Iliohypogastric Nerve Entrapment
M El-Muhtaseb, G MacKay, I MacKenzie
A 44 year-old woman underwent an open appendectomy for suspected acute appendicitis carried out through a gridiron muscle spreading incision (as shown in figure 1).
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On the second post-operative day the patient began to complain of persistent pain in the region of the superficial inguinal ring on the right side. Examination revealed tenderness at the superficial inguinal ring with no alteration in sensation. Examination of the wound was otherwise unremarkable.
The initial impression was one of iliohypogastric nerve entrapment. A trial of infiltration of local anaesthetic was carried out with o.25% Bupivicaine at a point 2cm medial to the anterior superior iliac spine deep to the external oblique muscle. Following infiltration of the local anesthetic the pain resolved after a period of 20 minutes only to return after 3 hours, which is consistent with the onset and duration of action of Bupivicaine.
As her symptoms persisted unchanged over the following 7 days, the decision was taken to explore the wound. Exploration was carried out through the original wound and the iliohypogastric nerve was found to be caught in the suture used to approximate the internal oblique muscle fibers (as shown in figure 2). The suture was released and the wound was closed in standard fashion.
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Following this procedure the patient failed to experience relief of her symptoms. Furthermore a trial of amitriptyline was also unsuccessful. Further re-exploration was carried out and both the iliohypogastric and ilioinguinal nerves were divided. Following this procedure the patient's symptoms resolved and she was discharged from hospital.
Discussion
The Iliohypogastric nerve is in danger during open appendectomy procedure either during the opening or closing of the abdominal wall layers especially if the wound extends laterally to less than 3cm from the anterior superior iliac spine . The patient usually presents early in the postoperative period but can occasionally present later, some months after the operation.
The diagnosis is clinical. There may be evidence of impaired sensory perception along the distribution of the iliohypogastric nerve and the diagnosis is confirmed by a positive anaesthetic test (iliohypogastric nerve block ).
If the diagnosis has been confirmed and the symptoms produce significant discomfort, treatment options are analgesia, nerve block, local steroid injection and neurolysis. Neurolysis is not recommended due to recurrence of the symptoms as a result of progressive fibrosis. The most effective treatment is neurectomy, which is usually well tolerated by the patient. In this case we suspect that continuing neuropraxia was the explanation of persisting pain after the nerve was released from the encircling suture.
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