Most tumors of the sacrum are benign aggressive lesions—aneurysmal bone cysts, osteoblastomas, and giant-cell tumors—or low-grade malignancies, such as 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. 55-1 ).
Type I is low sacral amputation, or sacrectomy below S2
Type II is high sacral amputation, or sacrectomy through S1 or S1–S2
Type III is total sacrectomy, or sacrectomy through L5–S1
Type IV is extended sacrectomy, or total sacrectomy combined with excision of the ilium, vertebra, or intrapelvic organs
Low sacral tumors, neoplasms that affect levels inferior to the S2 disk, are approached posteriorly, whereas high sacral tumors, neoplasms that affect the S1 and S2 disks, are approached by combined anterior and posterior incisions.
Tumors Involving S3 and Below
This approach is suitable for lower sacral tumors whose superior limit can be reached upon digital rectal examination ( Fig. 55-2 ). A purse-string suture is done 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 to expose the sacrum, sacroiliac ligament, origin of the gluteus maximus, and medial attachment of the sacrotuberous ligament; the sacral periosteum should not be incised or dissected. 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. 55-3 ). This allows exposure of the inferior roots of the sciatic nerves, piriformis muscle, and posterior margin of the pelvic portion of the tumor.
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 radiologic 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 avoids dramatic injury to the gluteal vessels. The pudendal nerves exiting the greater sciatic foramen and reentering the lesser foramen should also be identified and protected, except when they are too intimate with the tumor to be spared ( Fig. 55-4 ).
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.
The tumor mass is freed circumferentially and can be removed en bloc. Bleeding from the sacral stump is controlled with bone wax, and 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 resections, reconstruction is not necessary, because the sacroiliac joints are not excised. For smaller lesions of the midsacrum and distal sacrum, resection of the sacroiliac joint is not required. 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 it may violate the tumor capsule during an attempt to osteotomize the ventral sacrum and sacroiliac joints from behind. These difficulties are best addressed by combining the dorsal sacrectomy via a ventral approach for lesions that require amputation through the level of the sacroiliac joints.
Tumors Involving Proximal Sacrum (Combined Anterior and Posterior Approach)
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. 55-5 ). The internal iliac artery along with the mediolateral 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 plexi. 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.
The presacral fascia is not opened. The L5–S1 disk 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 S1 joint bilaterally, marking the level of resection ( Fig. 55-6 ). 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 is retracted rostrally ( Fig. 55-7 ). The posterior iliac crest, greater sciatic foramina, and sciatic nerves are exposed bilaterally as are the L3–L5 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 is ligated with nonabsorbable sutures. The detachment of the L5–S1 disk from the L5 end plate is completed via a posterior approach ( Fig. 55-8 ). The L5–S1 facet joints are disarticulated. The sacrospinalis muscles are transected transversely, and the gluteus maximus and piriformis muscles are divided. The dorsal sacroiliac ligament, sacrotuberous ligament, and sacrospinous ligament 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.
In a posterior sacral osteotomy, the sacroiliac joints or ilium are cut with an osteotome or drill from behind ( Fig. 55-9 ). Bone resection with an osteotome or drill proceeds to meet the ventral osteotomy previously made. For easier cutting, a threadwire saw can be used. If indicated, the resection margin can be extended to the iliac bone. The extent of ilium resection is determined by a sagittal computed tomographic (CT) scan or magnetic resonance imaging (MRI). A shallow groove is cut through the internal cortex of the iliac wing lateral to the sacroiliac joint to mark the level of resection ( Fig. 55-10 ). In the case of an iliac bone resection, the iliac vessel dissection should be complete when a ventral sacrectomy is performed.
A 55-year-old woman came to medical attention with a painful mass in her left buttock. CT scan showed that the mass was destroying the lower sacrum and left iliac bone ( Fig. 55-11 ). The mass extended below the sacral level to the coccyx area ( Fig. 55-12 ), and the operation was done with the patient in a lateral decubitus position ( Fig. 55-13 ). The skin incision was started from the midline as a vertical shape and was extended to the left buttock as a horizontal shape (see Fig. 55-13 ).