A 19-year-old male patient referred from a regional hospital for surgery for hydrocephalus. He had a history of approximately 1 year of left hemicranial headache that worsened on exertion. In recent weeks the headache had increased in intensity and frequency. The neurological examination showed only bilateral papillary oedema.

The patient provided a magnetic resonance imaging (MRI) scan showing supratentorial ventricular dilatation with an Evans index of 0.43, periependymal clearing in the frontal horn and a small tectal lesion that was not modified by contrast. The fourth ventricle was normal.

With the diagnosis of stenosis of the aqueduct of Sylvius, an endoscopic premamillary ventriculocysternostomy was performed through a right frontal trephine hole according to the standard technique3. A Mayfield clamp (Ohio Medical Instrument Co, Inc., Cincinnati, Oh, USA) was used for head immobilisation. The immediate postoperative period was uneventful, although the patient suffered from headache. Forty-eight hours after surgery and prior to the scheduled discharge from hospital, a new MRI was performed in which the presence of a left parietal epidural haematoma with a mass effect on the ipsilateral lateral ventricle was noted.

A left parietal craniotomy was then performed, showing a perforation that went through the entire bone without affecting the dura mater. The haematoma was drained and a small bleeding dural artery was coagulated. The patient was discharged after 6 days with only some degree of headache. One year after surgery he is asymptomatic and the tectal lesion shows no change on MRI studies.