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Introduction

Chordoma is a rare, indolent primary bone malignancy. It comprises 1%–4% of primary bone malignancies. The incidence is 0.08 in 100,000; it has a male predominance (∼2:1) and a peak presentation between 50 and 60 years. Chordoma, in originating from the notochord, occurs along the midline spinal axis from skull base to sacrum. Sacral cases account for one-third of all chordomas. Chordoma is the most common primary bone tumor of the sacrum comprising greater than 50% of all cases. Survival is poor (72% and 48% at 5 and 10 years, respectively) and dependent primarily upon en bloc surgical resection.

Evidence for Surgical Resection

The Enneking principles of musculoskeletal oncology suggest wide en bloc resection of chordoma as the preferred surgical strategy; however, this can be difficult even in the hands of the most experienced surgeons. The surgical goal of wide, en bloc resection is achieved in only 35%–81% of cases, because of sacral region anatomy, tumor size, and preference for maintaining neurological function. In a recent multicenter study, including 167 patients with sacral chordoma, the median duration of local recurrence–free survival was 4 years, with 57 patients suffering local recurrence during the follow-up period. Both previous surgery and intralesional resection were identified as predictors of local recurrence. The median duration of overall survival with a sacral chordoma is 6 years; increasing age and motor deficit predict shorter survival. Previously intralesional resection has been associated with higher local recurrence. In a retrospective, single institution experience, 43 patients with sacral chordoma underwent surgical resection. All four patients with only intralesional resection developed local recurrence and metastases, and then died of their disease. In contrast of 27 patients undergoing wide surgical excision, only 9 experienced local recurrence during the follow-up period.

Functional outcome after sacrectomy is related to the level of the nerve roots sacrificed for midline tumors: low sacral (sacrifice of at least one S4 nerve root), midsacral (sacrifice of at least one S3 nerve root), high sacral (sacrifice of at least one S2 nerve root), total (sacrifice of at least one S1 nerve root), and hemicorporectomy (translumbar amputation). In general, patients with a sacral amputation distal to the S3 nerve root (low sacral) experience limited deficits. Patients who undergo a mid- or high sacral resection experience bowel and bladder dysfunction with severity dependent on the level of sacral amputation. Total sacrectomy results in motor deficit and loss of sphincter control and sexual ability, if both S1 nerves are sacrificed. The level of sacrectomy also correlates with operative morbidity and length of hospital stay.

Surgical Technique

Posterior Approach

The patient is positioned prone. A dorsal midline or elliptical incision is planned (to incorporate previous biopsy tracts) from superior to the involved area of the sacrum to distal to the tip of the coccyx. This is carried down to the fascia and flaps are raised to the palpable edges of the sacrum or beyond the soft-tissue extent of the tumor. The fascia and fibers of the gluteus maximus muscles are divided near their origin from the posterior sacral edge. When the tumor extends beyond the bone, the dissection is guided by the palpable and radiographic extent of the tumor. The posterior iliac crest, sciatic notches, and sciatic nerves are exposed bilaterally. The piriformis muscles are divided (lateral to the tumor) exposing the superior gluteal arteries and veins at the superior aspect, and the inferior gluteal arteries and veins, sciatic and pudendal nerves at the inferior aspect. This, in general, forms the lateral borders of the resection.

The caudal pole of the sacrum/coccyx is released by incising the anococcygeal ligament proximal to the anal sphincter, the sacrotuberous ligament from the ischial tuberosity, the sacrospinous ligament from the ischial spine, and the remaining coccygeal muscles. This release facilitates dissection onto the anterior surface of the sacrum, and blunt finger dissection is used to separate the sacrum/sacral tumor from the mesorectal fascia. This Kraske approach is commonly utilized in colorectal surgery and establishes the caudal and anterior aspects of the resection.

The paraspinal muscles are truncated cephalad to the uppermost level of the tumor, and the sacrum is exposed in a subperiosteal manner from edge to edge. The dura can be identified using a standard laminectomy technique. Care must be taken to confirm that the laminectomy is performed at the appropriate level. The sacral nerves are then identified, isolated, and traced along their course. Nerves involved by tumor need to be sacrificed. The caudal-most nerves that can be preserved are traced to their respective sacral foramina. These foramina can then serve as valuable landmarks through which the sacrum can be cut while preserving the nerves. A threadwire saw, osteotome, high-speed drill, or a combination of these tools can then be used to make the bone cuts needed to amputate the sacrum at the appropriate level. A hand may be placed via the Kraske approach between the ventral tumor and rectum to guide the osteotomies and protect the pelvic contents while making the bone cuts. Once the bone cuts are made and the musculo-ligamentous attachments have been divided, the specimen can be mobilized posteriorly. The preserved nerves are dissected free, the sacrificed nerves are cut distally, and the remaining soft-tissue attachments are divided allowing the tumor to be excised ( Fig. 29.1 ).

Technique of posterior midsacral amputation. (A) sagital and (B) axial T1 MRI demonstrating a large chordoma arising below S2, note the presacral fat surrounding the tumor ( arrows ), which serves as a plane of dissection from a posterior approach (kraske technique), allowing the colorectal surgeon to separate the rectum (R) from the lesion. (C) Anatomic model and (D) intraoperative picture demonstrating a complete laminectomy of S1 and S2, note that the S2 nerve roots are dissected until its corresponding foramen ( dashed yellow line ). The thecal sac is ligated at the emergence of the S2 nerve roots ( blue line ). The lateral osteotomies are performed with a thread-wire saw (T-saw), introduced trough the S2 foramen, and recovered at the level of the sciatic notch ( green dotted lines ). The central disconnection ( white solid line ) is performed with an osteotome between the S2 foramens, while the assistant manually separates the rectum from the anterior surface of the sacrum. (E) Intraoperative picture demonstrating the placement of the T-saw trough the right S2 foramen ( arrow ). (F) The T-saw is recovered at the level of the right sciatic notch ( double arrowheads ), the other extremity of the saw emanating from the S2 foramen ( arrow ) is positioned vertically, and reciprocating movements are performed until the lateral osteotomy is completed. (G) The central osteotomy is performed with the assistant separating the rectum and vascular structures of the pelvis from the anterior surface of the sacrum (hand). A Penfield dissector demarcates the S2 foramen and an osteotome is used disconnect the sacrum between the S2 foramina. (H) The remaining soft attachments of the lower sacrum are released and the specimen is removed en bloc.

Combined Anterior–Posterior Approach

Traditionally, en bloc total sacrectomy and high sacral amputations have been performed using a staged anterior–posterior approach. The anterior approach permits the surgeon to expose the ventral aspect of the tumor, to mobilize the rectum, to identify and dissect the iliac vessels (and potentially ligate the internal iliac arteries and veins), to mobilize the lumbosacral trunks (L4 and L5 contribution to sciatic nerve), and, in the case of total sacrectomy, to perform an L5-S1 discectomy. Initiation of osteotomies, placement of threadwire saws, and other facilitation of bone cuts can also be performed via the anterior approach. Lastly, a vertical rectus abdominus myocutaneous (VRAM) flap can be harvested and placed into the pelvis for subsequent filling of the soft-tissue defect after posterior resection. All of these maneuvers reduce the potential for complications during the subsequent posterior resection and reconstruction, particularly for the upper sacral amputations where the risks of vascular injury are higher and the size of the wound defect is typically larger. The posterior approach is then used for tumor removal and spino-pelvic reconstruction as described above. For tumors extending to the S1 and S2 levels, the transverse sacral osteotomy may extend to the sacroiliac joints laterally. For total sacrectomy, an L5-S1 discectomy disconnects the sacrum rostrally. Sacroiliac osteotomies detach the sacrum laterally.

Recently, the use of the posterior-only approach has been proposed for all sacral tumors that do not extend beyond the lumbosacral junction or invade the pelvic organs. With this technique, the anterior dissection is performed once the bone cuts have been made, and the tumor is mobile enough to be retracted posteriorly. This gradually reveals the ventral dissection planes from the posterior approach. When the tumor extends through the sacroilliac joint to the iliac bone, the sacrectomy may be combined with hemipelvectomy performed in a lateral decubitus position.

The patient is positioned supine. A midline laparotomy incision is planned from above the umbilicus to just above the pubic symphysis. Although the tumor resides in the extraperitoneal space, a transperitoneal approach is often employed given the extent of dissection required. After retracting the bowel away from the surgical field, the ureters and iliac vessels are dissected. The rectum is mobilized away from the tumor. The middle sacral arteries and veins are ligated. We commonly divide the internal iliac arteries and veins bilaterally as this dramatically facilitates mobilization. Elevating these vessels off of the ventral aspect of the sacrum and pelvis decreases the likelihood of injury during the completion of the bone cuts performed during the posterior stage of the operation. Mobilization of these vessels also enhances access to the lumbosacral trunks (the L4, L5 contributions to sciatic). These nerves must be freed from the anterior surface of the sacrum. With these soft-tissue structures mobilized, steps can be performed to facilitate the osteotomies. The location of these bone cuts are guided by the ventral sacral foramina and extent of the tumor. For tumors not requiring total sacrectomy, the anterior aspect of the sacrum can be scored or marked with an implanted threadwire saw at the appropriate level for the amputation. In the case of total sacrectomy, the L5-S1 disc can be removed to establish the cephalad bone margin. The sacroiliac joint can be identified just lateral to the lumbosacral trunks and disarticulation of the sacrum from the ilium can be initiated with an osteotome. Completion of the sacroiliac osteotomies is performed during the second-stage posterior approach. Lastly, the anterior stage of the procedure provides a valuable option for the soft-tissue reconstruction that will be necessary after the sacrum is removed. A vertical rectus abdominus myocutaneous flap may be harvested on its inferior epigastric pedicle, and placed into the pelvis. This can be recovered during the posterior approach to fill the defect with healthy vascularized tissue. A silastic sheet may be placed between the great vessels, rectum, and tumor as a marker/protective barrier for the posterior stage of the procedure. The abdominal incision is closed in layers ( Fig. 29.2 ).

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