Surgical Resection of Sacral Tumors

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Chapter 193 Surgical Resection of Sacral Tumors

Ziya L. Gokaslan, Wesley Hsu

Tumors involving the sacral spine are rare lesions that can lead to significant morbidity and mortality. Symptoms may be minimal during the early stages of disease, and the clinical evaluation of these lesions is often delayed. Thus, sacral tumors are often far advanced at the time of diagnosis. Clinical management is dictated by the tumor type, the location of the lesion, and the tumor’s relationship to adjacent neural, vascular, and pelvic structures. The overall medical status of the patient must also be considered, particularly in patients with metastatic disease.

Primary tumors of the sacrum, including chordomas, chondrosarcomas, and giant cell tumors, are usually poorly responsive to radiation and chemotherapy. Surgical resection of these lesions can help improve the efficacy of adjuvant therapies or even lead to long-term recurrence-free survival. In contrast to primary tumors, the majority of metastatic lesions are responsive to radiation and chemotherapy. However, advanced metastatic disease can lead to acute cauda equina syndrome or sacral insufficiency, thus necessitating surgical intervention.

Resection of sacral lesions is often technically challenging and requires a multidisciplinary approach to maximize clinical outcomes. Collaboration among neurosurgery, general surgery, and plastic surgery as well as medical and radiation oncology is critical when treating advanced sacral oncologic disease. Knowledge of the complex anatomy in the sacropelvic region is critical. Care must be made to balance the potential benefits of surgical resection with the possibility of significant morbidity during the course of surgical treatment.

The goal of this chapter is to review the critical anatomy of the sacropelvic region, discuss the clinical presentation and evaluation of patients with sacral tumors, briefly review common tumors that involve the sacrum, and discuss in depth the variety of surgical approaches available to resect tumors of the sacrum.

Anatomy

Osseous and Ligamentous Structures

The adult sacrum consists of five fused sacral vertebrae. At birth, each vertebral body is separated by an intervertebral disc. The two caudal bodies fuse at approximately the 18th year of life, and the process of fusion continues rostrally until the S1–2 interspace finally fuses by 30 years of age. The development of fused vertebrae is dependent on normal weight bearing.

The sacrum is wedge shaped, and the broad base of S1 forms the posterior segment of the pelvic ring. The upper sacral vertebrae articulate with the ilium bilaterally. The ventral sacrum is concave and contains the ventral sacral foramina of the S1–4 nerve roots. Exiting the foramina are the paired sacral nerves and associated vascular elements. The transverse prominences between each pair of foramina represent the area where the intervertebral disc was once located.

The pars lateralis (lateral mass) is the area lateral to the ventral foramina. The lateral surfaces of the upper two or three sacral vertebrae form an ear-shaped “auricular” surface, which articulates with the ilium on each side. Ventrally, the lateral masses are marked by neural grooves that run laterally from each of the foramina. The large lateral masses of S1 are known as the alae. On the anterior aspect of each ala is a rounded bony groove formed by the lumbosacral trunk.

The dorsal surface of the sacrum is convex and has an irregular surface that includes median, intermediate, and lateral sacral crests representing the fused spinous, articular, and transverse processes, respectively. The shallow grooves between the median and intermediate crests are formed by fused laminae. The dorsal rami of the upper four sacral nerves and associated vascular structures pass through the four pairs of dorsal sacral foramina, located between the intermediate and lateral sacral crests. The dorsal sacral foramina are much smaller than the corresponding ventral sacral foramina. The laminae of the fifth (and on occasion the fourth) vertebra fail to fuse in the midline and form the sacral hiatus, which is the caudal opening of the sacral canal. The sacral cornua, remnants of the inferior articular process, lie on each side of the sacral hiatus.

Because the lumbosacral and sacroiliac joints transmit the entire weight of the body to the hip bones and lower limbs, these joints and their supporting ligaments must be very strong. The strong dorsal ligamentous complex includes the interosseous ligaments and the dorsal sacroiliac ligaments. The very stout interosseous ligaments connect the sacral tuberosities to the overhanging bone of the iliac tuberosities and represent the single strongest ligaments binding the sacrum to the ilium. The dorsal sacroiliac ligaments are divided into deep (short) and superficial (long) parts. The deeper ligaments connect the sacral and ilial tuberosities and are composed of horizontally oriented fibers; the more superficial ligaments are oriented vertically and stretch from the posterior superior iliac spine to the tubercles of the lateral sacral crest. The caudal portions of the superficial dorsal sacroiliac ligaments blend with the sacrotuberous ligaments.

The ventral ligamentous complex includes the ventral sacroiliac ligaments and the lumbosacral ligaments. The ventral sacroiliac ligament is a weak fibrous band that attaches to the base and lateral part of the sacrum and to the medial margin of the auricular surface of the ilium.

Three sets of accessory ligaments—the sacrospinous, sacrotuberous, and iliolumbar ligaments—also function to strengthen the pelvic girdle. The iliolumbar ligament originates on the transverse process of L5 and courses caudally and laterally to insert on the ilium. Some fibers stretch ventrally to merge with the ventral sacroiliac ligament as the lumbosacral ligament. The sacrospinous ligament connects the lateral and anterolateral surfaces of the sacrum and coccyx with the ischial spine. This ligament divides the sciatic notch into greater and lesser sciatic foramina. Finally, the sacrotuberous ligament, an extensive structure, originates broadly from the posterior superior iliac spine and the dorsal and lateral aspects of the sacrum and coccyx to form a dense narrow fibrous band that inserts on the ischial tuberosity.

Vascular Anatomy

The abdominal aorta bifurcates at the L4 level. The small median or middle sacral artery arises from the posterior surface of the abdominal aorta close to the bifurcation and descends vertically along the pelvic surface of the sacrum. It gives rise to several small parietal branches that anastomose with the lateral sacral arteries and to small visceral branches that anastomose with the superior and middle rectal arteries.

The aorta divides into the common iliac arteries, which travel laterally and inferiorly. At approximately the L5–S1 disc space, the common iliac arteries divide into the external and internal iliac arteries. The ureter crosses the external iliac artery anteriorly. The internal iliac artery is separated from the sacroiliac joint by the internal iliac vein and the lumbosacral trunk.

The iliolumbar artery can arise from the common iliac artery, although it more commonly is the first branch of the internal iliac artery. This vessel runs superomedially, passing anterior to the sacroiliac joint and posterior to the psoas muscle. It later turns laterally and upward to divide in the region of the iliac fossa. The lateral sacral artery is usually the second branch of the internal iliac artery, although it can originate from the superior gluteal artery. These vessels, usually a superior one and an inferior one, sometimes arise from a common trunk. They pass medially and descend downward anterior to the sacral ventral rami, giving branches that enter the ventral sacral foramina to supply the spinal meninges and the roots of the sacral nerves. Some branches pass from the sacral canal through the dorsal foramina to supply the muscles and skin overlying the sacrum. Most tumors arising from the sacrum or presacral space, as well as some intraspinal masses, derive at least a part of their blood supply from the medial and lateral sacral arteries. Enlargement, displacement, or encasement of these vessels may be seen on angiography.

The next two branches of the internal iliac artery are the superior and inferior gluteal arteries. The superior gluteal is a large artery that passes anteriorly across the lumbosacral trunk as the trunk passes over the ala. It then turns posteriorly between the lumbosacral trunk and the ventral ramus of the first sacral nerve to leave the pelvis through the superior part of the greater sciatic foramen, superior to the piriformis muscle. The inferior gluteal artery passes posteriorly to pierce the sacral plexus more inferiorly (most often between S2 and S3) and exits the pelvis through the inferior part of the greater sciatic foramen, inferior to the piriformis muscle.

The venous anatomy of the region generally parallels that of the arterial anatomy, but it is more variable. There are several important features of the venous anatomy to note. First, the vena cava lies to the right of the aorta at the bifurcation of the common iliac vessels. The right common iliac vein passes posterior to the common iliac artery, and it is therefore shorter than the left common iliac vein. Second, the middle sacral vein, which is occasionally doubled, drains into the left common iliac vein rather than directly into the inferior vena cava. Finally, the iliolumbar veins drain into the common iliac veins rather than into the internal iliac veins.

Neural Anatomy

The thecal sac ends blindly at the S2 level. The lower sacral and coccygeal nerves emerge from the sac, as does the extradural portion of the filum terminale. The upper four roots exit the sacrum through the paired ventral and dorsal sacral foramina. The fifth sacral roots, the coccygeal roots, and the filum exit the sacrum caudally through the sacral hiatus. The filum terminale extends to its point of fusion with the periosteum of the first coccygeal segment.

The sacral plexus is formed by the ventral rami of six roots: L4 through S3 and the upper part of S4. The lumbosacral trunk (the conjoined L4–5 roots) crosses the anterior aspect of the ala of the sacrum, descends obliquely in front of the sacroiliac joint, and enters the pelvis deep to the parietal pelvic fascia. It crosses the superior gluteal vessels and joins the first sacral root. The sacral plexus is located on the anterior surface of the piriformis muscle, deep to the parietal (Waldeyer’s) fascia. Except for the nerves to the piriformis muscle, the perforating cutaneous nerves, and the nerves to the pelvic diaphragm, essentially all branches of the sacral plexus leave the pelvis through the greater sciatic foramen.

The most important derivatives of the sacral plexus are the sciatic and pudendal nerves. The latter is unique in exiting the greater sciatic foramen only to reenter the lesser sciatic foramen by hooking around the sacrospinous ligament. It supplies the muscles of the perineum, including the external anal sphincter, and provides sensory information to the external genitalia.

The coccygeal plexus is derived from the ventral rami of S4 and S5 as well as the coccygeal roots. It lies on the pelvic surface of the coccygeus muscle. It innervates the coccygeus muscle and provides some perianal sensation.

Both the sympathetic and parasympathetic components of the autonomic nervous system have an intimate relationship with the sacrum. The sacral sympathetic trunk, continuous with the lumbar sympathetic trunk, descends against the ventral surface of the sacrum, converging in front of the coccyx to form the unpaired ganglion impar. Three or four sacral trunk ganglionic enlargements are found on each side of the midline, just medial to the ventral sacral foramina. No white rami communicantes are present in this region; however, the postsynaptic gray rami communicantes from each ganglion join the corresponding sacral or coccygeal nerves for distribution to sweat glands, blood vessels, and erector pilori muscles. In addition, the sacral sympathetic trunks provide fine branches to the superior hypogastric plexus. The superior hypogastric plexus is the caudal continuation of the periaortic sympathetic plexus; it lies on the anterior surface of the fifth lumbar vertebra and upper sacrum in the retroperitoneal tissue. Fibers of the superior hypogastric plexus diverge into right and left hypogastric nerves opposite the first sacral vertebra. The term hypogastric nerve may be a misnomer, because the structure is really a narrow plexus of fibers. The hypogastric nerves represent the principal sympathetic inputs to the inferior hypogastric plexus.

The parasympathetic contributions to the pelvic plexi arise from the ventral S2 to S4 nerve roots. These preganglionic fibers form the pelvic splanchnic nerves (nervi erigentes). The parasympathetic system provides motor innervation to the detrusor muscle of the bladder and is primarily responsible for the vascular reflexes that sustain erectile function. The sympathetic system plays less of a role in normal voiding reflexes but is important for male fertility by promoting timely transport of spermatozoa from the testes to the seminal vesicles and by coordinating reflexes responsible for ejaculation.

Diagnosis

Clinical Presentation

Sacral tumors are rare and difficult to diagnose at an early stage.1 The major reasons for this delay include the unique capacity of the osseous sacrum and sacral canal to allow neoplastic expansion without causing significant symptoms and the often nonspecific nature of complaints when they do arise. Tumors that originate within the sacral canal can erode or invade the walls of the sacrum and/or expand cephalad within the spinal canal. Tumor can also enter the pelvis via the ventral sacral foramina. A slow-growing, regionally expansive neoplasm can attain a large size without causing symptoms early in the course of the illness. Aggressive, rapidly growing tumors are more likely to cause mechanical instability and/or neurologic compromise earlier during the disease course.

The earliest presenting symptom in patients with sacral tumors is pain located in the lower back or sacrococcygeal region.1–3 Referred pain to the leg or buttock can occur secondary to irritation of the first sacral root or iliolumbar trunk.3 The early presentation of sacral lesions is therefore very similar to that of lumbar spondylosis. By the time a sacral lesion is diagnosed, some patients have been treated and occasionally even operated on for suspected lumbar intervertebral disc pathology.

Abnormalities on plain sacral radiographs may be missed, and routine lumbar myelography, computed tomography (CT), and magnetic resonance imaging (MRI) studies can fail to visualize the sacrum below the S2 level. The true diagnosis is commonly realized late in the course of illness, when bladder or bowel function have been compromised, or when a large presacral mass is noted on rectal or gynecologic examination.

Radiologic Evaluation

A sacral tumor can be easily overlooked on standard radiographs. The curved shape of the sacrum, its position within the pelvic girdle, and overlying bowel gas are common sources of obscuration. Destructive changes must be advanced before they become evident on plain radiographs.4 Adequate imaging should display the entire sacrum and coccyx on lateral views, and the sacrum should be visualized en face on anteroposterior views. A malignant process is suggested when lytic lesions without sharply defined borders are seen. Well-defined sclerotic margins, reflecting reactive changes in the surrounding bone, imply the presence of a benign or chronic process.

CT and MRI more readily allow the detection, characterization, and staging of sacral tumors.4,5 CT has the advantage of providing excellent bony detail and showing tumor matrix calcification. CT is also useful to image the abdomen for evidence of visceral involvement. Major advantages of MRI studies include the detailed depiction of associated soft tissue masses and the ability to assess the anatomy in multiple planes. The rostral extent of sacral involvement, which is particularly critical to surgical planning, is best appreciated on a midsagittal view.

The radionucleotide bone scan is a sensitive but nonspecific indicator of bone destruction that is most useful as part of a systemic workup to rule out widespread bony metastases during the preoperative staging of these patients. Purely osteolytic lesions, such as myeloma, may not be well defined on bone scan. Obscuration of sacral lesions by the accumulation of radioactive material in the bladder can result in falsely negative study results.

In addition to the bone scan, CT scans of the chest, abdomen, and pelvis are warranted to rule out metastatic pathology. Intravenous pyelography and/or barium enema may be indicated in evaluating sacral tumors with significant pelvic invasion as well as for colorectal tumors that invade the sacrum.6 Angiography is useful in defining the vascularity of sacral tumors and for preoperative tumor embolization, especially in the case of highly vascular lesions such as giant cell tumor or aneurysmal bone cyst.7,8

Biopsy

The differential diagnosis of sacral tumors is extensive. Although patient demographics, clinical presentation, and radiographic imaging might suggest a differential diagnosis, a biopsy should be performed in virtually all cases. In a patient with significant comorbid illness who is not considered a candidate for a major surgical resection, a biopsy may still be warranted in order to plan radiotherapy or chemotherapy.

The percutaneous CT-guided biopsy involves minimal risk and is currently the method of choice. The site of entry and the trajectory of the needle should be carefully selected so that they can easily be included within the margins of any subsequent resection. If possible, the puncture site should be located in the midline posteriorly. It may be worthwhile to introduce a small droplet of sterile permanent ink into the needle tract to tattoo the skin for later identification.

A transrectal biopsy should be avoided, because the otherwise uninvolved rectum can become seeded with tumor cells, necessitating later resection. Additionally, following transrectal biopsy, the tumor bed can be infected.

Pathology

Sacral tumors are categorized as those that originate from the neural elements or their supporting tissues, those arising from bone, and those that metastasize from distal sites or are the result of direct invasion from adjacent pelvic structures. The most common sacral tumors are metastatic, and the most common primary sacral tumor is chordoma.2 Some non-neoplastic entities, including developmental cysts and inflammatory conditions, mimic sacral tumors on imaging studies. A broad differential diagnosis of the various lesions encountered in this area is provided in Table 193-1.

TABLE 193-1 Differential Diagnosis of Sacral and Presacral Lesions

Congenital Lesions
Posterior sacral meningocele, meningomyelocele, and lipomyelomeningocele
Developmental cysts
Dermoid and epidermoid cysts
Retrorectal tailgut cysts
Enteric duplication cysts
Anterior sacral meningocele
Lateral meningocele
Occult intrasacral meningocele
Perineural (Tarlov’s) cysts
Tumors
Primitive Neuroectodermal Tumors
Teratoma
Hamartoma
Chordoma
Inflammatory Lesions
Osteomyelitis
Abscess (pelvic abscess, perirectal abscess)
Neurogenic Lesions
Schwannoma and neurofibroma
Ependymoma
Ganglioneuroma
Neuroblastoma
Osseous Lesions
Bone island
Osteoid osteoma and osteoblastoma
Osteochondroma
Hemangioma
Aneurysmal bone cyst
Giant cell tumor
Chondrosarcoma
Osteosarcoma
Ewing’s sarcoma
Paget’s disease (monostotic)
Metastatic Lesions
Hematogenous spread (lung, breast, prostate, kidney, lymphoma)
Locally invasive lesions (colorectal and gynecologic malignancies, sarcoma)
Miscellaneous Lesions
Carcinoid tumor
Lymphoma
Solitary plasmacytoma, multiple myeloma
Meningioma
Hemangiopericytoma

Congenital Tumors

Sacrococcygeal Teratoma

A teratoma is a lesion containing tissue from all three germ layers, represented by either well-differentiated or immature elements. Skin, teeth, central nervous system tissue, and respiratory and alimentary mucosa may be found within these tumors. Sacrococcygeal teratomas are the most common sacral tumor in neonates. In contrast, these tumors are rare in adults.9 They develop during intrauterine growth and can grow large enough to cause dystocia.10 The diagnosis is often made on prenatal ultrasonography.11 After birth they manifest as an exophytic mass located between the anus and coccyx, covered by normal skin. Presacral and sometimes combined pre- and postsacral (dumbbell-shaped) lesions also occur.

Chordoma

Chordoma is the most common primary bone tumor of the sacrum.12 Sacral chordomas occur almost twice as often in men compared with women and are uncommon in persons younger than 40 years. The most common presenting symptom is pain in the lower back or sciatic region.3 Chordomas can reach a very large size before constipation (from rectal compression) or lower extremity paresis (due to sacral plexus involvement) occurs.

Chordomas are considered congenital because they are thought to arise from notochordal remnants. Chordoma is characterized microscopically by the appearance of vacuolated “physaliferous” cells. The midline location of these tumors also relates to this proposed etiology.13

Chordomas are typically slow growing but locally aggressive. Significant extracompartmental growth is often seen by the time of diagnosis. Most sacral chordomas manifest as surgical stage IB with anterior extension into the pelvis.14 The tumor often displaces but does not invade the rectum, because the tough periosteum and presacral fascia resist the transgression of disease. Metastasis is usually a late event.

The usual CT appearance consists of lytic bone destruction in addition to a disproportionately large soft tissue mass. Calcification is present in 30% to 70% of cases.5 Unlike most bone tumors, chordomas can show reduced uptake or normal distribution of isotope on bone scan.

En bloc excision is the treatment of choice for sacral chordomas.2,12,13 The extent of surgical resection has been found to play a major role in determining the length of disease-free survival.13 Although a distinct capsule is often seen within the soft tissues, a radical wide posterior margin of the gluteal muscles should be employed to reduce the risk for local recurrence.15 The margins of chordoma within bone are often indistinct. Surgical resection should extend at least one sacral segment beyond the area of gross disease.2

The value of radiotherapy as primary or adjuvant treatment for chordoma has been debated.12 Supplementary radiotherapy may be a useful adjunct to surgical care, but it is not sufficient as stand-alone therapy. In a clinical series spanning 40 years, York and colleagues2 reported that the addition of radiation therapy significantly prolonged the disease-free interval for patients undergoing subtotal resection (2.12 years versus 8 months). Others have suggested that radiotherapy is of limited value in most cases.13

Currently, chemotherapy does not play a role for the treatment of chordomas, although the use of imatinib mesylate is being investigated.16

Neurogenic Tumors

Schwannoma and Neurofibroma

Sacral schwannomas are much more common than neurofibromas. They grow within the sacral canal and only rarely expand through the anterior sacral foramina into the presacral space.17,18 A complete resection of these benign tumors is potentially curative because, with the exception of plexiform neurofibromas, they do not infiltrate beyond their capsular envelope. The surgical approach depends on the size and location of the tumor, especially the degree of intraspinal and presacral extension. The majority of lesions coming to neurosurgical attention are largely confined to the sacral canal and can be resected completely using a posterior approach. This approach allows direct visualization of the relationship between the sacral nerve roots and the tumor. If there is a small presacral component, limited access to this region may be obtained by transforaminal resection. Tumors with a large presacral component should often be removed through an anterior transabdominal approach. Giant intrasacral schwannomas have been described for which radical sacral resection was performed. 17,18

Ependymoma

Sacral ependymomas are most commonly the benign myxopapillary type. They arise from ependymal cell clusters within the terminal filum and expand the sacral canal.19 Rare extradural sacrococcygeal ependymomas have been reported, including subcutaneous, presacral, and intrasacral varieties.20

Patients with sacral region ependymomas typically present with pain in either a lower back or sciatic distribution. By the time of diagnosis, which averages 2 to 3 years after the onset of symptoms, many patients exhibit some form of cauda equina syndrome.3 As with other slow-growing sacral tumors that tend to be diagnosed at an advanced stage, ependymomas may be associated with extensive bony destruction and a large soft tissue mass.19

A complete en bloc resection is advisable in order to prevent local recurrence or cerebrospinal fluid dissemination. Intradural lesions can be resected completely via a posterior approach.20 Intraoperative somatosensory-evoked potentials are useful, because dissection of tumor from the roots of the cauda equina can be difficult. The approach to extradural lesions depends on tumor location. Radiotherapy may be useful in cases of subtotal removal or recurrence.

Ganglioneuroma

Ganglioneuromas are rare slow-growing tumors composed of sympathetic ganglion cells.21 They are thought to represent the benign counterpart of malignant neuroblastomas. Ganglioneuromas can arise anywhere from the base of the skull to the pelvis. Like neuroblastomas, most ganglioneuromas arise in the abdomen, predominantly from the adrenal gland. The small percentages of pelvic tumors likely arise from sacral extensions of the sympathetic chain. As tumor expands within the pelvis, it can extend through a sacral foramen into the epidural space, causing sacral nerve root compression. The treatment is complete surgical removal.

Primary Osseous Tumors

Less than 10% of all primary bone tumors occur in the spine, with the exception of osteoblastoma, which has a 40% incidence of vertebral involvement.22 The incidence of sacral involvement among osseous tumors varies considerably. Bone tumors are a histologically diverse group of neoplasms. Some lesions are of low biological activity, such as osteoid osteoma, osteoblastoma,22,23 and aneurysmal bone cyst.24 High-grade lesions include chondrosarcoma and osteosarcoma. Although giant cell tumors are histologically benign, they are locally invasive and have a high risk for recurrence.25

Aneurysmal Bone Cysts

Aneurysmal bone cysts are expanding lesions with blood-filled cavities separated by septa of trabecular bone or fibrous tissue containing osteoclast giant cells. The pathophysiology remains unclear, and there is much debate as to whether these lesions are neoplastic. Approximately 80% of cases occur in the first two decades of life. Although some lesions resolve spontaneously in time, the majority of these lesions exhibit variable growth rates over time.

There is much debate over the best treatment for spinal aneurysmal bone cysts. Among the treatment modalities, complete surgical excision of the lesion remains the most effective, with the lowest rate of recurrence.26,27 Alternatively, these lesions are often treated by intralesional curettage and bone grafting. The disadvantage of this technique is that it is often associated with greater blood loss as well as high recurrence rates ranging from 20% to 60%.28,29 Selective embolization has been shown to avoid excessive bleeding when used with surgery and has also proved to be an effective sole treatment in cases that are difficult to treat surgically. Several less-invasive methods have been studied for the treatment of aneurysmal bone cysts including particulate embolization, intralesional injection of alcoholic zein, radiotherapy alone,30 and radiotherapy combined with surgery.31 Radiotherapy can be used as an alternative or adjunct to surgery when aneurysmal bone cysts are located in sites where an adequate resection cannot be done without resulting in significant morbidity or poor cosmetic results.

Osteoid Osteoma and Osteoblastoma

Osteoid osteomas and osteoblastomas are bone-producing lesions that often occur in long bones but may also be found in the spine. Although these tumors have a predilection for posterior elements of the mobile spine, they tend to involve the body of the sacrum.22 These lesions are similar histologically to each other, containing osteoblasts that produce osteoid and woven bone. Osteoid osteomas are small, self-limited, and benign, whereas osteoblastomas are often larger, are more aggressive, and can become malignant.23

Osteoid osteomas and osteoblastomas are common causes of painful scoliosis in children and adolescents. The most common presenting symptom is neck or back pain that often responds to aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs). Chemotherapy has played a minimal role in the treatment of these lesions and has only been used in selected patients with recurrent aggressive lesions or in patients with surgically inaccessible lesions. Surgery becomes the primary treatment for osteoid osteoma and osteoblastoma as the pain becomes more severe and less responsive to medication. Complete resection is often curative for these lesions. Incomplete resections are more common in osteoblastomas than in osteoid osteomas because osteoblastomas are larger and more commonly involve extraosseous tissue. Osteoblastomas recur in 10% to 15% of cases,32 and the recurrence rate of osteoid osteomas is 4.5%.33

Giant Cell Tumor

Giant cell tumors of the spinal column have a predilection for the thoracolumbar and sacral regions. It is the second most common primary sacral tumor after chordoma. Patients with spinal involvement usually present in the third and forth decades of life. Giant cell tumors are believed to arise from mononuclear cells of macrophage origin. Histologically, they are multinucleated giant cells and macrophages that can contain areas resembling aneurismal bone cysts, and care should be taken when interpreting bone biopsy samples to avoid an erroneous diagnosis. Although they are histologically benign, approximately 5% to 10% of giant cell tumors undergo malignant degeneration and assume a more aggressive course.34

Clinical management of giant cell tumors is difficult given their high propensity for recurrence. En bloc resection with wide margins is the gold standard for treating these lesions.35 Unfortunately, these tumors often grow to a large size before initial diagnosis, and extension of the tumor into the spinal canal and adjacent soft tissues is not uncommon. Therefore, subtotal resection in concert with adjuvant chemotherapy, arterial embolization, and/or radiosurgery is the typical treatment when en bloc resection is not feasible.

Arterial embolization is a critical adjuvant therapy that can increase the safety of surgery as well as improve progression-free survival. Preoperative embolization is a useful tool that minimizes intraoperative blood loss during the resection of these highly vascularized tumors. Embolization may be especially useful to limit bleeding during intralesional resections. Interestingly, arterial embolization may also be useful as a primary treatment modality.8

Chondroma and Chondrosarcoma

Chondromas are cartilaginous tumors found primarily in the small bones of the hands and feet. These tumors are rarely found in the spine. They can be divided into enchondromas (originating from the medullary cavity) or periosteal chondromas (originating from the cortex). These lesions commonly manifest with local tenderness and/or a palpable mass when the tumor expands into surrounding tissue.

Complete surgical resection with negative margins is the primary treatment for chondromas. Less than 10% of patients experience tumor recurrence after complete resection.36 If incomplete resection is performed, residual tumor is at risk for sarcomatous degeneration. Because chondromas are radioresistant lesions, radiosurgery currently does not have a significant role in the treatment of these tumors.

Chondrosarcomas are slow-growing tumors that commonly manifest with focal pain or neurologic deficits. Although chondrosarcomas can be divided into multiple pathologic subgroups, the most important characteristic with respect to clinical outcome is the World Health Organization (WHO) grade. Grade I chondrosarcomas have a 90% 10-year survival rate compared to 30% to 40% for high-grade lesions.37

Regardless of WHO tumor grade, the gold standard for treating chondrosarcomas is gross total resection with negative margins. The literature suggests that en bloc resection is associated with long-term recurrence-free survival. En bloc resection can result in recurrence rates of 20% or less.38 In cases of tumor recurrence, repeat resection can lead to improved survival. There is no well-defined role for radiation or chemotherapy for these lesions.

Osteosarcoma

Osteosarcoma, the most common primary spine sarcoma, accounts for 3% to 15% of all primary spine tumors. Paget’s disease is a known risk factor for osteosarcoma, but less than 1% of patients with Paget’s disease develop malignant transformation. Distant metastases are often present at the time of diagnosis.

In a study of osteosarcoma, including 15 patients with sacral lesions,39

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