The posterior 1 surgery (▶ Fig. 17.1) is a paraspinal approach that was originally described as an alternative conduit to the lumbar spine. It went between the lateral board of the erector spinae muscles and the quadratus lumborum muscle and was first described in 1959 by Watkins. 2 However, in 1973, Wiltse modified it via a muscle-splitting sacrospinalis technique. The approach has largely been used for far lateral disc herniations, instrumented lumbar fusion, or foraminal decompression. Here, it is described in regard to pathologies of the lumbosacral plexus.
Fig. 17.1 Axial T2-weighted MRI showing a mass within the left psoas muscle. The mass can easily be approached via a left paraspinal1 approach (arrow).
The Wiltse approach allows the proximal aspect of the lumbosacral plexus (i.e., the spinal nerves) to be visualized. Thus, the indications are for proximal pathologies. This often primarily involves tumors, but can also include traumatic avulsions.
17.2.2 Case Example
A 33-year-old woman had a 2-month history of left anterior thigh pain in an L2 and L3 distribution. Her pain was shooting and shocklike, but did not reach her knee. These episodes of pain occurred 20 to 30 times a day. Motor examination revealed left iliopsoas with a Medical Research Council (MRC) grade 4 and left quadriceps 4, otherwise 5 throughout. Sensation was intact to light touch. Deep tendon reflexes were symmetric at 2+ for the ankle jerk and 3+ for the knee jerk. Magnetic resonance imaging (MRI) of the lumbar spine as shown in ▶ Fig. 17.2 revealed a left L2–L3 nerve sheath tumor extending from the L2 foramen. The mass was enhanced with contrast. The patient was scheduled for surgery via a left posterior paramedian approach for resection of what appeared to be a nerve sheath tumor. Another small intradural tumor was considered asymptomatic and was left for surveillance.
Fig. 17.2 (a, b) Sagittal and axial T2-weighted MRI demonstrating a left nerve sheath tumor extending from the L2–L3 foramen. (c) Axial and sagittal T2-weighted MRI shows complete surgical resection.
17.2.3 Surgical Technique
General anesthesia was induced with the airway secured via an endotracheal tube. The left lower extremities were monitored by electromyography (EMG). The patient’s head was placed in pins and she was positioned prone on a Jackson table. The level was localized using a spinal needle and lateral fluoroscopy. The incision was marked to the left of midline overlying the area of the transverse processes of L2 and L3. The back was prepped and draped in the usual sterile fashion.
An incision was made and dissection proceeded with monopolar electrocautery down to the level of the dorsal lumbar fascia. The fascia was divided sharply with a 15 blade through both layers, and then the cut was completed with scissors. Serial dilators were then used to dissect through the paraspinal muscles and an expandable tubular retractor was used to dock on the left L2–L3 facet. Fluoroscopy was used to confirm positioning of the tube, and then it was secured to the operating table. Alternatively, other deep self-retaining retractors can be used.
The transverse processes of L2 and L3 were exposed using monopolar electrocautery and the intertransverse membrane was opened. Soft-tissue dissection revealed the tumor. Stimulation was used to test for functional nerve fascicles. Only fascicles entering and exiting the tumor were sacrificed and the tumor was dissected free from the remaining nerves. Kerrison punches were used to take portions of the L2 left transverse processes to facilitate exposure of the tumor and nerve root.
Once the tumor was adequately circumferentially dissected, it was removed and sent to pathology for a permanent specimen. The surgical field was copiously irrigated with antibiotic saline and meticulous hemostasis was obtained. The layers of the lumbodorsal fascia were then closed together and the skin and subcutaneous tissues were closed in multiple layers with interrupted sutures.
Postoperative MRI demonstrated complete surgical resection as demonstrated in ▶ Fig. 17.2. Clinically, the patient no longer had any shooting pain in her left thigh. She did complain of burning pain in the left anterior thigh, as well as allodynia that responded to medication. Motor examination was more stable after than before surgery. She had new diminished light touch sensation over the left anterior thigh in an L2 distribution.
17.3 Transpsoas Approach
Lateral approaches through the psoas muscle have primarily been used for both open and minimally invasive spine surgery. The same approach can be used for lumbosacral plexus pathologies. The technique is a lateral retroperitoneal exposure of the psoas muscle and within it the lumbosacral plexus, as shown in ▶ Fig. 17.3.
Fig. 17.3 Coronal T1-weighted MRI with contrast reveals a multifocal nerve sheath tumor of the left lumbosacral plexus. This was best approached via a left retroperitoneal transpsoas approach (arrow). This case would not be well served by a posterior approach since the tumor extends caudally in front of the sacroiliac joint.
17.3.2 Case Example
A 49-year-old man presented to the Neurosurgery Clinic following the discovery of a left-sided mass associated with his lumbosacral plexus, as demonstrated in ▶ Fig. 17.4. At the time, he was asymptomatic. Additional imaging revealed a mass in the left internal auditory canal suggesting a schwannoma. On general examination, he had multiple subcutaneous masses but full strength throughout and sensation was grossly intact. On the basis of all these findings, it was believed that he had neurofibromatosis type 2. Surgery was recommended for resection of the left lumbosacral mass owing to its large size.
Fig. 17.4 MRI with gadolinium of the (a) lumbar spine coronal and various axial levels: (b) L3, (c) L4, (d) L5, (e) S1. These demonstrate what are probably multiple left paraspinal masses coalescing into one large mass with involvement of the left L3–L4, L4–L5, and L5–S1 nerve roots into the neural foramina without intradural extension.
17.3.3 Surgical Technique
The patient was placed under general endotracheal anesthesia supine on the operating room table. A bump was placed under the patient’s left buttock and back. This could also be done in a full lateral position. Needles were placed for EMG monitoring during surgery.
Although a direct lateral approach could have been performed, the access surgeon here opted for an oblique approach. An oblique incision approximately 10 cm long was made over the left part of the lower abdomen. Scarpa’s fascia was opened. The anterior rectus sheath was divided. The rectus muscle was mobilized medially. The abdominal wall was divided into layers and the retroperitoneum entered. Retroperitoneal contents were retracted medially including the left colon, left kidney, left ureter, left iliac artery, and left iliac vein. Care was taken to identify all these structures and avoid injuring them. At this point, retractors were placed using the wishbone-type table-affixed general surgery retractor. It was then easy to identify the spine and the tumor within the psoas muscle. This was first identified by palpation through the psoas muscle, and then once the muscle fibers had been split, the tumor was easily visualized. We then started to dissect it.
Initially, we focused on the most rostral and medial of the five masses. We dissected around the tumor, stimulating intermittently with the nerve stimulator. The capsule surrounding the tumor was opened, and then we dissected circumferentially. The most rostral aspect of the tumor was removed piecemeal. We then proceeded from rostral to caudal, resecting each tumor in the same fashion, dissecting around them, stimulating intermittently any time we had to cut. After we had dissected around all the masses and resected them, we palpated throughout the psoas muscle. No other masses could be palpated.
The psoas muscle did not need reapproximation. The abdominal contents were returned to their anatomical locations. The abdominal wall was closed in layers with 0 PDS suture (Polydioxanone, Ethicon, Johnson & Johnson) and 3–0 Vicryl (Ethicon, Johnson & Johnson) for the subcutaneous Scarpa’s fascia and 4–0 PDS for the skin. Steri-Strips (3M) were applied. A routine postoperative abdominal X-ray was obtained and ruled out any retained instruments.
Postoperatively, the patient’s strength in the left iliopsoas was 4/5 but improved over time to 5/5. He also developed decreased light touch sensation over the left L4 distribution. Pathology revealed schwannomas.
17.4 Anterior Muscle-Splitting Approach
The anterior approach began with approaches to the lumbar spine by Müller in 1906, while anterior lumbar interbody fusion was introduced during the 1930s. 3, 4 These were first described as anterior transperitoneal approaches. These anterior approaches had soon evolved to be retroperitoneal, very much like the lateral approach. The difference between these two approaches is the trajectory as depicted in ▶ Fig. 17.5. With the anterior approach, the ventral aspect of the spine and lumbosacral plexus can be identified. This approach has been adopted for surgical treatment for patients with meralgia paresthetica who have failed lateral femoral cutaneous nerve decompression. Alberti et al 5 depict a suprainguinal, anterior, retroperitoneal approach for these pathologies.
Fig. 17.5 Left anterior (arrow) muscle-splitting retroperitoneal approach to the lateral femoral cutaneous nerve. ASIS, anterior superior iliac spine.