Primitive neuroectodermal tumors: a clinical and radiological analysis of six cases

Primitive neuroectodermal tumor (PNET) is extremely rare and highly aggressive with poor prognosis. Few studies concerning PNET's the imaging features have been published.

Six cases of PNET, all confirmed by pathology and immunohistochemical (IHC) examinations, were treated during January 2012 to December 2016. These cases' clinical course and imaging findings were retrospectively analyzed.

Among six PNET cases, one located in left superior abdomen, one case at posterior abdominal wall, one case in right orbit, one case in left frontal temporal lobe, one case in pelvic cavity, and one case located in left supraclavicular fossa. The tumor's density was uniform for small tumor and heterogeneous for large tumors on CT images, while the size of tumors differed during presentation depending on the location of the tumor. Marked enhancement was visualized after injection of contrast media. The demarcation between the lesion and adjacent tissues or organs tended to be unclear. On magnetic resonance imaging (MRI) images, the mass mainly showed heterogeneously long T1 and long T2 signal intensity, mixed high signal intensity on fluid-attenuated inversion recovery (FLAIR) image. In two cases maximum intensity projection image reconstruction demonstrates tortuous blood vessels within the tumor on enhanced CT images. Five cases were treated by surgical resection with two cases received adjuvant radiotherapy and three cases received adjuvant chemotherapy. Six patients were followed up with a mean period of 34.5 months (ranging from 6 to 55 months). Five patients survived and one died. Among the five patients undergoing surgeries, one patient presented pelvic and abdominal recurrence/metastasis 2 months after abdominal PNET resection. One patient had a recurrent lesion in the right orbit involving the right ethmoid sinus 6 months after right orbital PNET resection. One patient's pelvic tumor recurred 7 months after PNET operation, and this patient died after 1 year and 10 months of follow-up. During the follow-up period, the remaining three cases did not show obvious recurrence and/or metastasis.

Overall, the imaging appearances of PNET lack characteristics. PNETs generally do not have clear boundary, or partially so, with its adjacent organs or tissues suggesting their invasive nature. Upon further validation, maximum intensity projection image reconstruction demonstrates tortuous blood vessels within the tumor on enhanced CT images may be valuable information for the diagnosis of PNET.