What is a Spigelian Hernia?
A Spigelian hernia is a rare type of ventral abdominal wall hernia that occurs through a defect in the Spigelian aponeurosis—the aponeurotic layer of the transverse abdominal muscle located between the lateral edge of the rectus abdominis muscle medially and the linea semilunaris (semilunar line) laterally. 1
Anatomical Definition and Location
The Spigelian hernia represents protrusion of preperitoneal fat, peritoneal sac, or abdominal organs through a congenital or acquired defect in the Spigelian fascia 1
Most Spigelian hernias (approximately 90%) occur in the "Spigelian hernia belt"—a transverse 6-cm-wide zone located above the interspinal plane in the lower abdomen 1
The hernia is also known as a spontaneous lateral ventral hernia or interparietal hernia 2, 3
Lower hernias below this belt are rare and must be differentiated from direct inguinal or supravesical hernias 1
Epidemiology and Clinical Significance
Spigelian hernias account for only 1-2% of all abdominal wall hernias, making them quite uncommon 1
Approximately 1,000 cases have been reported worldwide as of 2010 3
The left side is the most frequently affected location 4
These hernias carry a high risk of incarceration and strangulation because they are often interparietal (occurring between muscle layers) and may not present with an obvious subcutaneous swelling 3
Etiology
Defects in the aponeurosis of the transverse abdominal muscle, particularly below the arcuate line and more commonly in obese individuals, are considered the principal etiologic factor 1
In pediatric cases, especially neonates and infants, Spigelian hernias are mostly congenital 1
Embryologically, these hernias may represent weak areas in the continuation of aponeuroses of layered abdominal muscles as they develop separately in the mesenchyme during fetal development 1
Risk factors are present in approximately 74% of patients who develop Spigelian hernias 4
Clinical Presentation and Diagnostic Challenges
Diagnosis is difficult because Spigelian hernias often do not present with a visible subcutaneous swelling, as the hernia may be covered by the external oblique muscle 3
Patients typically present with point tenderness and pain in the lower abdominal wall, with symptoms that may decrease when lying down 3, 5
A hernia bulge is best detected by palpation of the abdominal wall with the patient coughing or straining while standing 5
Clinical examination alone establishes the diagnosis in approximately 72% of cases 4
CT scan is the gold standard imaging modality in doubtful cases 4
An important percentage of patients (approximately 20%) will present with acute complications such as incarceration or strangulation as their first symptom, requiring emergency operation 4