Introduction
Tumors of the sacrum and retrorectal space are rare. Two reviews of patients at the Cleveland Clinic found 50 patients between 1928 and 1985 ( Table 26-1 ) and 87 patients between 1981 and 2011, in line with other studies indicating that in major referral centers, 1.4 to 6.3 patients will be diagnosed with these tumors per year. The annual incidence of congenital retrorectal tumors is estimated to be from 0.0025% to 0.013%.
| Type of tumor | No. |
|---|---|
| Chordoma | 17 |
| Germ cell tumors | |
| Squamous cell carcinoma developing in a teratoma (teratoma with malignant transformation) | 1 |
| Endodermal sinus tumor (yolk sac tumor) | 2 |
| Mature teratoma | 13 |
| Tailgut cyst | 6 |
| Duplication cyst | 1 |
| Fibrosarcoma | 1 |
| Giant cell tumor of the sacrum | 3 |
| Aneurysmal bone cyst of the sacrum | 1 |
| Ewing sarcoma | 1 |
| Hemangiopericytoma | 1 |
| Neurogenic tumors | |
| Myxopapillary ependymoma | 1 |
| Lipomeningocele | 2 |
| TOTAL | 50 |
Anatomy of the Retrorectal Space
The retrorectal (presacral) space is a potential space that becomes apparent only when a mass expands into it. Anatomic descriptions of the area are inconsistent because of controversy over the nomenclature of the endopelvic fascia, and in particular, the definition of Waldeyer fascia. The most generally accepted definition describes the retrorectal space as bounded anteriorly by the mesorectal fascia and mesorectum, posteriorly by the presacral fascia over the sacrum and coccyx, superiorly by the peritoneal reflection, and inferiorly by the fusion of the rectal visceral fascia and the parietal presacral fascia over the levator ani and coccygeal muscles. Laterally, it is bounded by the iliac vessels and the ureters ( Fig. 26-1 ). It is divided into superior and inferior sections by the rectosacral fascia, which passes from S2, S3, or S4 to the rectum, inserting approximately 3 to 5 cm above the anorectal junction where it joins the mesorectal visceral fascia. The space normally contains loose connective tissue, the middle sacral artery, the iliolumbar vessels, the superior and middle hemorrhoidal vessels, lymphatics, and branches of the sympathetic and parasympathetic nervous systems. Some authors consider only the compartment superior to the rectosacral fascia to be the retrorectal space and label the inferior compartment the supralevator space.
The embryologic hindgut and the neuroectoderm fuse in the retrorectal space. As a result, many different kinds of tumors can be found there arising from ectodermal, endodermal, neural crest, or totipotential cells in the retrorectal space itself or from adjacent notochordal remnants, as well as cartilaginous and bony structures.
Classification Systems
Several classification systems for masses in the retrorectal space have been proposed. One of the most common, used by Uhlig and Johnson, divides these masses into five categories: (1) congenital, (2) inflammatory, (3) neurogenic, (4) osseous, and (5) miscellaneous. These categories were subdivided into benign and malignant by Dozois et al. Lev-Chelouche et al used four categories: (1) benign congenital, (2) malignant congenital, (3) benign acquired, and (4) malignant acquired. We adapted this classification, as shown in Box 26-1 . Finally, as an aid to operative planning, Papallardo et al. suggested a classification of tumors based on imaging findings according to the site of origin: (1) the presacral space, (2) the sacrum or spinal cord and growing anteriorly, and (3) the rectum and growing posteriorly. The most common lesions are described in the following sections.
Congenital/Developmental
Benign
Developmental cysts, teratoma
Duplication cysts
Anterior meningocele
Adrenal rest tumor
Malignant
Chordoma
Teratocarcinoma
Acquired Metaplastic
Neurogenic
Benign
Neurofibroma
Schwannoma
Ganglioneuroma
Malignant
Neuroblastoma
Ganglioneuroblastoma
Ependymoma
Neurosarcomas
Malignant schwannoma
Osseous
Benign
Giant cell tumor
Osteoblastoma
Aneurysmal bone cyst
Malignant
Osteogenic sarcoma
Ewing sarcoma
Myeloma
Chondrosarcoma
Other Metaplastic
Benign
Lipoma
Hemangioma
Fibroma
Leiomyoma
Endothelioma
Desmoid
Malignant
Liposarcoma
Hemangiopericytoma
Fibrosarcoma
Leiomyosarcoma
Metastatic carcinoma
Undetermined Malignant Potential
Gastrointestinal stromal tumor
Miscellaneous
Hematoma
Abscess
Congenital/Developmental Lesions
Developmental lesions may arise from embryonic mishaps involving primitive gut or neural structures.
Germ Cell Tumors
Germ cell tumors in the retroperitoneum and retrorectal space may be pure or mixed. The pure tumors include teratomas (mature or immature; Fig. 26-2 ), yolk sac tumors (endodermal sinus tumors), embryonal carcinomas, germinomas (histologically identical to seminomas), and choriocarcinomas. Only teratomas and yolk sac tumors are commonly seen in the sacrococcygeal region. All teratomas are composed of a mixture of tissue components derived from one or more of the three embryonic germ layers (ectoderm, mesoderm, and endoderm) and contain tissue foreign to the anatomic site of origin. Mature and immature teratomas are considered benign but may undergo malignant transformation of a somatic tissue—for example, squamous cell carcinoma originating in squamous epithelium or rhabdomyosarcoma developing in mesenchymal tissue. The terms “mature” and “immature” reflect histologic differentiation of teratomas.
Sacrococcygeal teratoma (SCT) is the most common presacral tumor of the newborn, with an incidence of 1 in 23,000 to 1 in 40,000 live births. The differential diagnosis of SCT includes lumbosacral myelomeningocele, neuroblastoma, glioma, hemangioma, neurofibroma, chordoma, leiomyoma, lipoma, and melanoma. Although it is possible that these tumors may arise from germ cells or may represent a form of fetus in fetu , the generally accepted theory is that they arise from totipotent somatic cells in the primitive knot (Hensen’s node) or caudal cell mass. The American Academy of Pediatrics Surgical Section classified these tumors according their location as follows:
Type I: Predominantly external (sacrococcygeal) with only a minimal presacral component
Type II: Presenting externally but with significant intrapelvic extension
Type III: Apparent externally but predominantly pelvic and extending into the abdomen
Type IV: Presacral with no external presentation; because there are no external signs of a mass in type IV, early diagnosis may be difficult and malignant transformation is common
Teratomas are more frequent in females than in males (5:1), and anomalies of the sacrum, urinary tract, or anorectum may accompany these lesions. An autosomal-dominant condition known as the Currarino triad, now known to be associated with an MNX1 gene mutation, was described in 1981 and consists of (1) a presacral mass that may be a teratoma, meningocele, neurenteric cyst, or a combined lesion, (2) an anterior sacral defect, and (3) an anorectal malformation. The usual clinical prenatal presentation of SCT is a uterine size greater than gestational dates. Ultrasound reveals a solid or mixed solid and cystic lesion with increased vascular flow and polyhydramnios. Placentomegaly and high output cardiac failure as a result of tumor-associated arteriovenous fistulae also may be observed. Fetal magnetic resonance imaging (MRI) provides important anatomic detail. The mortality rate for SCT diagnosed in the newborn is 5% or less, but it approaches 50% when diagnosed in the fetus as a result of complications such as tumor rupture, hemorrhage, cardiac failure, and premature labor. Thus diagnosis of a fetal tumor should prompt referral to a specialty center, where early delivery or fetal surgery may be considered. The outcomes of open fetal procedures have only been studied retrospectively. Results of alcohol and radiofrequency ablative procedures and open interventions for hydrops have generally been poor, but cyst decompression to assist with delivery has been helpful.
Neonatal SCTs are usually resected along with the coccyx, and the rectum is carefully preserved. Type I and II lesions can usually be resected after delivery with the infant in the prone position. The coccyx is removed and buttock contouring reconstruction is performed. Larger tumors may require a combined abdominal and posterior approach or vascular control of the median sacral artery, which can be achieved laparoscopically before posterior resection. Urologic comorbidities are frequent (64%) in infants with SCT, and a plan for urologic surveillance is important. Although SCTs are generally benign, local recurrence after resection is common. Surveillance with digital rectal examination and ultrasound, measurement of alpha fetoprotein levels every 3 months, and pelvic MRI yearly is recommended for at least 3 years.
In the past, malignant germ cell tumors had a dismal prognosis, but current chemotherapy regimens have markedly improved survival, although neuropathic bladder or bowel abnormalities have been seen in 11% to 41% of survivors. Other long-term complications can include chronic lung disease, developmental delay, chronic bowel dysfunction, and the need for scar revision.
Tailgut Cysts
Tailgut cysts, also called retrorectal cystic hamartomas, are multilocular cysts whose histologic features are similar to and consistent with derivation from aberrant remnants of the postanal gut (incomplete involution of the embryonic tailgut). Early in fetal development, the primitive gut extends caudal to the point where the anus develops and then subsequently regresses. Remnants of this primitive structure may then give rise to congenital cysts. The neurenteric canal, which connects the amnion to the yolk sac around the sixteenth day of development, may also be a source of some lesions. Tailgut cysts may be lined by squamous, transitional, or columnar epithelium. The columnar epithelium may be ciliated or may contain mucin. Often there is an abrupt change from one type of epithelium to another. Muscle bundles in the cyst wall are disorganized. Tailgut cysts lack dermal appendages and mesenchymal derivatives other than smooth muscle, fibrous tissue, and blood vessels, and they do not contain immature elements. These lesions may become quite large and occasionally develop into adenocarcinomas or carcinoid tumors ( Fig. 26-3 ). There is a strong female predominance (3:1), and the average age at presentation is 36 years. These benign lesions are frequently misdiagnosed. Patients are often thought to have a perirectal abscess, leading to misguided attempts at incision and drainage before definitive resection is performed. A history of recurrent abscesses or perianal fistulas without an internal opening should alert the surgeon to the possibility of a retrorectal cystic lesion. Recurrence is frequent and is a result of incomplete excision.
Duplication Cysts
The hindgut is the least frequent site for duplication anomalies. Presenting symptoms and signs include abdominal distention, vomiting, failure to thrive, constipation, diarrhea, and hematochezia. Two forms of duplication cysts are recognized: (1) a limited tubular form of duplication on the mesenteric aspect of the gastrointestinal tract in which the epithelium may be squamous, columnar, or mixed, and (2) a kind of abortive caudal twinning with duplication of the rectum, anus, genitalia. Complete duplication of the colon, rectum, urinary tract, and external genitalia is extremely rare. Associated cleft vertebrae, mediastinal or intraspinal cysts, or a dorsal sinus tract may be present. Unlike retrorectal cystic hamartomas, duplication cysts are generally surrounded by a well-formed smooth muscle coat.
Occasionally, the tubular duplication may communicate at some point with the intestine, leading to stagnation of intestinal contents within the blind pouch. Gastric mucosa with fistula formation and malignant tumors have been reported in duplication cysts of the rectum. Therefore, it is suggested that the mucosa be peeled out if the cyst cannot be removed. Some authors have reported successful removal of duplication cysts via transanal endoscopic microsurgery.
Management of the caudal twinning anomaly is exceedingly complex. Smith classified these lesions as follows: Type 1 duplications with two separate perineal ani, type 2 duplications with one or both rectums terminating in a fistula to the urogenital tract, and type 3 duplications with one external anus and one anal atresia in the pelvis. Type 1 lesions may not require any treatment if the patient is asymptomatic. Patients with type 2 lesions usually present with intestinal obstruction early in life. Duplication of the external genitalia is frequent. If one normal anus is present, the fistula can be closed and the duplication can be anastomosed to the other colon. If both colons end in a fistula, a diverting colostomy should be performed, and the anatomy should be ascertained by radiologic studies. In some cases, external urinary diversion also may be required to treat incontinence. If a functional puborectalis sling exists, the rectum may be brought down to the perineum at a later date. Type 3 anomalies are usually difficult to diagnose, and for that reason, patients with these anomalies often do poorly. Treatment consists of dividing the common septum between the two lumens or excising the blind colon.
Anterior Sacral Meningocele
Anterior sacral meningocele (ASM) is a rare form of spinal dysraphism characterized by an anterior hernia of the meningocele sac through a sacral defect or neural foramen. The meningocele sac is located in the presacral space and contains cerebrospinal fluid and sometimes neural elements. It may be associated with Currarino syndrome, spina bifida, a tethered spinal cord, uterine and vaginal duplication, kidney or bladder malformation, perianal fistula, imperforate anus, anal atresia, or anal stenosis. Germ cell tumors and presacral lipomas have also been associated with meningoceles. Pressure from the ASM on the sacral nerve roots, rectum, bladder, and genitalia can cause complaints of headache associated with bowel movements or other straining, lower back and pelvic pain, constipation, difficulties in defecation, dysmenorrhea, dyspareunia, and urinary incontinence, retention, or urgency. These lesions can be mistaken for ovarian cysts. The finding of a “scimitar” sacrum, characterized by a rounded, concave border with no bone destruction in the remaining sacrum, is pathognomonic. ASM also can be seen in patients with Marfan syndrome or neurofibromatosis, in which case the sacral foramen may simply be widened, with the scimitar sign absent. MRI and computed tomography (CT) scans are usually diagnostic, but if communication with the dural sac is in doubt, myelography with metrizamide is recommended. Aspiration should be avoided because of the risk of meningitis. Treatment consists of opening the dura mater and obliterating the neck of meningocele. This procedure usually does not require the participation of an abdominal surgeon unless the sac is too large to be closed securely from the posterior approach or unless a tumor is associated with the meningocele, but the anterior approach can be helpful. Laparoscopic approaches have also been described.
Chordoma
Chordomas are malignant tumors thought to derive from remnants of the fetal notochord. Normally, the notochord is manifest in the adult as the nucleus pulposus of the intervertebral disks, but rests of notochordal tissue may remain in ectopic positions. Approximately 300 cases per year are diagnosed in the United States. Chordomas represent approximately 1% to 5% of primary bone tumors and less than 1% of all central nervous system tumors. Fifty percent to 60% occur within the sacrococcygeal area, and they constitute more than 50% of primary tumors of the sacrum. Other common sites include the base of the skull and the vertebrae. Most series have noted a male predominance for the sacrococcygeal lesions, with a ratio of approximately 2:1. Although they may occur at any age, the greatest incidence is between the ages of 40 to 70 years.
Chordomas are slow growing, locally aggressive, and resistant to radiotherapy. They may be gelatinous or firm, depending on the amount of mucinous material present. Hemorrhage and necrosis may lead to cyst formation or secondary calcification. A pseudocapsule is often present, and invasion of bone frequently occurs. Microscopically, one sees a lobular framework with fibrous septa containing variable amounts of vacuolated physaliferous cells and extracellular mucin.
Common presenting complaints include buttock or back pain, numbness in the perianal region, buttock, or leg, difficulty voiding, and constipation. Muscle weakness is also frequent. Rectal masses are usually palpable, but it is difficult to assess the size of the tumor upon digital examination. Radiographs of the pelvis will show abnormalities such as sacral bone erosion or calcification in approximately 50% of patients. CT scanning and MRI give an accurate assessment of the size of the mass and bone invasion ( Fig. 26-4 ).
