Surgical Management of Sacral Tumors
BACKGROUND
Tumors involving the sacrum mainly include primary and metastatic tumors.
Metastatic tumors are more common than primary ones.
The most common benign sacral tumor is giant cell tumor. The most common primary malignant sacral tumor is chordoma followed by chondrosarcoma.
Schwannoma, arising from the neural elements and not the sacrum, is categorized into the sacral tumors because it is clinically similar to other sacral tumors and treated the same way as well.
The symptoms, which are usually either nonspecific or similar to that of lumbar disc herniation, develop insidiously for months to years due to the potentially large presacral space. The tumors may become very huge before diagnosis.
A primary tumor often involving the sacrum is chordoma.1 Tumors in this anatomic location are of low grade and unlikely result in metastatic disease. Problem of local control may be made worse by tumor spill resulting from incomplete excision. Local spill of tumor cells with biopsy, or partial resection by an inexperienced surgeon, may severely compromise the opportunity for a complete recovery.
Surgical management of sacral tumors is challenging due to the rich blood supplies and complex anatomic structures (ie, nerves, vessels). It is frequently associated with high risk of local recurrence and complications.
Resections of the sacrum are not commonly performed.
Operation can be performed safely and deliberately through knowledge of the anatomy in this area and a full knowledge of the principles of dissection. Nerve roots and inferior border of the sacroiliac joints are both the risky locations for positive margins. In rare conditions, tumors may require en bloc resection of the rectum or annal canal plus rectum.
The perioperative complications may include massive intraoperative and postoperative bleeding; injury of rectum, bladder, etc.; wound complications; and neurologic dysfunction postoperatively.
In the recent years, the computer-assisted navigation technology has shown promise in aiding in optimal preoperative planning and in providing more precise and accurate tumor resection. Potentially, local recurrence may be reduced and neurologic function may be preserved at its best by applying this technology.
Radiation for residual may be helpful.
ANATOMY
Sacral Plexus and the Coccygeal Plexus
Lumbosacral trunk (L4, L5) courses over the sacral ala.
The caudal parts of the ventral branches of L4 and L5 combine to form the lumbosacral trunk (FIG 1). Together with the ventral branches of the first three sacral nerves and the upper part of the ventral branch of the fourth sacral nerve, the lumbosacral trunk forms the sacral plexus.
S1-S3 roots issue through the upper three anterior sacral foramina, the lumbosacral trunk is joined by S1 at the level of the sacroiliac joint, and S1-S5 exits the foramina sacralia pelvina.
The tip of the sacral plexus comes toward the greater sciatic foramen, lying in front of the sacrum and piriformis.
The coccygeal plexus arises from the lower part of the ventral branches of the fourth and fifth sacral nerves as well as the coccygeal nerves.
The sacral plexus provides motor and sensory nerves for the pelvic, buttocks, perineal region, the posterior thigh, most of the lower leg, the entire foot, and part of the hip joint. Except many short muscle branches for piriformis, musculus obturator internus, and quadratus femoris, the sacral plexus and the coccygeal plexus divide into the following branches.
The superior gluteal nerve (L4-L5, S1). The superior gluteal nerve, along with the superior gluteal artery and vein, departs from the pelvis via the suprapiriformis foramen. The nerve supplies the tensor fasciae latae, the gluteus minimus, and the gluteus medius muscles.
The inferior gluteal nerve (L5, S1-S2). The inferior gluteal nerve, along with the inferior gluteal artery and vein, departs from the pelvis via the infrapiriformis foramen. The nerve supplies the gluteus maximus.
The pudendal plexus. The pudendal plexus is formed by S3-S4 and portions of anterior division of S1-S2. Deep of the origin of the gluteus maximus muscle from the sacral edge, the pudendal nerve must be spared because it courses posterior to the ischial spine and then on the surface of the obturator internus in the ischiorectal fossa. It is in anterior inferior of the sacral plexus but not sharply marked off from it. It gives off the following branches. The muscular branches are derived from the fourth sacral and supply the levator ani, coccygeus, and sphincter ani externus. The visceral branches arise from the third and fourth, and sometimes from the second, sacral nerves and are distributed to the bladder and rectum and, in the female, to the vagina; they communicate with the pelvic plexuses of the sympathetic nervous system. The perineal nerve, the inferior and larger of the two terminal branches of the pudendal nerve, is situated below the internal pudendal artery. Some of the nerve fibers are distributed to the skin of the scrotum and communicate with the perineal branch of the posterior femoral cutaneous nerve. These nerves supply the labium majus in the female. The perineal nerve gives off from the nerve to the bulbocavernosus, pierces this muscle, and supplies the corpus cavernosum urethrae, ending in the
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mucous membrane of the urethra. The dorsal nerve of the penis is the deepest division of the pudendal
nerve. It gives a branch to the corpus cavernosum penis and passes forward, in company with the dorsal artery of the penis, between the layers of the suspensory ligament, on to the dorsum of the penis, and ends on the glans penis. In the female, this nerve is very small and supplies the clitoris. The fifth sacral nerve receives a communicating filament from the fourth and unites with the coccygeal nerve to form the coccygeal plexus. From this plexus, the anococcygeal nerves take origin; they consist of a few fine filaments that pierce the sacrotuberous ligament to supply the skin in the region of the coccyx.
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FIG 1 • The sacral plexus (A) and the coccygeal plexus (B) distribution.
The posterior femoral cutaneous nerve (S1-S3). It leaves the pelvis through the suprapiriformis foramen. It accompanies the inferior gluteal artery to the gluteus maximus and supplies the skin of the back thigh and the popliteal fossa.
The sciatic nerve (L4-L5, S1-S3). It is the longest and widest single nerve in the human body. The relationship between the piriformis muscle and the sciatic nerve is close and may be changing. In most instances, the sciatic nerve exits the pelvis via the suprapiriformis foramen. It then lies posterior (superficial) to the short external rotators (superior gemellus, inferior gemellus, and obturator internus). It then runs down the buttocks and the back of the thigh, giving rise to motor branches for the hamstring muscles. When the sciatic nerve reaches the apex of the popliteal fossa, it terminates by bifurcating into the tibial and common fibular nerves.
The dural sac ends at the S2-S3 junction. When dural sac is injured, cerebrospinal fluid leak will occur.
Radical resection of the entire sacrum would result, in addition to sphincteric incontinence, in considerable denervation of both lower extremities in the distribution of the sciatic nerves. Resections below the body of S3 vertebra do not endanger continence of the anal and bladder functions.
Vascular Anatomy
The blood supplies of sacral tumors mainly include internal iliac artery, internal pudendal artery, the superior
gluteal artery, the inferior gluteal artery, the vesical artery, the rectal artery, the iliolumbar artery, and the lateral sacral artery (FIG 2).
The pertinent blood supplies of sacral tumors, which might be dealt with during operation, mainly include the superior gluteal artery, the lateral sacral artery, and the median sacral artery. There are communications among the superior gluteal artery, the subcostal artery, and the intercostal artery from the abdominal aorta. The superior and inferior arteries also have anastomosis with the femoral profound artery from the lateral iliac artery. There are anastomosis between lateral sacral artery and median sacral artery as well.
Venous anatomy generally parallels arterial anatomy but is subject to a high degree of variability and could develop proliferation and enlargement due to the tumors.
Anatomy and Biomechanics of the Sacroiliac Joint
The sacroiliac joint is a synovial structure formed between the articular surfaces of the sacrum and ilium. The articular
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surface of the sacrum that conjoins with ilium is ear-shaped with complementary irregularities between the articular surfaces, which offer mechanical stability to the joint. The interosseous, anterior, and posterior sacroiliac ligaments are the strongest in this region and function to strengthen the joint.
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FIG 2 • The main blood supplies in the sacral area.
When the transverse partial sacrectomy is performed just cephalad to the S1 neural foramina and the average resection of the sacroiliac joint is 25%, the bearing capacity of the joint reduces to 35% of the normal. When the transverse partial sacrectomy is performed just caudal to the S1 neural foramina and the average resection of
the joint is 16%, the bearing capacity of the joint reduces to 72% of the normal.3
Reconstruction is not needed when performing the transverse partial sacrectomy caudal to the S1 neural foramina. Reconstruction should be considered when performing the transverse partial sacrectomy above the S1 nerve root.
Muscles and Ligaments
The gluteus maximus originates from the posterior aspect of dorsal ilium, posterior superior iliac crest, posterior inferior aspect of sacrum and coccyx, and the sacrotuberous ligament. As it passes from the sacrum to the femur, the gluteus maximus covers the sacroiliac joint and the sacrospinous and sacrotuberous ligaments as well as a portion of the ischiorectal fossa. It inserts primarily in fascia lata at the iliotibial band and also into the gluteal tuberosity on posterior femoral surface. The arterial supplies are inferior and superior gluteal arteries and the first perforating branch of the profunda femoris artery.
The piriformis is also a very important structure for sacral tumor resection. It originates from the anterior part of the sacrum, the part of the spine in the gluteal region, and from the superior margin of the greater sciatic notch. It exits the pelvis through the greater sciatic foramen to insert on the greater trochanter of the femur.
The erector spinae muscle arises from the anterior surface of a broad and thick tendon, which is attached to the medial crest of the sacrum, to the spinous processes of the lumbar, and the supraspinous ligament, to the back part of the inner lip of the iliac crests and to the lateral crests of the sacrum, where it blends with the sacrotuberous and posterior sacroiliac ligaments. Some of its fibers are continuous with the fibers of origin of the gluteus maximus.
The sacrotuberous ligament is situated at the lower and back part of the pelvis (FIG 3). It runs from the sacrum (the lower transverse sacral tubercles, the inferior margins sacrum, and the upper coccyx) to the tuberosity of the ischium. The sacrospinous ligament is a narrow ligament attached to the ischial spine and the lateral region sacrum and coccyx. Together with the sacrotuberous ligament, it converts the greater sciatic notch into the greater sciatic foramen and the lesser sciatic notch into the lesser sciatic foramen.
INDICATIONS
Surgical indications for primary benign/intermediate tumors such as giant cell tumor of bone, schwannoma, etc. Tumor resection, curettage, or a mixture is recommended. Intralesional margin is acceptable.
Surgical indications for primary malignant tumors such as chordoma, chondrosarcoma and Ewing sarcoma, etc. Tumor resection is required with wide or marginal margin.
Surgical indications for metastatic tumors. Surgical treatments should be evaluated on a case-by-case basis. Resection, curettage, and ablation are options.
Surgical indications for adjacent soft tissue sarcomas involving the sacrum. It is recommended that the tumor and the involved sacrum should be resected en bloc.
PATIENT HISTORY AND PHYSICAL FINDINGS
Chronic, dull, lower back or coccygeal pain due to chronic nerve compression is one of the most common presenting symptoms. It could be misdiagnosed as lumbar disc herniation. Some patients are diagnosed
incidentally with benign tumors, although asymptomatic.
The typical symptom of sacrum tumors is chronic lower back pain with an alteration of bowel or urinary habits due to its mass effect and compression. Ambulation dysfunction and bowel and bladder incontinence may rarely happen.
Lower sacral tumors can grow large enough for their anterior portion to be palpated during a rectal examination. Some large sacral tumors such as chordoma and chondrosarcoma present large bumps in the buttock.
Those patients with high-grade malignant tumors may suffer severe pain for weeks or months with difficulty in ambulation. Patients usually have to stay in one fixed position to alleviate the pain. The mass is frequently small even if it is palpable during a rectal examination.
IMAGING AND OTHER STAGING STUDIES
Plain Radiography
Images are often obscure and confusing especially during the early days of the disease. It is hard to arrive at a definite diagnosis with only the plain radiography in most instances.
Chordoma usually locates in the lower part of the sacrum and may be diagnosed with plain radiography in the early
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days. Lesions of giant cell tumor, simple bone cyst, and aneurysmal bone cyst, usually large and totally lytic, locate in the upper part of the sacrum and may also be diagnosed with plain radiography.
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FIG 3 • Anterior (A) and posterior (B) views of the ligaments of the sacrum.
Schwannoma in the sacrum almost exclusively originates from the anterior division of the sacral nerve. The enlarged anterior sacral foramina could be easily identified through plain radiography.
One should be aware that the diagnosis could be missed or delayed if only the plain radiography is taken.
However, plain radiography is necessary with the value of overview on the tumor, correlations with other images, and postoperative follow-up (FIG 4).
Computed Tomography and Magnetic Resonance Imaging
Computed tomography (CT) with intravenous contrast is the optimal technique for assessing the extent of bone involvement and destruction, possible ossification or calcification of the
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matrix, the anatomic location, the blood supply, and the relation between the tumor and the visceral organs (FIG 5). It is helpful in differential diagnosis of benign and malignant tumors.
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FIG 4 • A,B. Chordoma of the sacrum. (continued)
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FIG 4 • (continued) C,D. Giant cell tumor of the sacrum. E,F. Schwannoma of the sacrum.
Chest CT is essential for staging purposes in evaluation for pulmonary metastases of malignant tumors.
Magnetic resonance imaging (MRI) with contrast is critical for imaging soft tissue mass involvement and the relation between the tumor and the surrounding tissues (ie, vessels, nerves, muscles, visceral organs). MRI is the optimal modality for imaging soft tissue due to its superior discrimination ability than CT.
MRI with contrast may be helpful for the serial assessments of neoadjuvant therapy.
Bone Scan
Bone scan may sometimes detect small sacral lesions, which are not clearly identified by other radiographs. Bone scan is usually used to rule out systemic disease (ie, metastasis)
Angiography
Angiography is necessary for malignant sacral tumors.
It is essential to clearly determine the blood supplies of the tumor and the pertinent vascular anatomy with angiography for evaluation of the risk of surgical management.
Selective embolization of the tumor blood supplies before surgery is significant in minimizing blood loss during surgery (FIG 6). It has taken the place of ligation and temporary block of arteries in our institution. However, it should be recognized that excessive and large areas of embolization may increase the risks of flap complications.
Positron Emission Tomography-Computed Tomography
Positron emission tomography-computed tomography (PET-CT) may be used in assessing malignant sacral tumors, especially metastatic disease.
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FIG 5 • A,B. CT scans of a chordoma with contrast. C. MRI of a chordoma.
It is helpful for detecting multifocal lesions and monitoring for local recurrence. It is of limited value in the process of preoperative plan.
Biopsy
Biopsy is of significant value to the definitive surgical intervention. The purpose is to yield a valid tumor diagnosis (benign vs. malignant), tumor grade (high vs. low grade), and the specific tumor type.
The most commonly used technique is core needle biopsy. Open biopsy is not needed in most circumstances. The biopsy with a posterior midline entry portal at the appropriate level is most commonly performed.
Biopsy should be well planned and follow established guidelines, such as incision placement within the line of eventual resection, thus minimizing contamination of normal tissues.
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FIG 6 • Angiograph of a chordoma patient showed blood supply before (A) and after (B) embolism of the tumor.
SURGICAL MANAGEMENT
Preoperative Planning
Careful review of every preoperative imaging including x-ray, CT, MRI, and angiography is crucial to formulate a surgical plan and evaluate the indications and risks.
Upper extent of the resection should be well determined to achieve an accurate resection. The goal is to save as many sacral nerves as possible with good margins. Because the coccygeal tip could be easily exposed during operation and the exposure will not compromise the surgical margin, one recommended way of accurate resection is to measure the distance between the coccygeal tip and the level of sacral osteotomy based on the sagittal CT or MRI.
Arterial embolization is recommended within 12 to 24 hours before surgery. The vessels that were selectively embolized
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mainly include the internal iliac, the lateral sacral, the iliolumbar, and the median sacral arteries. These vessels were identified by angiography and usually embolized by Gelfoam.
Anesthetic techniques including controlled hypotension and controlled low temperature may be used to control the intraoperative blood loss for large and high-level sacral tumors.
It is never wrong to get enough blood well prepared including red blood cell, plasma, and platelet. An alternative route of blood transfusion and fluid replacement is essential to the surgery. It is important to keep monitoring the estimated intraoperative blood loss and maintain adequate communication with the anesthetist.
It is suggested that oral antibiotics are given 24 hours before surgery and cleaning enema is done 12 hours before surgery. In addition, at the time of surgery, all patients should have a Foley catheter and a rectal tube placed to provide protection for ureter, bladder, and rectum during operation.
Intensive care unit (ICU) reservation should be considered. Appropriate communications with urologists and general surgeons are important if there is colon or bladder involvement.
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FIG 7 • A. Posterior position with Y-shaped approach. B. Posterior position with transversely placed H-shaped approach. C. Lateral position with an extended McBurney incision.
Everything that might be needed during operation, including internal fixation materials, disposable hemostasis device, and other implants, should be well prepared.
Possible image fusion of CT with MRI and subsequent detailed design of surgery should be performed if computer navigation-assisted surgery is planned.
Positioning
Patient is placed in the prone position for the posterior approach.
Patient is placed in the lateral position for the anterior-posterior approach (combined abdominosacral approach).
Approach
The posterior approach: A longitudinal incision is performed through the midline from L5 to the coccyx. If the tumor is quite large, one or two transversal incisions could be added and the entire incision simulates a Y (FIG 7A) or a transversely placed H (FIG 7B).
The anterior-posterior approach (combined abdominosacral approach): It is a combination of the posterior incision and an extended McBurney incision, which starts from the lateral lowest rib and ends at the top of the pubic tubercle (FIG 7C).
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TECHNIQUES
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Sacral Tumor Resection via the Anterior-Posterior Approach
The patient is placed in the lateral position (combined abdominolateral sacral position). Usually, the left side is up, but this may be revised depending on the soft tissue component of the tumor lateral to the sacrum.
Anterior Approach
An extended McBurney incision is performed first. Through this incision, the retroperitoneal space is explored by dissecting the abdominal wall musculature. The abdominal contents are pushed to the contralateral side of the abdomen. The ureters should be well protected during this process. Then, the abdominal aorta, the iliac vessels, and the median sacral vessels are exposed.
In most cases, schwannoma could be excised with only this incision.
This incision makes it possible to reduce the risk of bleeding by ligating the internal iliac artery of the same side and temporarily block the aorta.
To ligate the median sacral vessels. The median veins are accompanied by the sacral nerve, and in front of the sacrum, they anastomose with each other to form the presacral venous plexus. It is suggested that suture ligation of the presacral venous plexus should be right above the sacral resection level. Then the venous plexus below the resection level is resected together with the sacrum. Through this management, excessive blood loss is usually avoided.
When large tumors extend anteriorly into the pelvis, careful blunt dissection of tumors from the vital vessels is essential via this incision to avoid unnecessary vessel injuries and excessive blood loss.
For those complex dumbbell schwannomas, if the osseous outlet is not big enough to resect the tumor in one piece via one incision, it is recommended to resect the tumor in the sacrum via the posterior incision first, while the tumor out of the sacrum should be well protected with gauze.
For total sacrectomy, to free the anterior surface of the first two sacral vertebrae, because their complete resection involves considerable difficulty, S1-S3 nerve roots are cut off ventrally and the accompanying arteries and veins should be ligated. There are some arteries and veins on the surface of the sacroiliac joint, going up from below. These vessels should be ligated as well to avoid uncontrolled bleeding when performing the osteotomy of sacrum posteriorly. It is not easy to disarticulate the sacroiliac joint. So it is recommended that the ventral sacroiliac osteotomy is performed 1.5 cm laterally away from the joint. A deep groove is made with high-speed burr in the ventral sacrum. After the dorsal cortex of the sacrum is broken, the sacrum is divided finally and the tumor is removed en bloc. It is essential to protect the gluteal vessels and the sciatic nerve while working in the greater sciatic notch.
If there are dense adhesions between the rectum and the anterior surface of the sacrum, the rectum should be resected with the sacrum.
Posterior Approach
The posterior incision starts from the lumbar spinous process and extends to 3 cm above the coccyx. However, the incision could be modified as a transversely placed H or Y. In the presence of a previous open biopsy, an elliptical incision should be made to get the entire biopsy track resected.
The incision is carried down to the deep fascia, and then the flaps are raised beyond the posterior superior iliac spine.
The fibers of the gluteus maximus are divided along the sacral edge below S3 and the lumbodorsal fascia above S3.
The lumbodorsal fascia is longitudinally open and a transversal incision is done at S3 level to expose and push the erector spinae muscles laterally. After the soft tissue is removed from the surface of the coccyx, the coccyx is exposed.
Sacral Osteotomy
The sacrum is marked with electrotome by measuring the distance between the coccyx and the preoperatively planned sacral osteotomy level (TECH FIG 1A,B). The gluteus maximus muscles are cut off 1 cm away from the insertion in the sacrum (TECH FIG 1C,D). The vessels in the gluteus muscles should be ligated carefully.
If the erector spinae muscles are not involved, they are detached from the insertions in the sacrum and pulled proximally. However, if they are involved, they are cut at the level of the sacral resection level, not the insertions.
After the ligaments are cut off from the ventral and bilateral aspects of the coccyx (TECH FIG 1E,F), some yellow adipose tissue is present in front of the sacrum.
By pushing the adipose tissue anteriorly, some space is saved to cut the insertions of the pelvic floor muscle in the sacrum.
Then the sacrotuberous ligament can be touched anterolateral to the sacrum and cut off subsequently. The sacrospinous ligament can be touched a little upper, accompanied by some vessels from the front. The vessels should be ligated when cutting off the sacrospinous ligament.
Then the piriformis are exposed. Only some of the piriformis can be cut off because some of the muscles are hidden behind the sacroiliac joint (TECH FIG 1G,H). The sacroiliac ligaments are cut off until the lower rim of the sacroiliac joint.
Some wet gauzes are applied in the presacral space to bluntly dissect the pseudocapsule of the tumor from the rectum.
Following division of the anococcygeal raphe, gentle, blunt finger dissection is performed for a short distance on the anterior surface of the bowel until the level of the transabdominal dissection is reached.
After the dissection is finished, wet gauze pads are used to protect the viscera.
The electrotome is used to expose the back aspect of the sacrum. After the sacral osteotomy level is confirmed, the dorsal sacral nerves below the osteotomy level are divided.
It is important to save the preserved nerves above the osteotomy level and ligate the vessels that are accompanying the nerves.
The posterior foramen is enlarged by removing some of the upper and lower bone around the foramen with varied sizes of maxillary punch cutting forceps. Then the nerve roots and the dura are clearly exposed. The right upper nerve root is anterolateral to the present nerve root, and the right lower nerve root locates inside the present nerve and outside the dura.
The dural sac is cut off and ligated caudally at this level as well as the lower nerve roots (TECH FIG 1I-L).
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Through the open window of the posterior foramen, the anterior foramen could be identified ventrally. One
nerve dissector is placed between the anterior foramen and the sacral nerve so the lateral sacrum is safely removed horizontally until the level of ilium.
The osteotomy is done from the bottom up in the ilium side of the sacroiliac joint to meet the previous osteotomy.
At this point, only the sacrum body is still connected. Two nerve dissectors are placed between the anterior foramen and the sacral nerve.
The anterior cortex of the sacrum is exposed by removing the cancellous bone with small curette. Then it is broken by an osteotome very carefully (TECH FIG 1M,N).
It is essential not to cut through the cortex of the sacrum to avoid unnecessary bleeding of the anterior soft tissue.
The anterior soft tissue is detached and ligated with hemostatic forceps while pulling the resected but still connected sacrum caudally. The insertion of the rectal ligament in the ventral sacrum is cut off after turning the sacrum over.
The sacral nerves below the osteotomy level are resected in front of the anterior foramen.
However, it is encouraged to anastomose the sacral nerves above S3 from the anterior foramen to the nerve ends at the osteotomy level. Nerve functions are expected to recover in a way.
Then the sacrum with tumor is removed en bloc (TECH FIG 1O,P).
Wound Closure
After meticulous hemostasis, the wound is then irrigated and two closed-system drainages are used. The erector spinae muscles and gluteus maximus are sutured together.
Finally, the incisions are closed in a routine fashion.
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TECH FIG 1 • A,B. If there is no navigation system available, the sacral osteotomy level is suggested to be marked with an electrotome before further procedures are taken. C,D. The gluteus maximus muscles are cut off 1 cm away from the insertion in the sacrum. The biopsy track should be resected together with the tumor. (continued)
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TECH FIG 1 • (continued) E,F. The ligaments connecting the coccyx and others are cut off ventrally and bilaterally. G,H. Some of the piriformis are exposed and subsequently divided. I,J. The dural sac should be cut off and ligated carefully to avoid unnecessary leakage of cerebrospinal fluid. (continued)
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TECH FIG 1 • (continued) K,L. The root nerves should be well protected when ligating the dural sac and cutting the sacrum. M,N. The anterior cortex of the sacrum is very carefully broken by an osteotome. Potential excessive bleeding is due to vessels in the soft tissues of the anterior surface of the sacrum. O,P. After the sacrum with tumor was removed, the saved sacral nerves and some anterior yellow presacral tissues were clearly seen.
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Computer-Assisted Navigation in Sacral Tumor Resection
The posterior incision starts from L5 and extends to the coccyx (TECH FIG 2A). The erector spinae muscles and the gluteus maximus muscles are adequately exposed laterally to the sacroiliac joint.
The patient tracker is placed relatively far away from the tumor (ie, the ilium, the proximal spinal process). It emits infrared light, from which the navigation system determines where the tumor and the surrounding osseous anatomic structures are (TECH FIG 2B-D).
Involvement of the erector spinae muscles and gluteus maximus is evaluated on preoperative imaging.
If no, the image-to-patient registration could be pointbased (sometimes surface-based). After raising the
flap of erector spinae muscles and the gluteus maximus muscles, the spinal process and vertebral are exposed, which serve as the anatomic landmarks for registration. Surgeons are required to specify the positions of the paired points and feed this information into the system for calculation of the transformation matrix. After registration, it is important to verify the accuracy of registration by placing a navigator tool over the exposed topographic landmarks.
If yes, the image-to-patient registration would be Iso-C based. The erector spinae muscles and gluteus maximus are cut off 1 to 2 cm away from the soft tissue mass. So those anatomic landmarks used in point registration are not exposed. Images were acquired by Iso-C three-dimensional (3-D) C-arm with automated orbital rotation of 190 degrees. The images were reconstructed in processor unit of Iso-C and transferred automatically to computer workstation. Preoperative CT/MRI in Digital Imaging and Communications in Medicine (DICOM) format is imported to the navigation system. Fusion of CT/MRI with Iso-C is performed using “surface matching image correlation,” and this automatically registers the bone with MRI/CT (TECH FIG 2E). The fused images are then ready for 3-D navigation procedures.
The sacral osteotomy is guided by the computer-assisted navigation system. After the en bloc resection, the navigation system could be used to verify if the surgical margin is adequate by placing a navigator tool over the remaining sacrum (TECH FIG 2F).
Then, after meticulous hemostasis, the wound is irrigated and closed-system drainages were used. The incision is closed in a routine fashion.
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TECH FIG 2 • A. The Stryker computer navigation system. The patient was laterally positioned to facilitate the navigation process. The surgeon knows exactly where the tumor and the surrounding structures are via the system. Preoperative CT (B) shows the bone destructions very well and MRI (C) demonstrates the involved soft tissues. D. The good points of both CT and MRI are united when the imaging fusion technique is applied. (continued)
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TECH FIG 2 • (continued) E. Preoperative surgical plan with detailed sacral resection design. F. After the tumor was removed, the navigation was used to verify the accuracy of the resection. In part B to D, the blue arrow indicates the bone margin of the tumor while the red arrow indicates the soft tissue margin of the tumor.
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Total Sacrectomy and Screw-Rod System Reconstruction
Surgical plan is well planned based on CT and MRI, and the surgery is practiced preoperatively on sawbones (TECH FIG 3A-D).
Navigation system is encouraged to facilitate the accurate resection and reconstruction as well (TECH FIG 3E,F).
The patient is in the prone position with the posterior approach. The posterior incision extends from L3 to the coccyx. The posterior iliac crests, greater sciatic foramina, and sciatic nerves are exposed bilaterally as well as the L3-L5 spinal processes, facet joints, and transverse processes. After L5 laminectomy is done, the sacral nerve roots are then cut off, and the dural sac is ligated caudally.
The sacroiliac osteotomy is performed 1.5 cm laterally away from the sacroiliac joint. Then the entire
sacrum with the tumor is removed en bloc as described previously (TECH FIG 3G).
Two vertical L-shaped rods are positioned bilaterally in a manner allowing fixation to the L4-L5 pedicles on each side (TECH FIG 3H). One cross-connecting rod is used to secure the vertical rods to each other.
Two screws in each side are placed to fix the iliac bones to each other and thereby prevent axial rotation of the lumboiliac union (TECH FIG 3I-L).2
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TECH FIG 3 • A. Preoperative CT scan shows S5 involvement by malignant tumors. B. MRI shows the malignant tumor involvements more clearly. Total sacrectomy was planned. C. The posterior view of the sacrum shows the bone destruction in the sacrum and the planned screw in S4-S5. D. Two screws were preoperatively planned to nail the iliac bones to strengthen the sacroiliac joint stability. (continued)
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TECH FIG 3 • (continued) E. Navigation was used to design the resection of the tumor. F. Navigation was used to nail the screw in the spine as well. G. After the tumor was removed, the remaining S1 nerve could be clearly seen. H. How the screw and rod was used to construct the sacroiliac joint stability. AP (I) and lateral
(J) views of the resected entire sacrum with tumors. (continued)
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TECH FIG 3 • (continued) AP (K) and lateral (L) postoperative radiographs.
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PEARLS AND PITFALLS
Preoperative ▪ Careful review of preoperative imaging studies, well-planned surgical design, and adequate preoperative preparations are crucial to the success of surgery.
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Embolization within 24 hours before surgery is significant in minimizing blood loss during surgery. Selective embolization and avoiding embolization of superior gluteal artery are helpful to prevent flap necrosis.
Intraoperative ▪ The posterior midline approach is the most common approach for sacral tumor resection. If the tumor is pretty large, two transversal incisions could be added to formulate a transversely placed H incision. The flap should be raised deep into the deep fascia to reduce risks of necrosis.
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If the tumor is well circumscribed in the sacrum and the erector spinae muscles are not involved, the cavity after tumor resection may be filled with these muscles.
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The insertions of the gluteus maximus, the piriformis, the sacrotuberous ligament, and the sacrospinous ligament are vulnerable to be involved by tumors. It is recommended to cut those structures at least 1 cm away from the insertions to ensure adequate surgical margin and thereby reduce the risks of local recurrences.
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There is a layer of loose tissue in the presacral area, from which the rectum could be easily bluntly detached to avoid unnecessary injury.
Postoperative ▪ Efficient drains are securely kept in place until 24-hour drainage is less than 20 mL because a large hematoma may develop in the cavity and result in severe infections. The position of lying down for long periods of time should be avoided to prevent flap necrosis.
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Vital signs as well as drainage should be closely monitored postoperatively.
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A heavy blood loss should be considered when one or more of the following happen: rapidly increased drainage during a short period of time, abdominal distension with dull percussion sounds, symptoms of shock, and progressively decreased hemoglobin.
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Fluid therapy, blood transfusion, temporary clamping of the drainage tube, emergency angiography, and embolization are possible managements for blood loss. Surgical exploration is not recommended due to its high risks for further bleeding and infections.
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The cavity easily gets infected. Skin necrosis and wound infections should be closely monitored. Early débridement and closure are usually associated with a better outcome.
POSTOPERATIVE CARE
Regular repositioning is required to prevent flap necrosis if the patient is supine postoperatively. Lateral position should be applied once the patient has stable vital signs.
Patients should stay in the ICU to get the vital signs and the drainage closely monitored. Special attention
should be given to the observation of possible heavy postoperative bleeding.
Continuous perioperative intravenous antibiotics are continued until the drainage is less than 20 mL and the tubes are removed.
The patient may begin ambulation 10 to 14 days postoperatively if no reconstruction surgery is performed. However,
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progressive ambulation is not encouraged until 4 to 6 weeks postoperatively if reconstruction surgery is performed.
All postoperative patients should have a sacral radiograph and CT scan as the baseline for the possible followup comparisons (FIG 8).
Serial evaluations of the specimen are used to verify whether the surgical resection matches the preoperative design. (FIG 9)
OUTCOMES
Todd et al4 retrospectively analyzed the bowel and bladder function in 53 patients with major sacral resection.
In patients who had bilateral S2-S5 nerve roots sacrificed, all had abnormal bowel and bladder function.
In patients who had bilateral S3-S5 resection, normal bowel and bladder function was retained in 40% and 25%, respectively.
In patients who had bilateral S4-S5 resection, with preservation of the S3 nerves bilaterally, normal bowel and bladder function was retained in 100% and 69%, respectively.
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FIG 8 • Postoperative anteroposterior (AP) (A) and lateral (B) radiograph and coronal (C) and sagittal
(D) CT scans.
In patients who had asymmetric sacral resections, with preservation of at least one S3 nerve root, normal bowel and bladder function was retained in 67% and 60%, respectively.
In patients who had unilateral sacrectomy, in whom the contralateral sacral nerves were preserved, normal bowel and bladder function was retained in 87% and 89%, respectively.
COMPLICATIONS
Intraoperative excessive blood loss is the most common complication. It is believed that angiography and subsequent embolization could significantly reduce the intraoperative blood loss, especially for those sacral tumors with high risks of mortality (ie, high-level or pretty large).
Infection is another significant complication, and it is devastating when any implants are placed. Use of antibiotics by combinations during the perioperative phase is extremely important. Preoperative bowel preparation is also necessary.
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FIG 9 • A. The formalin-fixed specimen was shown in four pictures. The posterior view of the sacrum showed there is no tumor exposed posteriorly. B. The anterior view of the sacrum showed there is no tumor exposed anteriorly. C. The sagittal view of the split specimen showed the resection of the sacrum was well performed. D. The axial view of the specimen showed the margin of the resection was macroscopically negative.
Wound problems including infections, skin or muscle necrosis, nonhealing wounds, and wounds dehiscence are very challenging complications. The large cavity after resection, lacking muscles covering the wound, and possible hematoma in the wound are known risk factors of infections.
Rectal injury during sacral tumor resection has been reported in the literature. The reasons could be either direct damage to the rectum or compromised blood supplies to the rectum. The rectal necrosis usually aggravates the infections.
Nerve injury is a common complication, especially when the nerve is involved or the tumor has locally recurred. Special attention should be given to the sciatic nerve when the tumor is very large with extensive soft tissue involvement.
The leakage of cerebrospinal fluid is a rare complication. No ligation after cutting off the dural sac and
being hard to ligate it in recurred high-level sacral tumors are the main two possible reasons, which should
be clinically paid more attention to.
REFERENCES
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Fourney DR, Gokaslan ZL. Current management of sacral chordoma. Neurosurg Focus 2003;15(2):1-5.
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Gokaslan ZL, Romsdahl MM, Kroll SS, et al. Total sacrectomy and Galveston L-rod reconstruction for malignant neoplasms. Technical note. J Neurosurg 1997;87(5):781-787.
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Hugate RR, Dickey ID, Phimolsarnti R, et al. Mechanical effects of partial sacrectomy: when is reconstruction necessary? Clin Orthop Relat Res 2006;450:82-88.
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Todd LT, Yaszemski MJ, Currier BL, et al. Bowel and bladder function after major sacral resection. Clin Orthop Relat Res 2002; (397):36.