Gangliform Enlargement on the Lateral Cutaneous Nerve of the Thigh

Its Significance in the Understanding of the Etiology of Meralgia Paresthetica

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Gangliform enlargements (“pseudoganglions”) have been described3,6,9,10,21 at or near the termination of various nerves of the body such as the median nerve, the anterior tibial (deep peroneal) nerve, the nerve to the teres minor muscle, and the posterior interosseous nerve. In the present study a similar enlargement will be described as found frequently on the lateral cutaneous nerve of the thigh. Its existence is not mentioned in current textbooks or other anatomical literature and its presence may throw some light on the etiology of meralgia paresthetica.

MATERIAL

The present work is based

Gangliform enlargements (“pseudoganglions”) have been described3,6,9,10,21 at or near the termination of various nerves of the body such as the median nerve, the anterior tibial (deep peroneal) nerve, the nerve to the teres minor muscle, and the posterior interosseous nerve. In the present study a similar enlargement will be described as found frequently on the lateral cutaneous nerve of the thigh. Its existence is not mentioned in current textbooks or other anatomical literature and its presence may throw some light on the etiology of meralgia paresthetica.

MATERIAL

The present work is based on 60 dissections of the lateral cutaneous nerve of the thigh in cadavers.

DESCRIPTION

In 10 (17 per cent) of the specimens, a fusiform swelling of the lateral cutaneous nerve of the thigh was found (Fig. 1).

Fig. 1.
Fig. 1.

Gangliform enlargement of lateral cutaneous nerve of the thigh. The enlargement is spindleshaped, and localized in that part of the nerve passing from the pelvis to the thigh, just in front of the anterosuperior iliac spine. The nerve and swelling have been slightly raised by means of forceps.

l.c.n.—lateral cutaneous nerve of thigh; g.e.—gangliform enlargement; i.m.—iliacus muscle; p.m.— psoas major muscle; p.m.m.—psoas minor muscle; s.m.—sartorius; s.i.a.—anterosuperior iliac spine; c.i.—iliac crest; e.o.m.—aponeurosis of external oblique muscle, reflected downwards.

In 26 (43 per cent) a progressive, nonfusiform, broadening of the terminal part of the nerve was observed (Fig. 2).

Fig. 2.
Fig. 2.

Progressive, nonfusiform enlargement of lateral cutaneous nerve of thigh. The enlargement starts proximal to the inguinal ligament and continues to expand distal to the ligament to the point where the nerve divides into its terminal branches.

i.l.—portion of inguinal ligament; its cut ends are grasped by forceps, f.n.—femoral nerve.

For remaining abbreviations see legend to Fig. 1.

In the remaining 24 cases (40 per cent) there was no substantial change in width of the nerve along the whole length of its course.

When the gangliform enlargement was spindle-shaped (Fig. 1), it was generally localized in the part of the nerve passing beneath the inguinal ligament (Poupart's ligament); at that point the nerve describes a more or less acute angle open downwards and posteriorly (Fig. 3). This angulation comes about as consequence of a change in the direction of the nerve when passing from the pelvis to the thigh. In the beginning of its course, after appearing from under the lateral border of the psoas muscle, the nerve runs laterally downwards, and forwards, included in the iliac fascia;23 before reaching the inguinal ligament, it becomes more horizontal or even ascends slightly. When crossing the inguinal ligament, the nerve sharply changes its direction to run downwards and, sometimes, slightly posteriorly. Starting slightly proximal to the inguinal ligament and ending somewhat distal to it, the swelling occupied the apex of the angle; and it lay on the iliac muscle, on the proximal part of the sartorious and on a fibrous tissue between these two muscles. The inguinal ligament does not appear to compress the nerve at this point. It varied in length between 15 and 30 mm.; in breadth it varied between 3 and 8 mm., while the original width of the same nerve, as it emerged from the lateral border of the psoas muscle (Figs. 1 and 2), was only 0.5 to 2 mm. In 2 cases the nerves did not pass under the inguinal ligament but crossed over the iliac crest, perforating the abdominal wall, slightly posterior to the anterior iliac spine; in both these cases angulation of the nerve was very sharp and its fusiform swelling was very evident.

Fig. 3.
Fig. 3.

Diagram showing course of lateral cutaneous nerve of the thigh; lateral view. The nerve appears sharply angulated when passing from pelvis to thigh beneath the inguinal ligament; a spindle-shape enlargement is located at apex of the angulation.

The shaded lighter part of the nerve—l.c.n. (a)—shows intrapelvic course of the nerve proximal to inguinal ligament. The darker part— l.c.n.(b)—shows course of the nerve distal to inguinal ligament.

For remaining abbreviations see Fig. 1.

When the enlargement was progressive and nonfusiform (Fig. 2), it also tended to start proximal to the inguinal ligament, but instead of becoming spindle-shaped, it continued to expand and reached its maximal breadth at the point where the nerve divided into its terminal branches, usually not more than a few centimeters distal to the inguinal ligament. In this part of its course the nerve lies within a splitting of the fascia lata,23 as it passes over the origin of the sartorius muscle (Figs. 2 and 3). The enlargement of the nerve at its broadest part varied between 4 and 8 mm.

Anastomotic branches coming from adjacent nerves, generally from the femoral, frequently were found joining the lateral cutaneous nerve in the vicinity of the inguinal ligament. Any enlargement resulting from such an anastomosis was not considered as a swelling of the type described above.

DISCUSSION

There seems little doubt that the gangliform enlargements of the lateral cutaneous nerve of the thigh are of the same nature as similar enlargements observed on other nerves such as the median, posterior interosseous, anterior tibial, and nerve to the teres minor; these appear to develop as a consequence of mechanical friction against the ligaments, tendons or bones, with which they come into close contact.

Daniell6 has studied particularly the enlargements on the anterior tibial (deep peroneal) and medial plantar nerves. He found that the position of the swelling on the lateral branch of the anterior tibial nerve was consistently related to the lateral edge of the dorsal surface of the navicular bone, while the swelling on the medial branch of the nerve was related to the distal edge of the dorsal surface of the navicular bone. Histological sections of these enlargements revealed a greater density of the extrafunicular fibrotic tissue, thickening of the perineurium and an increase of the fibrous elements within the funiculi, their proportions varying in different specimens. In some specimens peculiar hyalinized fibrous structures were also found in the funiculi. In Daniell's6 opinion, the cause of the fibrous reaction and resulting enlargement was a chronic irritation of the nerves.

Sunderland and Bradley27 previously had investigated the relationship existing between the nerve bundles and their perineurial sheaths in different parts of various nerves in the body. They found that the perineurial sheath was thickened in the swelling on the median nerve at the wrist. They observed, moreover, a slight relative increase of perineurium in the ulnar nerve, behind the medial epicondyle of the humerus. They believed that this relative increase of perineurium may be concerned with the protection of the contents of the bundle.

More recently, Gitlin9 studied the swelling on the nerve to the teres minor muscle. He found an intimate relationship between the pseudoganglion and the tendon of the long head of the triceps, and considered that friction during movement may be responsible for the presence of the swelling. He also found that the amount of connective tissue in the enlarged portion was considerably greater than that in the part of the nerve proximal to the enlargement, the increase affecting epineurium, perineurium and endoneurium.

With regard to the lateral cutaneous nerve of the thigh, the cause of irritation and subsequent enlargement would appear to be the friction engendered by the movements of the lower limb at the point where the nerve passes from the pelvis to the thigh either beneath the inguinal ligament or over the iliac crest. As observed, the nerve is markedly angulated at this part of its course (Fig. 3,) and it has been noted26 that it is sometimes submitted to a considerable degree of tension, particularly during extension of the thigh, or in the erect posture. It is possible that this same friction and irritation of the nerve are an etiological factor in the syndrome known as meralgia paresthetica. The clinical condition, first described in 1895 independently by Roth25 and by Bernhardt2 is characterized by paresthesia, pain, anesthesia and sometimes a tendency for the hair to fall out, along the lateral surface of the thigh over the area of distribution of the lateral cutaneous nerve. Unilateral or bilateral, the symptoms generally are more marked on walking or standing. Its etiology is not always clear, and it has been attributed to many different causes.19

From a general review of the literature on the subject17 it would appear that from the etiological point of view cases of meralgia paresthetica can be divided into two main groups: (1) idiopathic, in which no clear etiology is present, and (2) symptomatic, in which the irritation of the nerve appears to result from other pathological processes.

The attributed causes can be divided into general and local.7,8

The latter, according to their localization in relation to the course of the nerve, may be:

  1. Intra- or paravertebral—when the causative agents act on the spinal cord, the roots of the nerve, or lumbar plexus in the vertebral canal, intervertebral foraminae, or in the vicinity of the vertebral column.

  2. Abdominal—when they act on the nerve during its course in the iliac fascia, as far as the inguinal ligament.

  3. Peripheral—when the causes are localized in the peripheral part of the nerve, under or distal to the inguinal ligament.

The causes most frequently mentioned in the literature7,8,17,30 in connection with the etiology of meralgia paresthetica are summarized in Table 1.

TABLE 1
TABLE 1

In certain surgical and autopsy cases of meralgia paresthetica an enlargement of the lateral cutaneous nerve has been observed.22,26,28 Stookey26 noted the sharp angulation of the nerve and stressed the tension to which it is submitted, and Lee16 obtained great improvement in a case of meralgia paresthetica by removing the “angle turn” of the nerve through a slot made in the iliac bone. They considered these factors and the trauma of movement to be responsible for the development of the condition. This opinion was also shared by Corlette.5

It may well be that in some cases, because of individual anatomical peculiarities or particular susceptibilities, the irritation of the nerve is more intense, so that not only is there proliferation of fibrous tissue, as normally found in the gangliform swellings, but also neuritis, perineuritis, and degeneration of the nerve fibers may occur as described in cases of meralgia paresthetica.1,11,13,22

Haenel11 found microscopic degeneration of the nerve in cases of meralgia paresthetica, with nodular, concentrically arranged deposits of connective tissue of a hyaline nature, arising from growth of the endoneurium. These would seem to correspond with the above-mentioned peculiar fibrous bodies found by Daniell6 in certain gangliform enlargements on other nerves.

The presence of such enlargements on the lateral cutaneous nerve of the thigh and the microscopic changes detailed above give support to the concept that mechanical friction is a cause in at least some of the idiopathic cases of meralgia paresthetica.

SUMMARY

A gangliform enlargement is described on the lateral cutaneous nerve of the thigh. It presented as a fusiform swelling in 10 cases (17 per cent) and as a progressive nonfusiform enlargement in 26 cases (43 per cent) out of 60 dissections of the nerve. It was localized in the part of the nerve crossing beneath the inguinal ligament or slightly distal to the ligament, just before the division of the nerve into its terminal branches. In this part of its course, where the nerve describes an acute angle in passing from the pelvis to the thigh, it is sometimes submitted to considerable tension, particularly in the erect posture or in extension of the thigh.

It is the mechanical friction produced by the movements of the limb on the angulated nerve that appears to be the cause of the development of the gangliform enlargements. This mechanical friction and irritation of the nerve are postulated as an etiological factor in idiopathic cases of meralgia paresthetica.

REFERENCES

Article Information

Formerly Hilel Notkovich.

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Headings

Figures

  • View in gallery

    Gangliform enlargement of lateral cutaneous nerve of the thigh. The enlargement is spindleshaped, and localized in that part of the nerve passing from the pelvis to the thigh, just in front of the anterosuperior iliac spine. The nerve and swelling have been slightly raised by means of forceps.

    l.c.n.—lateral cutaneous nerve of thigh; g.e.—gangliform enlargement; i.m.—iliacus muscle; p.m.— psoas major muscle; p.m.m.—psoas minor muscle; s.m.—sartorius; s.i.a.—anterosuperior iliac spine; c.i.—iliac crest; e.o.m.—aponeurosis of external oblique muscle, reflected downwards.

  • View in gallery

    Progressive, nonfusiform enlargement of lateral cutaneous nerve of thigh. The enlargement starts proximal to the inguinal ligament and continues to expand distal to the ligament to the point where the nerve divides into its terminal branches.

    i.l.—portion of inguinal ligament; its cut ends are grasped by forceps, f.n.—femoral nerve.

    For remaining abbreviations see legend to Fig. 1.

  • View in gallery

    Diagram showing course of lateral cutaneous nerve of the thigh; lateral view. The nerve appears sharply angulated when passing from pelvis to thigh beneath the inguinal ligament; a spindle-shape enlargement is located at apex of the angulation.

    The shaded lighter part of the nerve—l.c.n. (a)—shows intrapelvic course of the nerve proximal to inguinal ligament. The darker part— l.c.n.(b)—shows course of the nerve distal to inguinal ligament.

    For remaining abbreviations see Fig. 1.

  • View in gallery

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