Most Spigelian hernias occur below the level of the umbilicus close to the level of the arcuate line. We report a case diagnosed by computed tomography in an unusually high anatomical location due to a previous drain site incision.

The hernial orifice of a Spigelian hernia is usually located along the semilunar line (Spigelian line) through the transversus abdominis aponeurosis (Spigelian fascia) close to the level of the arcuate line. The majority of Spigelian hernias are found in a transverse band lying 0-6 cm cranial to a line running between both anterior superior iliac spines referred to as the Spigelian hernia belt.¹ Though Spigelian hernias have been documented to occur above the level of the umbilicus^1,2 we report a case in which the hernial orifice was 12 cm above the level of the arcuate line in an unusually high anatomical location. A possible predisposing factor for the hernia in this case was a previous drain site incision at this site many years previously.

A 68-year-old man presented in March 1998 with sudden onset of right sided abdominal pain of four hours duration. This was not associated with nausea or vomiting. Past medical history included ischaemic heart disease, atrial fibrillation, and recent pulmonary embolism for which he was commenced on warfarin. The patient had undergone several surgical procedures in the past for the treatment of a gastric ulcer which included vagotomy and gastrojejunostomy, pyloroplasty and a Bilroth I partial gastrectomy. The patient failed to remember precisely when these surgical operations were performed but estimated it was about 28 years ago. On examination his vital signs were stable. There was an approximately 10 cm large ill-defined firm palpable mass over his right upper abdomen. On close examination a one inch scar was present on the medial aspect of his swelling, which was thought to be due to a previous drain site incision. Bowel sounds were audible. Needle aspiration of the mass revealed blood stained fluid. A provisional clinical diagnosis of external abdominal wall haematoma was made. However, his condition deteriorated the following day and the mass became increasingly tender.

A computerised tomography (CT) scan of the abdomen with oral and intravenous enhancement (Figure 1) was then performed for further evaluation of the anterior abdominal mass. This showed a large hernia in the right upper abdominal wall with interposed omental fat and a loop of small bowel between the internal oblique and transversus abdominis muscles. The hernia had a narrow neck along the semilunar line approximately 12 cm superior to the level of the arcuate line. The small bowel proximal to the hernia was dilated, although a small amount of contrast medium was seen to pass into the undilated small bowel distal to the hernial orifice. A diagnosis of an incarcerated Spigelian hernia, causing incomplete small bowel obstruction, was made.

The CT scan findings were confirmed at laparotomy. A necrotic segment of ileum measuring 14 cm in length and omental fat was resected from the hernial sac lying between the internal oblique and transversus abdominis muscles. The neck of the hernia was a narrow defect in the transversus abdominis muscle, which was repaired with interrupted number one polypropylene (Prolene). The patient made an uneventful recovery and was discharged on the seventh post-operative day.

The arcuate line marks an anatomic transition point below which all the aponeurotic layers of the abdominal muscles, except the transversalis fascia, pass anterior to the rectus abdominis. The arcuate line may be represented by a transverse line connecting both anterior superior iliac spines.³ The hernial orifices of most Spigelian hernias occur at, or close to, the arcuate line, as the anterior abdominal wall here is only weakly reinforced by slightly separated fascial bands. Moreover, the Spigelian fascia is present in significant width only below the level of the umbilicus. Although Spigelian hernias have been reported to occur above the level of the umbilicus^1,2 it is rare for them to do so. A further reason is that above the umbilicus the fibres of the transversus abdominis and internal oblique muscles cross one another at angles, making herniation more unlikely than if the fibres were to run parallel, as they do below the umbilicus. The literature^1,2,3-6 does not document the highest level at which Spigelian hernias have been known to occur, but this case clearly demonstrates that such a hernia can occur well above the conventional Spigelian hernia belt if there is a predisposing factor such as a previous drain site incision, as in this case. Herniation through a drain site is a rare but recognised complication of surgical drainage.^7,8 This case also highlights the value of CT scanning in making an accurate pre-operative diagnosis of Spigelian hernia when the anatomical site of presentation is atypical.

Correspondence: J.M. Rehman, Consultant Radiologist, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK

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A case of a Spigelian hernia at an unusually high anatomical location

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