113 Ilioinguinal/Iliohypogastric Neuropathy R. Graham Vanderlinden, Rajiv Midha, and Loren Vanderlinden

Introduction

Persistent pain following inguinal hernia repairs is a significant problem. Marsden1 reported a series of 939 inguinal hernia re­pairs in which 2.8% of patients still suffered significant wound pain at 1 year and 1.4% were substantially disabled at 3 years. Entrap­ment of the ilioinguinal or the iliohypogastric nerves may be caused by suture placement, tendinous bands, fibrous adhesions, or neuroma formation.

Lumbar plexus lesions were recorded by Osler2 in 1910, but the syndromes of genitofemoral and ilioinguinal/iliohypogastric neu­ralgia were first reported by Magee3 and Lyon4 as being surgically correctable. These authors and others5-l0 have noted that the il­ioinguinal/iliohypogastric nerves can be entrapped following ap­pendectomies, blunt trauma, or urological operations as well as inguinal herniorrhaphies. Purves and Miller7 believe strongly that injury to the genitofemoral nerve occurs at the time of pelvic surgery.

Anatomy

The cutaneous branches of the lumbar plexus give rise to the il­iohypogastric, ilioinguinal, and genitofemoral nerves, the lateral femoral cutaneous nerve of the thigh, and the obturator nerves.

The iliohypogastric is a motor and sensory nerve arising from the Tll, T12, and Ll nerve roots. It emerges from behind the lat­eral edge of the psoas muscle and pierces the transversus abdo­minis muscle above the iliac crest. Its anterior branch runs forward between the internal oblique muscle and the external oblique aponeurosis, which it penetrates to supply the skin above the pu­bis. Its posterior branch supplies an area of the buttock just pos­terior to the iliac crest.

The ilioinguinal nerve is also a mixed nerve arising primarily from Ll but also receiving branches from T12 that emerges be­hind the psoas muscle below the iliohypogastric nerve. It passes obliquely across the quadratus lumborum and iliac muscles and perforates the transverse abdominal and internal oblique muscles medial to the anterior superior iliac crest. It runs along the in­guinal canal and emerges through the external ring. It provides sensation to the upper medial aspect of the thigh and the base of the scrotum and labia. Mossman and Oelrichll studied 424 in-

guinal areas and found a "normal" course in only 60%. In 35% the ilioinguinal nerve appeared as a branch of the iliohypogastric or genitofemoral nerves.

The genitofemoral nerve arises from Ll and L2 and consists mainly of sensory fibers with a motor branch to the cremasteric muscle (efferent component of the cremasteric reflex). It travels obliquely through and over the psoas muscle, emerging in the retroperitoneal space opposite the L4 vertebral body. It divides into the genital (external spermatic) and femoral (lumboinguinal) branches, which travel separately behind the ureter and across the base of the broad ligament. The genital branch crosses the lower end of the external iliac artery and enters the inguinal canal through the internal ring. It follows the spermatic cord or round ligament and supplies sensation to the scrotum or labia and me­dial upper thigh. The femoral branches descend lateral to the ex­ternal iliac artery behind the inguinal ligament; passing through the fascia lata, they enter the femoral sheath where they lie literal to'the femoral artery. These branches supply sensation to the up­per anterior thigh.

Diagnosis

Ilioinguinal and iliohypogastric neuralgia and entrapment may oc­cur spontaneously, as a result of congenital bands, or as a )ZOm­

plication from operations on the lower abdominal wall and inguinal region (Table 113.1). The ilioinguinal clinical triad is

l. Pain-sharp, stabbing, or aching and burning, in the groin with radiation to the pubic tubercle and proximal inner thigh

2. Sensory abnormalities-hypoesthesia, hyperalgesia, or allody­nia in the ilioinguinal dermatome

3. A circumscribed trigger point medial to and below the anterior superior iliac spine, where pressure reproduces the character­istic pain radiation

Iliohypogastric pain is distributed above the pubis, and the point of maximum tenderness is often above the midpoint of the in­guinal ligament. Genitofemoral pain is more medial than ilioin­guinal pain, and the point of maximum tenderness is at the pubic tubercle or external inguinal ring. Distinguishing genitofemoral neuralgia from ilioinguinal neuralgia can be difficult and at times impossible.

737 R. Bendavid et al. (eds.), Abdominal Wall Hernias© Springer Science+Business Media New York 2001

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TABLE 113.1. Etiology of ilioinguinal/iliohypogastric neuralgia

1. Inguinal hernias or postherniorrhaphy 2. Previous abdominal surgery

a. Appendectomy (McBurney) b. Gynecological (Pfannenstiel) c. Retroperitoneal

3. Congenital tendinous bands

Local blocks of the ilioinguinal/iliohypogastric nerves with bupivacaine at the trigger point medial to the anterior superior il­iac spine and of the genital nerve at the external ring can usu~lly differentiate between these two neuralgias and confirm the diag­nosis. The addition of steroids did not produce prolongation of pain relief. Differential paravertebral blocks of the TIl, T12, Ll, and L2 nerve roots were also used in some patients.

There is no "typical" case history, although the following is il­lustrative of some of the difficulties experienced by both patient and physician in dealing with this entity. A 31-year-old woman de­veloped intermittent right lower quadrant pain following a mis­carriage in 1983. In 1986, a right inguinal hernia was repaired and the symptoms subsided. The hernia recurred 5 months later fol­lowing childbirth. The hernia was re-repaired in 1987, and the il­ioinguinal nerve was explored and scar tissue removed. Her pain was not relieved but progressed in severity and radiated to the an­teromedial thigh and sometimes to the posterior superior iliac spine. There was constant discomfort, but, at times, the pain was sharp and she graded it as 8 out of 10 on the visual analogue scale. The severe pain was precipitated by coitus, and she was unable to lie supine without flexing her hips.

Assessment by three gynecologists, two laparoscopic examina­tions, abdominal ultrasound, barium enema, and colonoscopy showed no abnormalities. Examination demonstrated focal ten­derness medial to the anterior superior iliac spine and at the external inguinal ring, mild hyperalgesia in the ilioinguinal der­matome, and restriction of back extension and left lateral bend­ing due to right lower quadrant pain. Two ilioinguinal nerve blocks relieved the pain.

In 1992, an attack of periumbilical pain resulted in laparoscopic removal of a fibrotic, noninflamed appendix. There was no change in her pain following this surgery. In 1993 the inguinal region was explored, and the ilioinguinal nerve was found to be invested in dense scar tissue necessitating removal of a 5 cm length of the nerve.

The patient did well for 6 months, but the pain recurred and began to interfere seriously with her life. Paravertebral blocks of the TIl, T12, and Ll nerve roots relieved her pain and, in June 1994, microsurgical dorsal root ganglionectomies were done. The patient resumed her normal activities and remained pain free 5 years later.

Surgical Treatment of Ilioinguinal Neuropathy

Decompression or Neurolysis (38 Patients)

The inguinal area was explored by means of an incision beginning superior and medial to the anterior superior iliac spine, extend­ing parallel to the inguinal ligament and ending at the pubic tu-

R.G. Vanderlinden et al.

bercle. The external oblique aponeurosis was opened parallel to its fibers down to the external inguinal ring. The ilioinguinal and iliohypogastric nerves were identified and dissected along their courses from the internal oblique to the external ring and rectus sheath, respectively. There was considerable anatomical variability in the course of these nerves. If the nerve was obviously entrapped by tendinous bands at the point of exit from the internal oblique muscle, a decompression or neurolysis was done.

Successful pain relief was achieved in 34% of patients, while 50% of cases were failures and 16% were lost to follow-up. Three of these patients required repair of an unsuspected direct hernia at the time of surgery.

Neurectomy (29 Patients)

Neurectomy was done in patients who had failed decompression or where previous surgery had invested the nerve in extensive scar­ring. Successful pain relief was obtained in 60% of patients, fail­ures were observed in 38%, and one patient was lost to follow-up.

Dorsal Root Ganglionectomy (14 Patients)

This procedure was offered to patients who failed the above pro­cedures and demonstrated good relief of pain from paravertebral blocks. The microsurgical resection of the sensory components of TIl, T12, and Ll nerve roots was done through a paraspinal muscle-splitting incision about 1 cm lateral to the lateral portion of the intervertebral foramina. Permanent anesthesia in the groin area was produced, but in four patients it was subsequently nec­essary to extend the ganglionectomies up to T9 and T10 or down to L2. The success rate was 50%, while failure to produce pain re­lief was observed in 30%. Twenty percent of patients were lost to follow-up (Table 113.2).

Discussion

Injury to peripheral nerves often produces a neuritic pain syn­drome.l2 This, at times, can be further complicated by autonomic dysfunction, and in some cases, by sympathetically mediated pain (autonomic dysreflexia). Although these severe and difficult to manage pain syndromes usually follow damage to major limb or plexus nerve elements, injury to cutaneous peripheral nerves may also produce similar severe neurogenic pain syndromes. Moreover, injured cutaneous nerves have a propensity to regenerate and of­ten form painful neuromas.

The iliohypogastric, ilioinguinal, and genitofemoral nerves are all at risk for iatrogenic injury in lower abdominal wall, inguinal, and groin operations. I~ury to these nerves is best avoided by

TABLE 113.2. Overall results of surgical treatment (follow-up for 1 to 28 years)

Percent No. of patients

Successful 60 37 Failed 24 15 Lost to follow-up 16 10 Total 100 62

113. Ilioinguinal/Iliohypogastric Neuropathy

careful exposure and protection during the procedure. If acci­dental damage occurs, intraoperative management should be di­rected toward avoidance of painful neuroma development. Because an injured nerve has tremendous potential for attempted regeneration, two general forms of surgical treatment are indi­cated. Either the nerve should be immediately repaired, directing axons toward the end-organ, or the proximal stump of the nerve should be placed in an environment where a neuroma will not form or will be clinically innocuous. First, a wide excision of the proximal nerve is performed. Some authors consider coagulation of the nerve stump.13 The proximal stump is then buried or allowed to retract deep to muscular tissue,14 far from the skin in­cision and superficial tissue. In the case of iliohypogastric, ilioin­guinal, and genitofemoral nerves, proximal excision to the level where the nerves can retract into a retroperitoneal location would suffice. Although not advocated by us, some inguinal hernia sur­geons intentionally divide these nerves. I5 In these circumstances, we would recommend a wide excision of the nerve to allow re­traction of the proximal stump into a retroperitoneal site.

Ongoing pain or a new onset of pain (especially neuralgic) fol­lowing inguinal hernia surgery should alert the clinician to the possibility of injury or persisting entrapment of the ilioinguinal and/ or iliohypogastric nerves. A careful history and clinical ex­amination, aided by appropriate nerve blocks, often allows the di­agnosis to be made.

The majority of these patients have a painful neuropathic con­dition. Sensory loss is not clinically important; in this circumstance the goal is to eliminate the patient's pain problem. The initial ap­proach may be conservative, using one or a combination of phys­ical modalities, psychotherapy and pharmacotherapy. Many of these patients have already visited a pain clinic and been treated with various medications. If not, a course of tricyclic agents is worthwhile, such as amitriptyline (Elavil®). An alternative to amitriptyline is the newer generation of serotonin selective in­hibitors, such as sertraline (Zoloft®). Other medications that are occasionally beneficial include anticonvulsant agents such as car­bamazepine (Tegretol®), phenytoin (Dilantin®), and gabapentin (Neurontin®), as well as newer generation nonsteroidal antiin­flammatory drugs such as ketorolac (Toradol®). Narcotic medica­tions should be avoided and discouraged in these situations.

For those patients with an obvious painful neuroma, and oth­ers with a painful nerve injury not responding to conservative treatment, especially where a nerve block has been successful in ameliorating pain, a peripheral nerve surgical procedure is war­ranted. Intraoperative management is dictated by the generally ac­cepted principles of neuroma surgery.13 There are three general procedures available for painful cutaneous nerve injury condi­tions: neurolysis, nerve repair (primary suture or grafting), and neurectomy.

Neurolysis carries the benefit of preservation of sensory func­tion (if, in fact, this is retained postinjury). Neurolysis appears to

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achieve reasonable results where the nerve is primarily entrapped and not injured, as demonstrated in about one-third of the pa­tients in this series. However, the results of neurolysis appear to be poor for long-term pain control in over half the patients. This is similar to the generally poor results of neurolysis for cutaneous nerve injuries that result in painful neuromas. I3 In circumstances of excessive nerve scarring and painful neuroma, a neurolysis pro­cedure is probably doomed to failure.

Nerve repair and grafting has some theoretical merit in that re­generating axons can be directed away from the zone of nerve in­jury and scar.14 However, patients have been reported who develop a neuroma within the suture line, resulting in an equally in­tractable recurrence of pain.I3 Also, grafting requires harvesting of a donor nerve, and this has obvious drawbacks. The most reli­able procedure remains a neurectomy. The patient must accept the trade-off: loss of sensory function for probable relief of pain. Because the ilioinguinal and iliohypogastric nerves do not supply sensation to a critical area, the sensory deficit is well tolerated.

References

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11. Moosman DA, Oelrich RM. Prevention of accidental trauma to the il­ioinguinal nerve during inguinal herniorrhaphy. Am] Surg. 1977;133: 146-148.

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13. Kline DG, Hudson AR Nerve injuries: operative TliSUlts from major nerve injuries, entrapments, and tumors. Philadelphia: W.B. Saunders; 1995.

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