Fortunately, lesions of the lumbar and sacral plexuses (heretofore collectively referred to as the lumbosacral plexus) and the proximal sciatic nerve are infrequent. Unfortunately, an inappropriately conservative approach is often undertaken in patients harboring these lesions because of the suspected degree of difficulty of the surgical approach. The bony and soft-tissue confines of the peritoneal cavity, retroperitoneum, pelvis, and gluteal region result in the application of the term "no-man's-land" to the region of the lumbosacral plexus and the proximal sciatic nerve.

Indications for surgery of nerves in this no-man's-land include tumors (usually nerve sheath tumors), traumatic injuries (including penetrating, stretch, and injection injuries), and, rarely, surgery for neural ablation. Seven fundamental surgical approaches to the lumbo­sacral plexus and the proximal sciatic nerve exist. Anyone or combination of these approaches may be used to expose a specific portion of this region. A combination of approaches (discussion follows sections on each of the seven approaches listed below) may be used when a long longitudinal exposure is indicated or when a lesion exists in a transition zone from one surgical approach to another. The seven surgical approaches are as follows:

1. A wide foraminotomy approach to the proximal nerve roots (to gain access to the proximal nerve roots as they exit the dural sac and the spinal canal)

2. The lateral extracavitary approach to the spine (to expose the nerve roots within the spinal canal, as well as approximately 4-6 cm lateral to the neuroforamina)

3. The anterolateral extraperitoneal approach to the spine (to expose the proximal mid- to lower-retroperitoneal lumbar region)

4. The pelvic brim extraperitoneal approach (to expose retroperitoneal lesions located in the low lumbar region)

5. The Pfannenstiel infraperitoneal approach (to expose caudal infraperitoneal lesions within the pelvis)

6. The transperitoneal approach (to expose, for the most part, the regions approached via approaches 3-5)

7. The extrapelvic infragluteal approach (to expose the proximal sciatic nerve as it exits from the pelvis through the sciatic notch into the infragluteal space)

With an aggressive surgical approach, there is no absolute no-man's-land in the entire region of the lumbar and sacral plexuses and the proximal sciatic nerve, although regions that could be considered "relative no-man's-lands" do exist (i.e. the region of the sciatic nerve that is located within 2-3 cm of the sciatic notch). An understanding of the regional anatomy enhances one's ability to expose this region of the nervous system (several nicely done radiographic studies have enhanced the awareness of clinicians with regard to the understanding of the anatomy), In order to further enhance this understanding, the surgical approach to each of these seven regions will be discussed. A discussion of appropriate combined approaches and the indications for these surgical approaches will also be presented.

Figure 1 illustrates the lumbosacral plexus and its relationship to surrounding tissues. Figure 2 illustrates the axial anatomy of the lumbo­sacral plexus at a variety of levels. A correlation of Figures 1 and 2 should allow for an understanding of the three-dimensional anatomy of the lumbosacral plexus. The planes of dissection of several of the approaches for lumbosacral plexus exposure presented herein are illustrated in Figure 3. whereas Figure 4 illustrates the incisions used for the surgical exposures. A clear understanding of these planes is absolutely necessary before a surgical undertaking of anyone of these approaches is entertained.

Fig-1 Fig-2
Fig-3 Fig-4

 

Wide Foraminotomy Approach to the Proximal Nerve Roots

The midline exposure of the lumbar and upper sacral spine allows access to roughly the proximal 1-2 cm of the nerve roots as they exit the spinal canal, as well as the segment of the nerve root within the canal (Figure 5), One may approach this region with a lateral subperiosteal dissection, followed by a laminectomy or hemilaminectomy using standard spinal surgical techniques. The nerve root is then visualized within the spinal canal. Following further bone removal, the neuroforamina may be unroofed and the nerve root followed distally for approximately 1-2 cm. A more lateral approach with extensive lateral paraspinous muscle retraction or splitting with soft-tissue dissection can be performed without the removal of the facet joint. This gains access to the more distal aspect of the nerve root approachable from this operation. The preservation of the integrity of the facet joint should be accomplished when possible. Subsequent degenerative changes, instability, and pain may be related to excessive bone removal in this region. If the facet joint is disrupted, the performance of a spinal fusion (either interbody or lateral) is a consideration. The advantages of the wide foraminotomy approach to the posterior spine include the familiarity of the region to spine surgeons and the relatively uncomplicated nature of the surgical exposure. The disadvantages of this approach include its limited exposure. Only the very proximal portion of the nerve root is accessible by this approach.

 
Fig-5

 

Lateral Extracavitary Approach to the Proximal Lumbosacral Plexus

The lateral extracavitary approach to the spine can be used to gain access to the first 6 cm of the extradural lumbar nerve roots (Figure 6). All regions of the thoracic and lumbar spine can be approached with this operation, although surgical exposure of the lower lumbar region via the lateral extracavitary approach requires significant dorsal ilium resection. The three-quarter prone position is preferred by this author because it facilitates visualization of the surgical field by the surgeon. It simultaneously minimizes blood loss (due to lessened abdominal compression).

The spine is approached through either a midline-oriented hockey-stick flap incision or through a paramedian longitudinal incision. A paramedian longitudinal incision is perhaps most appropriate for nerve exploration. Midline spinal exposure is not required for this operation; therefore, the creation of a cutaneous flap, with all its attendant risks, is not warranted. The thoracodorsal fascia is incised following its exposure. The erector spinae muscle is reflected medially following separation from the quadratus lumborum muscle. A well-defined plane exists between these two muscles (the middle layer of the thoracolumbar fascia). This plane is fol­lowed medially, allowing exposure of the transverse processes. Subperiosteal dissection along the underside of the transverse process allows one to follow the under surface of the transverse process, along the pedicle and the vertebral body, without fear of injury to the nerve roots as they exit the spinal canal. Following this exposure, the nerve roots can be isolated as they exit from the neuroforamina into the psoas muscle. This exposure is difficult due to the requisite muscle splitting. The nerves do not course between tissue planes in this region, thus necessitating the aforementioned muscle splitting. Further retraction laterally will allow access to the first 6 cm of the nerve after its exit from the spinal canal.

The advantages of this approach include the lack of intrapelvic dissection required and the ability to extend the dissection farther laterally than allowed with a wide foraminotomy approach. The disadvantages include the difficulties of dissecting across tissue planes and the resultant soft-tissue trauma incurred.

 
Fig-6

Anterolateral Extraperitoneal Approach

The anterolateral extraperitoneal approach to the upper lumbar spine is essentially the same approach used by surgeons to gain access to the sympathetic chain in the lumbar paravertebral region (see Figure 4). This exposure (Figure 7) allows access to the L3-5 nerve roots from their exit point from the spinal canal to below the pelvic brim (although with greater difficulty, the upper lumbar nerve roots may be exposed). The patient is positioned so that the lumbar region is extended with a log roll and the patient rotated away from the side of the exposure. The incision courses from the lateral half of the twelfth rib in an anterior and medial direction. It is extended to below the level of the umbilicus, just lateral to midline and medial to the anterior superior iliac spine. Retraction is maintained with self-retaining and hand-held retractors. Retraction always should be performed with blunt instruments.

The dissection proceeds in an anatomic manner by muscle-splitting incisions through the external oblique, internal oblique, and transversalis muscles along the muscle fibers of each muscle layer. It must be kept in mind that as each anatomic layer is passed, the surgical field becomes smaller; therefore, the incision through each of the planes (especially the more superficial planes) should be longer than one might expect so that an adequate field of exposure is available when encountering the deep structures of concern. If exposure is of utmost importance, the internal oblique and transversus abdominus muscles may be incised across their muscle fibers in the same oblique direction as the skin incision.

Following the entrance into the extraperitoneal space, the peritoneal contents are mobilized medially with the dissection remaining medial and posterior to the peritoneum and the renal fascia. Finger dissection or a sponge stick may be used to sweep the tissues away from the quadratus lumborum muscle, psoas muscle, and vertebral bodies. The lumbar veins and arteries may be obstacles to very medial dissection in the region of the neuroforamina. Their ligation may be necessary for adequate exposure. The preoperative performance of a spinal angiogram, in these circumstances, may be prudent. The sacrifice of an important spinal radiculomedullary artery could be catastrophic.

If high lumbar exposure is necessary, the diaphragmatic crus may be separated from the anterior longitudinal ligament of the vertebral column. The sympathetic chain can be visualized in the groove between the psoas muscle and the vertebral body. The upper branches of the lumbosacral plexus can be visualized as they emerge from underneath or through the psoas muscle. The main branch of the lumbar plexus, the femoral nerve, rests between the psoas and iliacus muscle as it courses toward the pelvic floor. A number of the upper branches of the lumbar plexus also can be visualized in this region. These include the lateral femoral cutaneous. iliohypogastric, ilioinguinal and genitofemoral nerves. The latter nerve is observed as it emerges medially through the psoas muscle belly. The lateral femoral cutaneous, iliohypogastric, and ilioinguinal nerves emerge either through the lateral aspect of or from underneath (and lateral to) the psoas muscle belly. These nerves may be followed proximally through the psoas muscle belly to the neuroforamina if necessary. Distal exposure is limited through this approach. The advantages of this approach include the straightforward nature of the exposure, which is familiar to most spine and vascular surgeons; however, it offers a disappointingly narrow longitudinal exposure. This exposure is limited superiorly by the crus of the diaphragm and inferiorly by the pelvic brim. Through this approach, it is also difficult to expose the neuroforamina without psoas muscle retraction (which is difficult) or resection.
Fig-7

 

Pelvic Brim Extraperitoneal Approach

The approach to the intrapelvic portion of the lumbosacral plexus is challenging. As for most of the techniques already described, the exposure is defined in the spine literature for approaches to the spine and is adapted for exposure of the lumbosacral plexus (Figure 8). The patient is positioned in an extended position with the log roll placed under the lower lumbar region on the side of surgery. This extends the lumbopelvic region and thrusts the anterior pelvic brim on the affected side forward. It therefore increases the visualization gained by the exposure and places the lumbosacral plexus in closer proximity to the surgeon. An incision beginning lateral to and slightly above the anterior superior iliac spine can be carried medially and inferiorly, and parallel and cephalad to the iliac crest and inguinal ligament. This gains access to the muscular plane below this level. An incision along the external oblique muscle fibers and across the internal oblique and transversus abdominus muscle fibers, in turn, gains access to the extra­peritoneal pelvic structures. Extraperitoneal structures are swept from the pelvic floor posterior to the peritoneum and renal fascia. The nerves of the lumbar plexus are observed emerging from between the psoas and iliacus muscles (lateral femoral cutaneous, ilioinguinal, iliohypogastric, and femoral nerves) and medial to the psoas muscle (genitofemoral and obturator nerves). The obturator nerve may be located distally by palpation at its point of exit from the pelvis through the obturator foramen and more proximally by medial retraction of the iliac vessels. The proximal sacral plexus (i.e. L4 and L5 nerve root contributions) may be visualized following lateral psoas muscle retraction and medial iliac vessel retraction. More superficially and laterally, the lateral femoral cutaneous nerve may be visualized. Exposure of this nerve in this region may be required for the surgical treatment of meralgia paresthetica.

The advantages of this approach include the relatively good exposure of the intrapelvic lumbar plexus from an anterior and lateral orientation. On the other hand, it offers a limited overall exposure, and the intrapelvic sciatic nerve and lower sacral plexus are difficult, if not impossible, to adequately visualize through this approach.

 

Fig-8

Pfannenstiel Infraperitoneal Approach

The Pfannenstiel approach gains access to the lower pelvic lumbosacral plexus as the femoral, obturator, and sciatic nerves exit from the pelvis. The approach is illustrated in Figure 9. It is a very demanding approach with limited exposure often realized. An 8 cm horizontal paramedian excision is made in the suprapubic region. It starts at the midline and extends laterally. The lateral aspect of the rectus abdominus muscle is isolated through a ventral incision in the sheath of the rectus. The rectus abdominus muscle is retracted medially. The posterior aspect of its sheath is then incised. This incision is extended laterally, gaining access to infraperitoneal structures. The sweeping of the soft tissues of the lower pelvis is performed in a similar manner as previously described with blunt retractors used to assist in obtaining and maintaining the exposure. Care is taken to protect the ureter and bladder. Obviously the bladder needs to be decompressed with a Foley catheter prior to this surgical procedure in order to facilitate exposure. Similarly, complete muscular relaxation is mandatory. The sciatic nerve, as it exits the pelvis, can be isolated underneath the psoas muscle (psoas muscle resection may be required as discussed in the previous section). The femoral nerve, likewise, is visualized as it rests between the psoas and iliacus muscles. The obturator nerve can be visualized as it passes toward the obturator foramen medial to the psoas muscle and lateral to the iliac vessels, through this exposure.

Primary nerve repair of branches of the lumbar plexus is difficult and the sacral plexus impossible in this region because of the limited and deep exposure. Ablative procedures, such as obturator and femoral nerve neurectomies, as well as the resection of nerve sheath tumors, however, are reasonably approached through this exposure.

This approach offers access to the deep pelvic paramedian structures. Its disadvantages are obviously the degree of difficulty associated with this exposure and the limited visualization gained. The farther one delves into the lower limits of this exposure, the greater the demands on the surgeon become.

 

Fig-9

Transperitoneal Approach

Much of the exposure achieved by the previous three techniques may be realized via the transperitoneal approach (Figure 10). Following the performance of a standard midline laparatomy incision and entry into the peritoneal cavity, the small intestine is packed in the upper abdomen and retracted to the right. The sigmoid colon is retracted laterally and a longitudinal incision is made in the posterior peritoneum in the midline so as to expose the desired aspect of the retroperitoneal space. Occasionally the left nerve roots cannot be seen easily in this manner, and the colon may be retracted medially and mobilized from left to right after incision along the line of Toldt. Care should be taken to avoid injury to the ureters.

A horizontal low abdominal incision also may be used. This incision extends from just medial to one anterior superior iliac spine to just medial to the other. This incision should arc slightly inferiorly and then rise to its terminus on the opposite side (concave cephalad). The rectus abdominus muscles are transected transversely. This incision may give a slightly wider exposure to caudal structures. The sacral promontory is a consistent, easily identifiable landmark that should be used to identify the L5-S1 interspace.

An excellent exposure of the retroperitoneal space is achieved through the transperitoneal approach. Lower retroperitoneal structures are more accessible than the more proximal structures (especially those on the right due to the limitations created by the presence of the sigmoid colon), such as the proximal ilioinguinal, iliohypogastric, or genitofemoral nerves. The disadvantages include the requirement for a laparotomy and the potential for neural and vascular injury. The approach, however, is very useful when a wide exposure is needed such as for tumors of neural origin.

 

Fig-10

Extrapelvic Infragluteal Approach

The extrapelvic proximal sciatic nerve can be approached easily utilizing the surgical exposure illustrated in Figure 11. The patient is placed in the prone, semi-flexed position. A question mark or reversed question mark incision along the lateral aspect of the gluteus maximus muscle is made, is extended to midline underneath the inferior aspect of the muscle, and then is extended distally along the posterior midline of the thigh (as dictated by the length of exposure of the nerve required. The skin and gluteus muscles (gluteal lid) are then elevated as a unit (without separating the skin from the gluteus muscles). In order to elevate the flap, the gluteus muscle attachments to the femur must be incised. This incision is performed close to the femur itself, leaving enough length of the ligamentous attachments to the bone so that closure is facilitated. The extent of the reflection of the gluteus muscles from their femur attachments is again dictated by the proximal extent of the lesion being approached. The sciatic nerve lies deeply within the folds between the hamstring mus­cles. After the isolation of the nerve, the nerve is followed proximally. This is assisted greatly by the reflection of the gluteal lid medially. The nerve is followed proximally, with care taken to avoid injury to the inferior gluteal artery. This can result not only in ischemic complications but can be an extremely annoying intraoperative problem. This nerve is then followed as it passes under the piriformis muscle. The muscle may be incised to gain additional cephalad exposure. The surgeon must be aware that the nerve may pass through the piriformis muscle. Further dissection immediately dorsal and adjacent to the nerve can expose the nerve more proximally as it passes into the pelvis.

The cephalad portion of the sciatic nerve is extremely difficult to expose for nerve repair purposes. Surgical treatment of the piriformis syndrome, sciatic nerve entrapment, tumors, and nerve repair, is facilitated by this approach. A combined approach for tumor resection at the superior extent of exposure of this procedure and the inferior extent of the exposure from the Pfannenstiel infraperitoneal or the anterior transabdominal laparotomy exposure will allow access to most lesions in this region (see next section). The advantages of this approach are its wide exposure of the proximal extrapelvic sciatic nerve. Proximal to the piriformis muscle, however, the exposure is prohibitively difficult.

 

Fig-11

Combined Approaches

The combined approach using the Pfannenstiel infraperitoneal and the extrapelvic infragluteal approaches can be used to gain access to the "relative no-man's-land" existing in the lower pelvis. This requires, however, two different surgical procedures and two different patient positionings; therefore, simultaneous exposure cannot be entertained. Obviously, this is associated with significant problems if, for example, the pull-through of a nerve graft is desired, This should rarely, if ever, be required because primary nerve anastomoses or cable graft anastomoses for the proximal sciatic nerve are associated with a very low success rate. This, therefore, leaves only tumor resection, ablative procedures, and neurolysis procedures as indications for exposure of this relatively difficult-to-expose area of the nervous system.

The Pfannenstiel infraperitoneal and the pelvic brim extraperitoneal approaches can be used in combination and at the same time in order to gain access to deep pelvic lesions. The exposure in this region, although not as difficult as the exit zone of the sciatic nerve from the pelvis, is nevertheless challenging. Fortunately, exposure of the nerves in this region is limited almost solely to neurolysis procedures, tumor resections, and ablative procedures.

The combination of the anterolateral extra­peritoneal and the pelvic brim extraperitoneal approaches would be appropriate for pathology traversing the boundaries of these two surgical approaches. The longitudinal exposure obtainable with the combination of these approaches is substantial. Such an extensive exposure, however, seldom would be necessary.

Similarly, the overlap between the proximal exposure of the anterolateral approach and the lateral extracavitary approach is extensive. A combination of these two approaches, therefore, seldom would be indicated. This is especially fortunate since two separate incisions with two separate surgical positionings would be required (as is the case with the extrapelvic infragluteal and Pfannenstiel infraperitoneal approaches).

For proximal lesions (especially those involving the spinal canal or intradural structures), a combined approach using the wide foraminotomy and the lateral extracavitary approaches is indicated. The combination of these two approaches is easily facilitated by the flap incision or perhaps, more appropriately, by a paramedian vertical incision. The paramedian vertical incision diminishes the chance of skin-flap vascular complications and healing problems while allowing ready access to both regions. Another advantage of the combined approach is that the facet joint usually can be left intact if an aggressive distal exposure via the lateral extracavitary approach and a proximal exposure via a wide foraminotomy are performed.

The transperitoneal approach alone offers a wide anterior midline exposure as well as many of the advantages of some of the combined approaches mentioned previously. If the risks associated with this technique offset the combined risks of the two or more individual approaches used in a combined approach, then the transperitoneal approach may be the best option.

Complications

The complications that may be encountered during or following the surgical approaches to the lumbosacral plexus are numerous. Perforation of the vena cava, aorta, iliac vessels, or lumbar arteries and veins may be catastrophic or, at the very least, a significant nuisance. Singultus secondary to intraoperative diaphragm manipulation may be disconcerting to both the patient and physician. Similarly, wound dehiscence or hernia may cause significant morbidity.

Retroperitoneal dissection may result in disruption of vital structures located in this space, such as vascular structures (as mentioned before) and urogenital structures. A knowledge of the whereabouts of important structures, such as the ureter, is of paramount importance during exposure of anatomic regions where these structures may be injured. In cases where the dissection is complicated by extenuating factors, such as prior radiation therapy, surgery, or extensive tumor bulk, the preoperative placement of a ureteral stint by an urologist may allow the intraoperative identification of the ureter. This may prevent a potentially catastrophic ureteral injury.

Finally, injury to radiculomedullary spinal arteries may result in paraplegia. Appropriate diagnostic avenues (such as angiography) must be used when such an injury may result from the surgical exposure. Alterations of surgical technique must be entertained if angiography demonstrates the presence of a radiculomedullary spinal artery in the region of planned dissection.

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