Teaching Case

A female patient presented to surgical outpatient department complaining of intermittent swelling in her right lower quadrant. Her past medical history was unremarkable without previous abdominal surgery. Physical examination revealed local tenderness at palpation without peritonism. Routine laboratory tests were within normal limits.

Unenhanced multidetector CT was requested to investigate possible causes of the patient’s complaints, particularly to rule out acute appendicitis and caecal diverticulitis.
As the only abnormal finding, multiplanar CT images (Fig. 1) showed right-sided herniation of preperitoneal fat, peritoneal serosa and caecum, through a 3-cm defect located between the rectus abdominis and oblique muscles into the subcutaneous planes, consistent with Spigelian hernia. The herniated fat showed normal attenuation. Signs of bowel obstruction and ischaemia, mesenterial oedema and ascites were not present.
The attending surgeon indicated the need for elective repair.

Spigelian hernia (SH) is a rare acquired herniation of the ventrolateral abdominal wall which accounts for less than 2% of all hernias. SH involves the protrusion of extraperitoneal fat and peritoneum - with or without abdominal viscera - through the Spigelian aponeurosis, most commonly between the umbilicus and the anterosuperior iliac spine, along the semilunar line where the aponeurosis is widest. The hernial sac may be empty or contain small bowel loops (in 33-75% of patients); conversely sigmoid colon or caecum herniation is uncommon. SH usually (80% of cases) extend between the internal and external oblique layers (interstitial form), or sometimes cross the external oblique muscle to reach the subcutaneous compartment [1-4].
Usually diagnosed during the sixth decade of life, SH may occur in both sexes, on either side and sometimes bilaterally. Predisposing factors include obesity, chronic obstructive lung disease, multiple pregnancies, rapid weight loss, previous surgery or laparoscopy. Presentation is variable depending on size and hernial sac content, and is sometimes (20% of cases) acute as a tender irreducible mass. Patients often complain of postural or intermittently palpable swelling, local pain and tenderness. Symptoms and physical findings are generally subtle or inconclusive particularly in obese patients, the hernial port is usually narrow and difficult to localize. Because of its narrow neck (approximately 2-3 cm) SH is prone to complications including irreducibility, small bowel obstruction and incarceration, the latter reported in 17-24% of cases. Closed-loop obstruction may lead to bowel strangulation and necrosis, thus representing a surgical emergency [1-5].
Surgical repair is mandatory in most cases because of the high complication risk, sometimes on an emergency basis, and is increasingly performed with a laparoscopic rather than open approach [3, 4].
Therefore, SH represents a challenging but critical preoperative diagnosis. Currently CT is considered the most accurate modality to identify, differentiate and characterize the various types of abdominal wall hernias, particularly clinically occult ones, providing confident diagnosis of anatomic herniation site plus size, shape, and content of the hernial sac, and signs indicating complications. In the majority of cases SH is diagnosed by CT, with 100% sensitivity and positive predictive value. The valuable, detailed CT information allows a direct surgical approach, including hernia anatomy, neck size and content, and categorization as interstitial or subcutaneous. Furthermore, SH may represent a clinically significant incidental finding in CT examination. Conversely, ultrasound has limited sensitivity, particularly in overweight patients [1, 4-6].