Unusual perianal tumours masquerading as abscesses.

Tumours of the perianal region and anal canal are uncommon and can present in a variety of ways. Acute anorectal sepsis is a common condition that usually presents as a painful lump close to the anal margin. Tumours in the perianal region may mimic the symptoms and signs of anorectal sepsis, thereby leading to a delay in diagnosis and management. We report three patients who presented to our department with symptoms and signs suggestive of perianal abscess but which on further investigation were discovered to be due to unusual perianal tumours. Only one of the tumours was found to be malignant--a primary perianal mucinous adenocarcinoma; the other two were benign, a leiomyoma and an aggressive angiomyxoma. A high index of clinical suspicion is required to the diagnosis of perianal tumours when assessing patients with painful perianal lumps, particularly those with a long history and those of ethnic origin. Every effort should be made to establish a preoperative diagnosis so that correct treatment can be delivered.

Registration of MR and CT images for skull base surgery using point-like anatomical features.

We have developed a registration technique for combining magnetic resonance imaging (MRI) and computed tomography (CT) images of the skull base for use in surgical planning. The technique is based on user identification of point-like landmarks visible in both modalities. The combination of images involves a small amount of expert interaction, is relatively quick and preliminary evaluation indicates that it is accurate to within 1.5 mm. Registered or fused images can be viewed either on an image processing workstation, or fused images can be printed onto conventional film for convenience in clinical use. We present one patient in order to demonstrate the technique's indications and advantages.