CASE REPORT 18 SA JOURNAL OF RADIOLOGY • March 2006 Primitive neuroectodermal tumours (PNETs) are tumours from plu- ripotent neural crest cells1-5 and may occur in the central or peripheral nervous system.4 PNET must be distinguished from other small round cell tumours like Ewing’s sarcoma (ES), extraosseous Ewing’s sarcoma, neuroblastoma, lymphoma, rhabdomyosarcoma and small-cell carcino- ma.3,4,6,7 Although it can occur at any age, PNET occurs more frequently in adolescents and young adults,2,3,6 with a median age of 17 years.3,6 Case report A 20-year-old black woman presented with a 3-month history of lower back pain, a 2-week history of paraplegia and paraparesis, and 1-week history of loss of sphincter control. A supine chest radiograph (CXR) showed a large mass in the right hemithorax (Fig. 1); this posterior mass could be confirmed on the lateral lumbar spine X-ray. The T11 inter- pedicular distance was increased and the pedicles were flattened on the anteroposterior (AP) lumbar spine X-ray. Computed tomography (CT) (Fig. 2) and magnetic resonance imaging (MRI) (Figs 3 - 5) showed a well-defined lobulated paraspinal mass in the right hemithorax mea- suring 18 x 11 x 16 cm. The mass involved most of the lower chest cavity and extended into the spinal canal displacing and compressing the spinal cord anteriorly and to the left (Figs 3 and 4) and expanding Paraspinal primitive neuroectodermal tumour (PNET) of the chest C Minné, MB ChB, Dip EC (SA) N Khan, MB BS, FCRad (D) SA Department of Diagnostic Radiology, University of Limpopo, Medunsa Campus CASE REPORT 18 SA JOURNAL OF RADIOLOGY • March 2006 Fig. 1. A supine CXR shows a large mass in the right hemithorax. Fig. 2. The post-contrast CT image through the lower chest and upper abdomen demonstrates heterogeneous enhancement of the mass. Fig. 3. This T1-weighted axial image shows a right paraspinal mass isoin- tense to muscle. Haemorrhage can be seen as a hyperintense area in the mass. Invasion of the chest wall and erector spinae muscles is seen on the right. The mass extends into the spinal canal via the intervertebral foramen with subsequent widening of the foramen. The spinal cord is compressed and displaced anteriorly and to the left. CASE REPORT paraspinal.indd 18 3/27/06 12:25:52 PM the intervertebral foramina (Figs 3 and 4). The superior portion of the mass had a large cystic component (Fig. 5). The diaphragm could be seen clearly and was displaced antero-inferiorly by the mass, which was seen superiorly to it (Fig. 5). No infiltration of the diaphragm could be demonstrated. The right kidney was subsequently also displaced antero- inferiorly. Infiltration of the chest wall and erector spinae muscles was well demonstrated on both CT and MRI (Figs 3 and 4). The right ribs were splayed and intervertebral foraminae widened but no bony erosion was seen. No calcification was demonstrated on either CT or MRI, but haemorrhage was seen on MRI (Figs 3 and 4). Regional lymphadenopa- thy was not seen. The lesion was hypodense to muscle (26 HU) on CT and showed inhomogeneous enhancement post contrast (Fig. 2). On T1-weighted images the mass was isointense to muscle (Fig. 3) and enhancement post gadolinium was heterogeneous (Fig. 5). T2-weighted images showed a hyperintense mass and the cystic component was well demonstrated (Fig. 4). No lung or bony metastases were seen on CT and Tc 99m-MDP bone scan respectively. At surgery an extradural mass was found. The spinal canal was decompressed and a laminectomy was per- formed on T10-L1, and pedicular screws were inserted to stabilise this region. Histological examination revealed a tumour of small round cells with hyperchromatic nuclei and pale to clear cytoplasm. A few Flexner- Wintersteiner rosettes were seen. Immunohistochemistry revealed the following: S100 was diffuse strong positive, vimentin was positive, CD99 had focal positivity, and chromogranin, synaptophysin and cytokeratin were negative. The diagnosis of PNET was made. The patient was started on a multidrug chemotherapy regimen. Although follow-up scans were done early after treatment the response to chemotherapy was poor with hardly any reduction in tumour size after 3 months. Discussion PNETs are very rarely seen in the black population3 and comprise 4% of soft-tissue tumours2 Peripheral primitive neuroectodermal tumours (pPNET) is a group of poorly differentiated small round blue cell tumours from neural crest origin.1-4,6 PNET and ES are classified together into the Ewing family of tumours,2,6 which is comprised of tumours with poorly differentiated small round cells.2,6 PNET is dis- tinguished by neural differentiation,2 seen as Homer-Wright rosettes4-7 or Flexner-Wintersteiner rosettes.4,7 Immunohistochemistry is used to detect expression of at least 2 of the following neural antigens in order to make the diagnosis of PNET, namely neuron-specific enolase (NSE), protein S100, Leucine 7, and neurofilaments protein, chromogranin A or synaptophysin.6,7 A highly specific antibody, CD99 (MIC2), can be found in both PNET and ES with immunostaining.5,7 PNET is seen mostly in the thoracopulmonary region and is also known as Askins tumour when it is in the chest wall.2,3,6,8 Other sites are the kidney, retroperitoneum/ paraspinal, head and neck region.2 Uncommon sites are the uterus, ovary, bladder, testis, pancreas, parotid, skin, subcutaneous tissues, lung, adrenal glands, dura mater and small bowel.2 These tumours are rapid-growing masses but regional lymphade- nopathy and metastases are uncommon. When they metastasise they tend to go to bone and lungs1-3,6,8 more often. The next most com- mon sites documented are bone marrow,2,6 lymphnodes1 and brain.8 Metastases have also been described in the liver,2 mediastinum3 and chest wall.3 Imaging modalities used are CT, MRI and nuclear medicine. CT and MRI are done to demonstrate the size and extent of the lesion.2 Soft tissue invasion can be demonstrated well on both modalities.8 CT showed soft tissue invasion just as well as MRI in several cases8 and dem- onstrated bony erosion and lung metastases better than MRI,8 but MRI is the best modality to demonstrate spinal cord involvement. In our case CASE REPORT Fig. 4. A T2-weighted image on the same level as Fig. 3 shows a hyperin- tense heterogeneous mass. The invasion of the chest wall and spinal canal with widened intervertebral foramen and displaced spinal cord is clearly seen. Fig. 5. A coronal post-contrast T1-weighted sequence. The mass enters the spinal canal via numerous neural foramina. 19 SA JOURNAL OF RADIOLOGY • March 2006 paraspinal.indd 19 3/27/06 12:25:52 PM CASE REPORT 20 SA JOURNAL OF RADIOLOGY • March 2006 the diaphragm was demonstrated more clearly on the MRI sequences and infiltration of the diaphragm could not be excluded on CT. Another important role of CT or MRI is to determine resectability and to detect metastases.2,3 They are also used in follow up to determine response to treatment2 and to detect recurrences. TC 99m-MDP (bone scan) is of value in detecting distant bony metastases8 and 8 F-fluoro-2-deoxy-glu- cose (FDG)-position emission tomography (PET) scan can be used to detect recurrence of intraspinal PNET.1,9 CT The CT picture is usually of heterogeneous soft tissue density.2,3 The mass can be isodense or slightly hypodense to muscle3 and larger tumours commonly have hypodense necrotic/cystic areas.2,3,6,8 Post-con- trast enhancement is mostly inhomogeneous.3,6,8 Calcifications are seen in less than 10% of cases, but could be faint and speckled or stippled.6,8 Haemorrhage can be seen as a hyperdense area in the mass if present. Regional lymphadenopathy is rarely seen but chest wall invasion is more common and would be evidenced by pleural effusion, bony destruction, tumour nodules in the muscles and abnormal enhancement of the chest wall.8 MRI MRI T1-weighted images would show a mass isointense or slightly hyperintense to muscle2,3,5,6,8 with low-intensity areas correlating to cys- tic/necrotic areas in the tumour and hyperintense areas correlating to haemorrhage. Post-gadolinium enhancement may be seen uniformly or inhomogeneously.2,3,5,6,8 Heterogeneous high signal intensity is typically seen on T2-weighted images;2,3,5,6,8 this sequence usually demonstrates the cystic components best. A STIR sequence would also demonstrate a heterogeneous high signal intensity mass.3,6 Conclusion PNETs are aggressive neoplasms and should therefore be diagnosed accurately and as early as possible. The distinction between PNET and ES cannot be made radiologically and could even be difficult on histological examination. Neural differentiation, immunostaining and immunohistochemistry can help to distinguish these tumours. Unfortunately a standard therapy does not exist yet and patients are offered a combination of surgery, chemo- and radiotherapy. Prognosis depends on the location of the tumour but PNET has a generally poor prognosis. Alternative treatment should be investigated further. 1. Virani MJ, Jain S. Primary intraspinal primitive neuroectodermal tumor (PNET): a rare occurrence Neurology India 2002; 50: 75-80. 2. Khong PL, Chan GCF, Shek TWH, Tam PKH, Chan FL. Imaging of peripheral PNET: Common and uncommon locations. Clin Radiol 2002; 57: 272-277. 3. Ibarburen C, Haberman JJ, Zerhouni EA. Peripheral primitive neuroectodermal tumors. CT and MRI evaluation. Eur J Radiol 1996; 21: 225-232. 4. Mawrin C, Synowitz HJ, Kirches E, Kutz E, Knut D, Weis S. Primary primitive neuroectodermal tumor of the spinal cord: case report and review of literature. Clin Neurol Neurosurg 2002; 104: 36-40. 5. Kim YW, Jin BH, Kim TS, Cho YE. Primary intraspinal primitive neuroectodermal tumor at conus medul- laris. Yonsei Med J 2004; 45: 538. 6. Dorfmuller G, Wurtz FG, Umschaden HW, Kleinert R, Ambros PF. Intraspinal primitive neuroectodermal tumour: Report of two cases and review of literature. Acta Neurochirur 1999; 141: 1169-1175. 7. Isotalo PA, Agbi C, Davidson B, Girard A, Verma S, Robertson SJ. Primitive neuroectodermal tumor of the cauda equina. Hum Pathol 2000; 31: 999-1001. 8. Dick EA, McHugh K, Kimber C, Michalski A. Imaging of non-central nervous system primitive neuroecto- dermal tumours: Diagnostic features and correlation with outcome. Clin Radiol 2001; 56: 206-215. 9. Meltzer CC, Townsend DW, Kottapally S, Jadali F. FDG imaging of spinal cord primitive neuroectodermal tumor. J Nucl Med 1998; 39: 1207-1209. 20 SA JOURNAL OF RADIOLOGY • March 2006 PRICE: R399.00 To order contact: The South African Medical Association, Health & Medical Publishing Group 1-2 Lonsdale Building, Gardener Way, Pinelands, 7405. Tel: (021) 530-6520/27 Fax: (021) 531-4126/3539 email: carmena@hmpg.co.za or avrilm@hmpg.co.za paraspinal.indd 20 3/27/06 12:25:57 PM