Chapter 42 Sacral Tumor Resection and Reconstruction
Most tumors of the sacrum are benign aggressive lesions (e.g., aneurysmal bone cysts, osteoblastomas, and giant cell tumors) or low-grade malignancies (e.g., chordoma or chondrosarcoma). Intralesional resections in the form of curettage provide a complete cure for benign lesions. In contrast, wide resections are necessary for complete disease control in malignant tumors. Surgical procedures for sacral tumors are classified into four types on the basis of extension of tumors and the level of sacral resection (Fig. 42-1).
Low sacral tumors, neoplasms affecting levels inferior to the S2, are approached posteriorly, whereas high sacral tumors, neoplasms affecting the S1 and S2, are approached by combined anterior and posterior incisions.1
This approach is suitable for lower sacral tumors whose superior limit can be reached on digital rectal examination (Fig. 42-2). A purse-string suture is performed around the anus. A modified knee-chest position is set, and a midline skin incision is made. The skin and subcutaneous tissue are prepared and reflected, exposing the sacrum, the sacroiliac ligament, the origin of the gluteus maximus, and the medial attachment of the sacrotuberous ligament. The sacral periosteum should not be incised or dissected.3 These ligaments and muscles are divided on both sides close to their sacral attachment. The insertion of the gluteus maximus muscle is cut up to the edge of the sacroiliac joint (Fig. 42-3).
At the deeper level, the piriformis muscle and the sacrospinous and anococcygeal ligaments are found and divided. The rectum is gently detached from the presacral lamina and from the tumor, which always protrudes anteriorly. The upper level section of the sacrum is decided on the basis of radiological findings. At the chosen level, a careful digital dissection of the anterior soft tissue is performed on both sides through the greater sciatic notch below the lower margins of the ilium and alae of the sacrum. The bulky tumor usually remains well covered by the periosteum, and careful finger dissection prevents dramatic injury to the gluteal vessels (Fig. 42-4). The pudendal nerves exiting the greater sciatic foramen and reentering the lesser foramen also should be identified and protected, except when they are too intimate with the tumor to be spared (see Fig. 42-4).
The lower roots, including S3, are removed en bloc with the tumor mass. The removed specimen includes the sacrum, coccyx, lower sacral roots, and resected surrounding soft tissue. An osteotomy is performed between the S2 and S3 dorsal foramina.4
The tumor mass is freed circumferentially and can be removed en bloc. Bleeding from the sacral stump is controlled with bone wax. Bleeding in the presacral soft tissue may be severe. The median and lateral sacral arteries and veins are usually the main sources of this bleeding. In these types of resection, reconstruction is not necessary because the sacroiliac joints are not excised. For smaller lesions of the mid-sacrum and distal sacrum, the resection of the sacroiliac joint is not required.3 Wound closure generally can be achieved without a rotational flap or other reconstructive procedures.
It is impossible to dissect the soft tissue of the upper presacrum safely via the posterior approach. A posterior approach to the upper sacrum may cause major vascular injury or inadvertent entry into the rectum, or violate the tumor capsule during an attempt to osteotomize the ventral sacrum and sacroiliac joints from behind.
With the patient supine, the anterior aspect of the sacrum is exposed through a midline vertical incision along the rectus abdominis muscle through all the layers of the abdominal wall except the peritoneum (Fig. 42-5). The internal iliac artery along with the medial, lateral sacral vessel are ligated and divided on both sides. The ligation of the internal iliac vein can cause congestion of the pelvic and epidural venous plexus. Currently, instead of ligating the internal iliac vein, the segmental veins entering the sacral foramina are ligated while exposing the anterior surface of the sacrum.5
The presacral fascia is not opened.1 The L5–S1 disc is incised and reamed. The mobilized vessels and iliopsoas muscle are retracted, and the nerve root of L5 and the iliolumbar trunk are identified. A chisel cut is made through the internal lamina of the iliac wing 1 cm lateral to the sacroiliac joint bilaterally, marking the level of resection (Fig. 42-6). The lumbosacral nerve trunks from L4 and L5 should be preserved. The S1 through S4 nerve roots are cut on both sides away from the tumor. The rectum is mobilized by blunt finger dissection in the presacral space.
The patient is set in a prone position. A three-limbed, star-shaped skin incision is used and a lumbosacral flap is lifted from the sacrum and retracted rostrally (Fig. 42-7). The posterior iliac crest, greater sciatic foramina, and sciatic nerves are exposed bilaterally, as well as the L3–5 spinous process, facet joints, and transverse process. The sacral nerve roots are divided after the L5, S1 laminectomy. The dural sac is transected caudal to the L5 nerve roots and ligated with nonabsorbable sutures. The detachment of the L5–S1 disc from the L5 endplate is completed via a posterior approach (Fig. 42-8). The L5–S1 facet joints are disarticulated. The sacrospinalis muscles are transected transversely. The gluteus maximus and piriformis muscles are divided. The dorsal sacroiliac, sacrotuberous, and sacrospinous ligaments are detached or transected. The superior gluteal vessels and nerves, inferior gluteal vessels and nerves, sciatic nerve, pudendal nerve, and posterior femoral cutaneous nerve should be preserved.