Sacral Tumors: Regional Challenges

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Chapter 114 Sacral Tumors

Regional Challenges

Tumors of the sacrum are very rare, accounting for only 2% to 4% of all primary bone neoplasms and 1% to 7% of all primary spinal tumors.1 Surgical resection, when possible, has the best long-term prognosis for most sacral tumors.2 Nonetheless, the surgical treatment of tumors in this area is challenging because of the complex regional anatomy and, often, the advanced stage of cancer at the time of diagnosis. Surgeons must not only be cognizant of local anatomy from a neurologic, colorectal, urologic, and orthopaedic standpoint, but also sometimes face the difficult conflict between functional preservation of the individual and cure of the disease process. The operating strategy requires precise and rigorous preoperative planning to locate the exact levels of tissue involvement; to make an accurate assessment of the bone, muscle, nerve, and joint structures that will require resection; and to plan pelvic reconstruction.2 This chapter focuses only on regional challenges to sacral tumors, as the anatomy and surgical approaches to the sacrum are covered more extensively elsewhere in this textbook.

Clinical Presentation

Sacral neoplasms usually grow insidiously. As a result, patients typically present with long-standing (several months to years) nonspecific symptoms, such as low-back, buttock, sacrococcygeal, or referred leg pain.1,3,4 Conventional radiographs are not sensitive, and routine lumbar myelography, CT, and MRI studies often fail to visualize the sacrum below the S2 segment. Unfortunately, many patients are misdiagnosed with lumbar disc disease for which they undergo subsequent management.

Although aggressive tumors can present earlier, the mean time to diagnosis from onset of symptoms has been reported to be 2 years.5 As a result of this common delay in making the appropriate diagnosis, sacral tumors may grow to advanced stages, with large dimensions and involvement of proximal organs and sacral nerves. According to Payer, an expansive space-occupying lesion of the sacrum usually leads to a specific pattern of clinical signs and symptoms throughout its natural history, depending on the anatomic location of the lesion within the sacrum, its extension, and whether there is compression or invasion of neighboring structures.6 Some sacral tumors have characteristic syndromes of pain due to their anatomic location and pattern of growth (chordomas, for example, may produce continuous rectal pain). 710

The first sign of disease may be a painless, visible sacral mass, although some patients may present with neurologic symptoms, with or without pain.11 The most common initial manifestation is local pain from mass effect.6 With subsequent tumor growth and impingement on and/or infiltration of local nerve roots, patients develop radicular pain, radiating into the buttocks, posterior thigh or leg, external genitalia, and perineum.5,12 Sacral tumor pain predominates at night and can be exacerbated by Valsalva maneuvers.5,13 Specific involvement of lumbosacral nerve roots will lead to characteristic neurologic deficits defined by the nerve or nerves involved.

Several non-neurologic clinical manifestations also can arise from sacral tumors as a result of invasion of neighboring structures. Ventral extension of a large sacral mass can present with constipation from rectal compression, as well as impede bladder emptying and uterine function.3,1417 Lateral extension across the sacroiliac and pelvic joints can result in local joint pain that is exacerbated by weight bearing and ambulation.13,18 Constitutional symptoms such as weight loss, blood abnormalities, or weakness typically are more characteristic of metastatic lesions than of primary sacral tumors.11

By the time a sacral lesion is diagnosed, many patients may have already been mistakenly treated for lumbar spondylotic problems. Presenting factors in sacral tumors, however, may be differentiated by their insidious onset, unilaterality, and progression to involve bowel and bladder continence and/or sexual function.6,19 A small sacral mass may even be palpable on digital rectal examination during the very early stages.11

Management Consideration: Biopsy

The combination of anatomic localization and imaging characteristics, when taken in the context of a specific clinical setting, often shortens the list of possible pathologic diagnoses. Preoperative biopsy is critical to establishing a surgical plan and can be reserved for those patients in whom exact knowledge of the pathologic diagnosis would influence the decision to operate or would alter the scope of surgery. If a primary rectal malignancy with local involvement of the sacrum is suspected, endoscopy with biopsy of any suspicious endoluminal lesions is appropriate. In the case of masses extrinsic to the rectal mucosa, transrectal biopsy is discouraged, because this violation of previously uninvolved tissue planes could then commit the patient to an otherwise unneeded bowel resection.

Although open biopsies and transrectal biopsies were common in the past, almost all biopsies are now performed using image guidance. The trajectory of the biopsy should be considered to allow for its easy inclusion within the boundaries of any subsequent surgical resection. Biopsy has particular relevance in hematopoietic malignancies that may be best treated with irradiation and combination chemotherapy. Lesions that are metastatic to the sacrum from remote sites are considered for operation only under special circumstances. Because this rarely occurs outside the context of a known primary tumor with widely disseminated disease, this is an uncommon indication for biopsy. In patients who are deemed unsuitable for a major operative procedure because of comorbid medical conditions, a biopsy is warranted to establish a diagnosis and direct the most appropriate therapeutic alternatives.

Most primary malignancies of the sacrum are locally aggressive tumors, metastasizing only late in the course of disease or not at all. Nonetheless, chest radiography and CT of the chest and abdomen, as well as a bone scan, are probably prudent, because evidence of remote disease may alter the decision for surgery and the method of treatment. Cancers of the rectum and pelvic organs with sacral involvement must be thoroughly staged before any consideration is given to surgery.

Tumor Classification

When considering surgical objectives in dealing with tumors of the sacrum, one must appraise the anatomic extent of the lesion and its biologic behavior. The anatomic considerations will direct the surgeon to the lesion, whereas the biologic considerations will dictate the scope of the surgery. One important variable to consider is whether the tumor is contained within its anatomic borders or has a fundamentally infiltrative or invasive nature. Approximately one half of sacral tumors are benign, encapsulated tumors and can be dealt with by lesional resection. Low-grade malignancies with infiltrative borders require more aggressive approaches with en bloc resection and a wide local excision with a circumferential margin of uninvolved tissue to effect cure. Certain higher-grade or disseminated malignancies are best treated not with surgical resection, but with radiation therapy or chemotherapy.

Sacral tumors can be classified according to four broad categories: congenital, metastatic, primary osseous, and primary neurogenic.7 Specific tumor management considerations are described in the following sections.

Congenital Lesions

Congenital lesions include dermoid cysts, anterior and intrasacral meningoceles, perineural (Tarlov) cysts, teratomas, hamartomas, and chordomas. Chordoma is the most common primary neoplasm of the sacrum.15,18,2024 These tumors typically are slow-growing, locally invasive tumors that arise from remnants of the notochord. Approximately 50% of chordomas are located in the sacrum. They can reach a large size before any symptoms manifest. These tumors typically are avascular, with a large soft tissue component centered on the midline, and expand into the presacral space. Patients at diagnosis typically are 40 to 70 years of age. They may suffer from local pain, which can be sharp or dull, usually is continuous, and often is located in the rectum, or they may present with sacral radicular pain or leg weakness and/or bladder and bowel dysfunction.3,6,17,25 Although infiltration of the gluteal muscles has been observed, the tumor does not typically involve the rectum ventrally through the presacral fascia.14,15,17 The duration of disease-free survival depends on the degree of resection; therefore, resection should extend at least one sacral segment beyond any obvious tumor involvement.3,14,26,27 Subtotal resection or curettage is done only when palliative treatment alone has been chosen because residual tumor is certain to progress.28 Chemotherapy has not demonstrated convincing efficacy, and radiation is reserved for unresectable residual or recurrent disease because it has been shown to delay time to tumor progression.29

Metastatic Tumors

Metastatic tumors are the most common malignant neoplasm in the sacrum.19 These tumors most often arise by hematogenous dissemination from solid organs such as the breast, lung, prostate, kidney, gastrointestinal tract, and thyroid.30 Hematogenous malignant tumors, such as multiple myeloma, also can metastasize to the sacrum or may occur as primary lesions, as is the case with lymphoma.19,31,32 Multiple myeloma and primary lymphoma are the second and third most common primary malignant neoplasms of the sacrum, respectively.33 Pelvic organ tumors, such as adenocarcinoma of the rectum, can even infiltrate the sacrum directly.11 Because of their rapid progression and locally invasive nature, metastatic tumors often are diagnosed earlier than primary sacral lesions.31 Unfortunately, sacral involvement typically signals advanced metastatic disease: once sacral metastases are detected, 61% of cases will have distant organ involvement, and 43% of cases may have involvement of other vertebrae.4,19

Consequently, treatment often is limited to palliative radiation and/or chemotherapy. Palliative surgical intervention sometimes is indicated for decompression of neural or pelvic structures in the absence of active systemic disease. Sacrectomy may be indicated with an extended abdominoperineal resection or pelvic exenteration for locally invasive pelvic tumors in carefully selected patients.7,19

Primary Osseous Tumors

Primary osseous tumors, although histologically and biologically diverse, account for less than 10% of all primary bone tumors.7

Low-grade tumors, which include osteoid osteoma, osteoblastoma, osteochondroma, and aneurysmal bone cyst (ABC), often are incidental findings and can present in a variety of ways. Osteoblastoma is distinguished by a lesional diameter greater than 2 cm and can present with a poorly localized, dull ache.34 Osteoid osteomas, on the other hand, produce localizing pain that is classically worse at night and is relieved by aspirin.2 Osteochondromas are slow-growing, cartilage-forming lesions that favor the dorsal elements, especially the facet joints. ABCs are composed of dilated vascular channels arising within an expanded marrow cavity. They preferentially arise in the dorsal elements but may involve the entire the sacrum. ABCs typically are discovered in individuals younger than 20 years of age, and, while histologically benign, are capable of significant sacral destruction and neurologic deficit.2,35 Most of these lesions follow an indolent course even without treatment and may even regress spontaneously. The preferred treatment is en bloc surgical resection, but curettage or subtotal resection may lead to a resolution of symptoms.

High-grade osseous tumors, which include chondrosarcoma, osteosarcoma, and Ewing sarcoma, often are very aggressive. Because these tumors respond poorly to chemotherapy and irradiation, they require a wide excision in the absence of systemic disease.3639 Osteosarcoma sometimes is the consequence of malignant transformation of a giant cell tumor or of Paget disease. Chondrosarcoma tends to be less aggressive. Ewing sarcoma is a small, round cell malignancy of childhood and adolescence that usually originates in bone but also may arise at extraskeletal sites. Ewing sarcoma and primitive neuroectodermal tumor are regarded as closely related members of the same family of tumors. Ewing sarcoma can occur as a primary sacral lesion but has one of the highest mortality rates of all bone tumors. Ewing sarcoma is regarded as a surgical condition only when encountered in the sacrum because of its propensity to metastasize early and because of its favorable response to both irradiation and chemotherapy.40

Giant cell tumors are the second most common primary tumor of the sacrum and usually peak in the third decade of life, with a predominance in women.18,23,24,4143 Although these tumors are histologically benign, they can degenerate into malignant sarcomatous tumors or even develop distant metastases.18,4144 Giant cell tumors typically are slow growing but can be locally invasive and attain a very large size by the time a diagnosis is made.38 Because these tumors can have a high rate of recurrence, the preferred treatment is total resection, which may include a total sacrectomy if the tumor crosses the midline, involves the upper sacral segments, or involves the sacroiliac joints.7,45 Good local control has been reported for curettage combined with bone cement and adjunctive cryosurgery.46,47 The role of radiotherapy remains unclear, because it has been implicated in the sarcomatous transformation.42

Primary Neurogenic Tumors

Primary neurogenic tumors of the sacrum, which are relatively rare, include schwannomas, neurofibromas, ganglioneuromas, and ependymomas. Only about 1% to 5% of spinal schwannomas arise at this level.48 Similar to neurogenic lesions elsewhere in the spine, they tend to originate in the spinal canal or in close relation to the nerve roots or their coverings. These tumors typically are slow growing, often are encapsulated, are intradural or extradural, and do not invade local tissue.7 The location and slow growth of these tumors allow them to expand and fill the sacral canal and grow out of the ventral or dorsal sacral foramina to variable degrees. These tumors often remain confined to the spinal canal and may be treated with lesional excision, similar to neurogenic tumors elsewhere in the spine. In cases where the tumor is of long standing, the sacrum can become excavated from the expansion and, although the tumor maintains its bony margin, there is a “pushing” rather than an infiltrative border. Giant sacral neurofibromas, schwannomas, and ependymomas occur with equal rarity. Dorsal approaches for a curative resection are possible for schwannomas and neurofibromas, but tumors with large presacral components may require an anterior transabdominal approach.38 Ependymomas can present both intradurally and extradurally in the sacroccygeal region and can be diagnosed in advanced stages with extensive bony destruction.7 Ependymomas require complete en bloc resection to prevent local recurrence or neuroaxis dissemination via the cerebrospinal fluid. Ganglioneuromas are rare, slow-growing tumors that can grow in the pelvis from sacral extensions of the sympathetic chain. The preferred treatment is complete resection with a combined ventral and dorsal approach.38

Surgical Approaches

The complex regional anatomy, biomechanical factors, and characteristics of sacral tumors make operations in this area particularly challenging. Surgery often is performed by a multidisciplinary team that includes spine, colorectal, vascular, and plastic surgeons. Once the decision to operate has been made, the approach is dictated by several factors: the patient’s preoperative status, tumor pathology, the amount of intrapelvic disease, the degree of sacral destruction (especially the sacral ala) and presence of sacroiliac joint involvement, and whether the surgical goal is palliation or cure. Patients must be carefully selected, because sacral resections can be highly morbid procedures with subsequent permanent motor or sensory deficits or loss of bowel, bladder, and/or sexual function.7,49 In cases of planned major sacral resections, it is advisable to obtain baseline urodynamic studies to assess preoperative voiding function.

Dorsal approaches to the sacrum are the simplest and include simple laminectomy, alone or combined with sacrococcygectomy. Sacral approaches can be performed with the patient in either the prone or lateral decubitus position. The advantages of the prone position are the ease of patient positioning, its familiarity and comfort for the operator, the facilitated use of the surgical microscope, and the opportunity for participation by the assistant surgeon. The major advantages of the lateral position are good abdominal relaxation and resultant lowering of pressure within the inferior vena cava and epidural veins, gravitational drainage of blood out of the wound, and the option it affords for synchronous ventral exposure of the sacrum via the transperitoneal or retroperitoneal route. For complex resections, the sacrum may be approached ventrally and dorsally.

Sacral Laminectomy

The principles of dorsal dissection and exposure are fundamentally similar to those employed during lumbar laminectomy. The proximity of the incision to the anal orifice and the increased potential for wound contamination warrant extra care in skin preparation and surgical draping. A midline incision usually is chosen. The sacrospinalis, multifidus, and gluteus maximus muscles are reflected laterally off the sacrum, and blood vessels often are found penetrating the dorsal sacral foramina. Sacrifice of the dorsal rami is unavoidable but does not lead to serious functional consequences. Because of the physiologic lordosis at the lumbosacral junction, the S1 and S2 laminae may be perceived as sloping upward with respect to the L5 lamina. The laminectomy usually is started at the L5-S1 hiatus, because the interlaminar space provides a convenient point of entry into the rostral sacral canal. More restricted openings directly into the midsacral and distal sacral canals over a well-localized and very limited lesion are possible. The small advantage gained in preserving the integrity of the dorsal ligamentous attachments at L5-S1 usually is counteracted by the restricted exposure and the lost opportunity to orient to the thecal sac and exiting nerve roots. Because the ventral sacrum is fused, sacral laminectomy is not significantly destabilizing, as long as the sacroiliac joints remain intact. The lower sacral nerve roots and the filum terminale exit from the termination of the dural sac at the S2 level. The only other normal constituents of the sacral canal are the epidural vessels and fat.

Sacral laminectomy is an appropriate approach to pathologic conditions originating within and largely confined to the sacral canal because of the ease with which the neural elements and their coverings are exposed. Sacral laminectomy is less well suited as a definitive exposure in lesions that originate outside the sacral canal or that have developed significant extension into the pelvis via the neural foramina or through sacral replacement, or for those tumors requiring an en bloc resection.

Treatment of neurogenic tumors and cysts is the foremost indication for the sacral approach. Lesions such as schwannomas, neurofibromas, and ependymomas may burrow into the ventral and lateral sacral elements, but this is not necessarily a limitation to the use of this exposure. Rarely is the destruction so extensive as to compromise sacroiliac joint stability. The great majority of these tumors are benign and are cured by intralesional/marginal resection of the tumor and its capsule. With a dorsal approach, even large tumors can be extricated successfully from the recesses of the sacrum. Intimate involvement with functional sacral roots is the most common impediment to total surgical extirpation of such tumors. Any dural defects should be closed in a watertight fashion, using a patch graft as necessary. If a wound drain is required, low-pressure suction bulb systems are most appropriate to minimize the risk of creating a cerebrospinal fluid fistula.