Introduction Primitive neuroectodermal tumors PNETs) are malig- nant tumors that belong to the group of small round blue-cell tumors of childhood, which includes Ewing's sarcoma, rhabdomyosarcoma, small-cell osteosarcoma, neuroblastoma, and hematolymphoid neoplasms [1]. The most common sites of involvement of PNETs are the chest wall, abdomen/pelvis, and extremities [2]. Males are more commonly affected than females [1] and typically present during the second decade of life [2]. We report a case of a PNET arising from the dia- phragm of a neonate. Case report A male infant weighing 3,250 g was born at 37 weeks' gestation. The baby demonstrated hypotonia and respiratory distress min- utes after birth. Further deterioration led to intubation, and the first chest X-ray Fig.1a) showed a presumed large right pleural effusion with shift of the heart and mediastinum to the left. A chest tube was inserted that drained 40±50 cc of straw-colored flu- id. Cytology demonstrated mesothelial cells, monocytes, and red blood cells, but was negative for malignant cells. A repeat chest X-ray at 5 days of age demonstrated slight recurrence of the pleu- ral effusion, and a pleurocentesis was performed. The infant was at that time asymptomatic and was subsequently discharged the following day with the diagnosis of idiopathic right pleural effu- sion. Two days after discharge the infant again developedrespiratory distress secondary to a large recurrent right pleural effusion, and thoracentesis produced 100 cc of serous/yellow fluid, which was sent for cytology. The pleural fluid rapidly reaccumulated, requir- ing two more chest tube insertions. A PA chest X-ray Fig.1b) done at 17 days of age demonstrated moderate-sized right pleural effusion and a possible mass in the costophrenic sulcus. An ultra- sound performed at this time demonstrated diminished excursion of the right hemidiaphragm. A solid mass with some cystic compo- nents measuring 4.5  3.5 cm was seen in the posterior sulcus, ap- pearing to be attached to the diaphragm by a pedicle Fig.2). No blood flow was seen in the mass. At this time the differential diag- nosis included extralobar sequestration, neuroblastoma, mesen- Marie S. Smerdely Gregory Raymond Kendra L. Fisher Ravi Bhargava Primitive neuroectodermal tumor of the diaphragm: case report Received: 10 March 2000 Accepted: 11 May 2000 M.S.Smerdely ´ G.Raymond ´ R.Bhargava  ) ) University of Alberta, Department of Radiology and Diagnostic Imaging, 2A2.42 Walter C Mackenzie Health Sciences Center, University of Alberta Hospital, Edmonton, Alberta, T6G 2B7, Canada Tel.:+1-780-4076907 Fax:+1-780-4076176) K.L Fisher Department of Radiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada Abstract We present a case of primitive neuroectodermal tumor PNET) arising from the diaphragm in a neonate. PNETs are rare malig- nant tumors that belong to the group of small, round, blue-cell neoplasms of childhood. To the best of our knowledge, a PNET originat- ing from the diaphragm has not been previously reported. Pediatr Radiol 2000) 30: 702±704 Ó Springer-Verlag2000