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 at our institution between 1990 and 1999. Full radiological and clinical follow-up was obtained in 29 (17 females, 12 males). Imaging was retrospectively reviewed, with particular attention to Computed Tomography (CT) and Magnetic 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 show better survival than other sites. Of 23 patients who had Tc99m-methylene diphosphonate (MDP) bone scans at diagnosis, four patients showed widespread 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 regions and 7.5 cm in the chest and abdomen. Tumours were typically of soft tissue density on CT with the larger (>5 cm) masses tending to be more heterogeneous in character. The lesions were slightly higher signal than muscle on T1-weighted (T1W) MRI and all masses were heterogeneous on T2W sequences. Calcification was uncommon (n = 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 bony invasion was seen in 12 patients at diagnosis. Metastases were identified in the lung (n = 5), pleura (n = 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. Tumours tend to displace rather than encase adjacent structures; local invasion occurred in 43%. Tumour calcification is uncommon. Poor prognostic features included the presence of distant metastases at diagnosis (all four patients with distant metastases at diagnosis died), but even patients without metastatic disease have a relatively poor prognosis.