Of 23 patients who had Tc99m-methylen e diphosphonate (MDP) bone scans at diagnosis, four patients showed widespr ead distant metastases, seven showed focal increased uptake in an adjacent bone only, and 12 had normal examinations. CT was performed in 25 patients and MRI in 20, both at diagnosis and follow-up. Average size of tumours at presentation was 4.5 cm in the paraspinal, head and neck and scapular regio ns and 7.5 cm in the chest and abdomen. Tumours mere typically of soft tiss ue density on CT with the larger (>5 cm) masses tending to be more heteroge neous in character. The lesions were slightly higher signal than muscle on T1-weighted (T1W) MRI and all masses were heterogeneous on T2W sequences. C alcification,vas uncommon (rr = 6) and generally sparse. Tumours tended to displace adjacent soft tissue structures such as vessels and bronchi rather than invade or encase them. Tumours rarely crossed the midline. Local or b ony invasion was seen in 12 patients at diagnosis. Metastases were identifi ed in the lung (n = 5), pleura tit = 2), brain (n = 4), bone (n = 4), lymph nodes (n = 2), liver (n = 2), subcutaneous tissues (n = 2), kidney (n = 1) and peritoneum (n = 1). CONCLUSIONS: Imaging characteristics of non-CNS PNETs are described. Tumour s tend to displace rather than encase adjacent structures; local invasion o ccurred in 43%. Tumour calcification is uncommon. Poor prognostic features included the presence of distant metastases at diagnosis tall four patients with distant metastases at diagnosis died), but even patients without meta static disease have a relatively poor prognosis. (C) 2001 The Royal College of Radiologists.