Introduction Ruptured neonatal intracranial arterial aneurysms are ex- tremely rare. Only 13 such cases have previously been re- ported in the literature, all but 1 of which were of the sac- cular type. Fusiform aneurysms may occur in dysplastic vascular segments. Case report An 11-day-old male infant presented with a 2-day history of irrita- bility, drowsiness, vomiting and reduced urine output. On examina- tion, he was hypertonic with bulging anterior fontanelle, opisthoto- nus and brisk reflexes. A lumbar puncture revealed blood-stained CSF. Within 30 min he started gasping and displayed vertical nys- tagmus, poorly responsive pupils and reducing capillary return with central cyanosis. He required intubation and intermittent positive pressure ventilation. The infant was born at term with meconium- stained liquor. His mother had reported mild antepartum haemor- rhage and reduced fetal movements at 33 weeks of pregnancy. His weight and head circumference at birth were 3.32 kg and 35 cm (36.5 cm on admission), respectively. He had two healthy siblings. Cranial sonography followed by CT showed moderate hydroceph- alus due to extensive subarachnoid and intraventricular haemorrhage, with a predominance of blood in the anterior interhemispheric fissure (Fig. 1). Within this, a rounded hypodense (relative to the haemor- rhage) lesion was evident, highly suggestive of an aneurysm. This was confirmed by magnetic resonance imaging (MR) and digital subtrac- tion angiography (DSA). The maximum intensity projection (MIP) of the 3D time-of-flight MR angiogram (Fig. 2) and DSA (Fig. 3) re- vealed a fusiform aneurysm 10 mm in diameter supplied by the A1 segment of the left anterior cerebral artery. The right A1 segment was completely aplastic, and both A2 segments arose from the anterior por- tion of the aneurysmal sac. There was moderately severe spasm of the left supraclinoid carotid artery and the anterior and middle cerebral ar- teries. Both carotid territories were anatomically otherwise normal. Child’s Nerv Syst (1998) 14:467–469 © Springer-Verlag 1998 CASE REPORT Ruptured fusiform cerebral aneurysm in a neonate M. P. Tan N. S. McConachie M. Vloeberghs Abstract An 11-day-old male in- fant presented with subarachnoid and intraventricular haemorrhage caused by a ruptured intracranial aneurysm. Magnetic resonance (MR) angiogram and digital subtrac- tion angiography (DSA) revealed a fusiform aneurysm 10 mm in diame- ter supplied by the proximal segment of the anterior cerebral artery (A1), with both distal segments (A2) arising from the aneurysm. The right A1 was aplastic. There have been 13 previous case reports of neonatal cerebral artery aneurysms, but only 1 of these has been fusi- form. None of the earlier reports has mentioned dysplastic segments or other anomalies of the circle of Willis. Key words Cerebral aneurysm · Neonate · Intracranial haemorrhage · Circle of Willis Received: 17 November 1997 M. P. Tan · M. Vloeberghs () Department of Paediatric Neurosurgery, Queen’s Medical Centre, Nottingham NG7 2UH, UK Tel.: +44-115-924 9924, ext. 43635 Fax: +44-115-970 9103 N. S. McConachie Department of Neuroradiology, Queen’s Medical Centre, Nottingham NG7 2UH, UK Fig. 1 CT scan shows extensive subarachnoid and intraventricular haemorrhage with a localised haematoma in the anterior interhemi- spheric fissure. The aneurysm is represented by an area of relative hypodensity within the haematoma