Retrorectal Tumors

Julio Garcia-Aguilar, MD, PhD
Clinical Associate Professor
University of Minnesota
Minneapolis, MN

The retrorectal space is the loose areolar plane located between the fascia propria of the rectum and the presacral space. The pelvic continuation of the retroperitoneal space, it is limited inferiorly by the rectosacral fascia, which separates the retrorectal space from the supralevator space. The lateral limits of the retrorectal space are less well defined; they include the hypogastric vessels, the ureters and the lateral stalks of the rectum.

The retrorectal space is an area where the neuroectoderm, the notochord, the hindgut and the proctodeum undergo remodeling and regression in embryological life. It can thus be the site of a heterogeneous group of benign and malignant tumors originating from vestigial tissue derived from the three germinal layers. Some tumors that are considered retrorectal , such as chordomas, originate in the sacrum; accordingly some sacral tumors are also considered retrorectal tumors.

Retrorectal tumors are rare. Most publications describe only individual cases. Few series from large institutions include enough cases to estimate the overall incidence or relative frequency of these tumors. Uhlig and Johnson noted 63 patients with retrorectal tumors treated over a 30-year period in a major metropolitan area. Jao et al. reported on 120 patients with retrorectal tumors treated at the Mayo Clinic over a 20-year period. They represented 1 in every 40,000 general hospital admissions. The Cleveland Clinic reported 24 cases of sacral and retrorectal tumors between 1980 and 1992.

Retrorectal tumors are usually classified as congenital, inflammatory, neurogenic, osseous, or miscellaneous. According to the combined experience of seven different published series, congenital lesions comprised 63% of retrorectal tumors, inflammatory, 8%; neurogenic, 10%; osseous, 7%; and miscellaneous 12%. In all, 30% to 45% are malignant. The risk of malignancy is higher for solid tumors (60%) than for cystic lesions (10%). The relative frequency of retrorectal tumors is different in children, in whom teratomas and myelomeningocele are most common.

Some patients are asymptomatic, and their retrorectal tumor is discovered incidentally. But most patients with complain of nonspecific symptoms for a period of time before the diagnosis is made. The most common symptoms are sacral or lumbar pain, urinary or bowel dysfunction, recurrent drainage, and neurologic deficit. Benign and malignant tumors have similar symptoms, which depend more on the size of the tumor than on its histologic nature. Nearly all retrorectal tumors are palpable by digital exam. Computed tomography (CT) and magnetic resonance imaging (MRI) are the most accurate diagnostic tools. They yield valuable information on sacral involvement, soft tissue invasion, extension, and relationship with adjacent structures. Endorectal ultrasound (ERUS) provides useful information on cystic lesions. Other diagnostic tests (e.g., sigmoidoscopy, intravenous pyelogram, myelography) may be used selectively.

Presacral lesions can only be precisely diagnosed by histologic characteristics. However, the role of preoperative biopsy is controversial. Biopsies have been associated with abscess formation, fecal fistula, meningitis, and tumor seeding in the biopsy tract. Most authors consider operative excision or frozen biopsy during surgery the best biopsy method. They claim that these tumors should be removed because they can be malignant, because teratomas may undergo malignant degeneration, and because cystic lesions may become infected. Biopsy may be indicated if resection is unlikely or risky and the if suspected lesion can be treated without surgery.

Congenital lesions are the most common retrorectal tumors; two thirds of them are cystic, one third solid. Most cystic lesions of the retrorectal space probably develop from embryonic remnants, but the classification and terminology are rather confusing. From the practical perspective, presacral cysts that contain histologic elements from a single germ-cell layer are classified as developmental cysts. Cystic tumors that contain elements from more than one germ-cell layer are classified as teratomas. Duplication cysts have a well-defined muscular wall with myenteric plexus. Chordomas are the most common solid tumor, but other solid tumors, such as adrenal rests, are rare.

Developmental Cysts
Developmental cysts often contain columnar or transitional epithelium (tailgut cysts or mucus-secreting cysts) or squamous epithelium with (dermoid cysts) or without (epidermoid cysts) skin appendages. A single layer of epithelium lines most cysts; in most cases, more than one type of epithelium can be identified. Disorganized bundles of smooth muscle fibers are often found in the vicinity of the cysts, most of which are multilocular. The average diameter is close to 4 cm. The fluid that fills these cysts varies from thin, clear and colorless to opaque and pasty. These cysts usually do not communicate with the rectum. Associated sacrococcygeal abnormalities have been described, but are rare. Malignant transformation is also rare.

More common in females, developmental cysts are often diagnosed in the fourth and fifth decade of life. They are often asymptomatic and are discovered incidentally during anal digital exam as a soft, compressible, ill-defined mass behind the rectum. Some patients complain of pain, particularly when sitting, and some relate the development of symptoms to a fall on their buttocks. Developmental cysts can become infected and be confused with a supralevator abscess or a fistula-in-ano. Some patients undergo several operations times before a definitive diagnosis is made. Symptoms tend to be a function of the cyst's size and location and of the presence of infection. A funnel- shaped dimple in the postanal area or in the posterior aspect of the anal canal, below the dentate line, can be confused with a fistulous opening. This dimple, which has been reported in 30% to 100% of patients with developmental cysts, may or may not communicate with the cyst.

Differentiating between an infected retrorectal cyst and a fistula-in-ano with a supralevator extension may be difficult. The diagnosis of a retrorectal cyst is suggested by the lack of a primary opening at the level of the dentate line, by the presence of a postanal dimple, and by the sensation of fixation and fullness in the retrorectal space suggest.

The radiographic aspect of the sacrum is usually normal. Barium enema and colonoscopy confirm the presence of an extrinsic retrorectal mass in half of these patients. The diagnosis is often confirmed by CT, MRI or ERUS. ERUS is particularly useful in delineating the relationship of cysts with the rectal wall and in assessing multilocular cysts. MRI is best at delineating the relationship of cysts with the levator muscles.

Most authors recommend removing all retrorectal cysts, even when asymptomatic. Removing them will help confirm the diagnosis, exclude malignancy, and to prevent infection. Most developmental cysts are low and can be easily removed by a posterior parasacrococcygeal approach. Infected cysts should be drained through the rectum. Once the infection is controlled, the cyst can be safely removed by a posterior approach. The opening in the rectal wall is then closed with interrupted reabsorbable sutures.

Anterior Sacral Meningocele
Anterior sacral meningocele (ASM) is a rare retrorectal tumor that affects predominantly females. It is a congenital herniation of the dural sac through a defect in the anterior wall of the sacrum. The sac, composed of an outer dural membrane and an inner arachnoid membrane, contains cerebrospinal fluid. When the sac contains neural elements it is called a myelomeningocele. Most clinical manifestations (e.g., constipation, urinary difficulties, low back pain) are caused by pressure of the ASM on adjacent structures. Pressure on the meningocele (e.g., straining during defecation, squatting, intercourse) displaces the cerebrospinal fluid through the stalk and causes a sudden increase in the intracranial pressure, resulting in a headache.

An ASM is usually felt as a soft, cystic mass adherent to the sacrum. A pelvic X- ray demonstrating a concave defect in one side of the sacrum - a scimitar sacrum - is diagnostic. Myelography, CT and MRI are useful in delineating the anatomy of the stalk and in planning the operation. Aspiration should be avoided because of the risk of meningitis.

Asymptomatic meningoceles should be operated on if they increase in size and if there is a chance of pregnancy. For symptomatic patients, surgery is the treatment of choice. The goal of surgery is a watertight obliteration of the dura at the sacral side. The neck can be approached by posterior transacral laminectomy or through the abdomen. The posterior approach is safe and allows identification of the nerve roots, but wide stalks may not be closed this way. The anterior approach provides better exposure of the stalk and allows better dissection of the cyst, but carries a higher risk of complications. The closure of the stalk can be tested by increasing the cerebrospinal fluid pressure (which can be done by compressing the jugular veins).

Teratomas
Teratomas are true neoplasms that originate in totipotential cells abnormally present in sequestered midline embryonic rests. Teratomas contain recognizable mature or immature elements representative of more than one germ layer. The sacrococcygeal area is the most frequent site of teratomas in infancy, occurring in 1 of 35,000 to 40,000 births. In adults, sacrococcygeal teratomas are rare, and are likely to be congenital. Teratomas in infancy are externally visible in most patients, but sacrococcygeal teratomas in adults are mostly confined to the retrorectal space. They are often cystic, although they may be also solid. Microscopically, teratomas contain a variety of tissues from more than one germ layer. Depending on the degree of differentiation of their components, teratomas are classified as mature, immature, or malignant. Mature teratomas contain mature epithelial and mesenchymal tissues. Immature teratomas have areas of primitive endoderm, mesoderm and ectoderm mixed with more mature elements. Malignant teratomas contain malignant tissue of germ cell origin such as embryonal tissue, germinoma, and choriocarcinoma. Teratomas that contain malignant non-germ cell elements, presumably derived from somatic tissue within the teratoma, are called teratomas with malignant transformation. Most teratomas in infancy and childhood are benign. In the pediatric population, there is a tendency toward development of malignant teratomas with increasing age. However, most teratomas in adults are benign.

Sacrococcygeal pain and perianal drainage are common symptoms. But some tumors are incidentally discovered during physical exam. Radiographic evidence of bone destruction is uncommon. Calcification inside the tumor is present in one fourth of the tumors. A pelvic CT or MRI helps confirm the diagnosis and extension inside the pelvis.

The primary treatment of all primary sacrococcygeal teratomas is surgical excision. Most teratomas in adults can be excised by a posterior parasacrococcygeal approach. However, teratomas that extend proximally in the pelvis have to be removed by a combined abdominal and posterior approach. In patients with teratomas, the coccyx often contain nests of totipotential cells and therefore it should be removed en block with the tumor. Failure to remove the coccyx has been associated with a high risk of recurrence. For mature and immature teratomas, the prognosis is good after surgical excision alone, but malignant teratomas have a tendency to recur and metastasize. Therefore, patients with malignant teratomas should receive adjuvant therapy, but because such tumors are so infrequent, no standard recommendations exist for either chemotherapy or radiation therapy. Teratomas with malignant transformation are often resistant to chemotherapy.

Chordomas
Chordomas are rare neoplasms originating from notochordal remnants. They represent less than 3% of all primary bone tumors, but 50% are located in the retrorectal area. They affect individuals in the sixth and seven decade of life and are more common in males. They are slow-growing and locally invasive into the bone and surrounding soft tissue. They metastasize in 15% to 25% of patients.

A dull buttock or lumbar pain is usually the initial manifestation. Constipation, bladder dysfunction, and neurologic deficits in the lower extremities are late symptoms. Most chordomas are palpable by digital exam. Most patients have radiographic evidence of bone destruction, trabeculation, or calcification. CT and MRI give an accurate assessment of size and extension.

Chordomas are lobulated, gelatinous tumors with areas of hemorrhage, cystic changes, or calcification. Histologically, they contain cell aggregates separated by stromal tissue. In the center of the tumor, cords of cells with poorly defined boundaries seem to be floating in mucus. The physaliferous cells - which are large vacuolated cells - are pathognomonic.

Surgical treatment requires en block resection with tumor-free margins and no tumor entry. Distal tumors can be resected by a posterior approach, but tumors with pelvic or high sacral extension are best treated by a sequential abdominal and posterior approach. Local recurrence is high, even after a resection with negative margins. Localio recommends extending the resection one sacral segment above the tumor's radiological extension. For large tumors, complete resection is almost impossible, and yet partial excision is invariably followed by local recurrence. The use of adjuvant conventional radiation therapy, even at high doses, has been disappointing. High-linear energy transfer therapy has yielded promising results in patients with inoperable tumors or with macroscopic residual tumor. With a multimodal approach, a 5-year survival rate of 85% and a local control rate of 55% can be expected.

Most inflammatory lesions are related to perirectal absceses. The finding of a primary opening at the level of the dentate line suggests a criptoglandular infection. Of note, a chronic pelvic suppurative process secondary to diverticulitis or Crohn's disease can be confused with retrorectal tumors. Foreign body granulomas (secondary to oil-based injections used for hemorrhoid treatment or to rectal perforation during barium enemas) are exceedingly rare today.

The most common neurologic tumors are neurilemomas, neurofibromas, ependymomas, ganglioneuromas, and neurofibrosarcomas. Two thirds of them are benign. Tumors developing in the retrorectal space can reach a large size before they become symptomatic. Tumors arising inside the spinal canal can cause devastating neurologic deficits. Complete resection is often curative.

The variety and biological behavior of osseous tumors in the retrorectal space is similar to that of bone tumors elsewhere in the body. Osteomas, simple bone cysts, osteosarcomas, Ewing's sarcomas, and aneurismal bone cysts are the most frequent.

The list of miscellaneous lesions is very long, but the most common are metastatic carcinomas and soft tissue sarcomas.

Carcinod tumors of the retrorectal space are rare, but deserve special consideration. Most represent direct extension or metastatic spread from rectal carcinoids. More common in females, they are often associated with developmental cysts. Most of them adopt a trabecular architectural arrangement, which is the pattern typically associated with rectal carcinoids. The main histologic differential diagnosis is with paragangliomas and myxopapillary ependymomas. Retrorectal carcinoids are potentially malignant. Surgery is the treatment of choice. Because of their frequent association with developmental cysts and their trabecular pattern, they are assumed to arise from neuroendocrine cells located in presacral hindgut cells.

References

1. McCune W. Management of Sacrococcygeal Tumors. Annals of Surgery 1964;159,6:911-917.
2. Freier DT, Stanley JC, Thompson NW. Retrorectal tumors in adults. Surg Gynecol Obstet 1971; 132:681-6.
3. Uhlig BE, Johnson RL. Presacral tumors and cysts in adults. Dis Colon Rectum 1975; 18:581-9.
4. Jao SW, Beart RW, Jr., Spencer RJ, Reiman HM, Ilstrup DM. Retrorectal tumors. Mayo Clinic experience, 1960-1979. Dis Colon Rectum 1985; 28:644-52.
5. Stewart RJ, Humphreys WG, Parks TG. The presentation and management of presacral tumours. Br J Surg 1986; 73:153-5.
6. Bohm B, Milsom JW, Fazio VW, Lavery IC, Church JM, Oakley JR. Our approach to the management of congenital presacral tumors in adults. Int J Colorectal Dis 1993; 8:134-8.
7. Cody HS, 3rd, Marcove RC, Quan SH. Malignant retrorectal tumors: 28 years' experience at Memorial Sloan-Kettering Cancer Center. Dis Colon Rectum 1981; 24:501-6.
8. Verazin G, Rosen L, Khubchandani IT, Sheets JA, Stasik JJ, Riether R. Retrorectal tumor: is biopsy risky? South Med J 1986; 79:1437-9.
9. Hjermstad BM, Helwig EB. Tailgut cysts. Report of 53 cases. Am J Clin Pathol 1988; 89:139-47.
10. Oren M, Lorber B, Lee SH, Truex RC, Jr., Gennaro AR. Anterior sacral meningocele: report of five cases and review of the literature. Dis Colon Rectum 1977; 20:492-505.
11. Lee SC, Chun YS, Jung SE, Park KW, Kim WK. Currarino triad: anorectal malformation, sacral bony abnormality, and presacral mass--a review of 11 cases. J Pediatr Surg 1997; 32:58-61.
12. Ng EW, Porcu P, Loehrer PJ, Sr. Sacrococcygeal teratoma in adults: case reports and a review of the literature. Cancer 1999; 86:1198-202.
13. Miles RM, Stewart GS, Jr. Sacrococcygeal teratomas in adult. Ann Surg 1974; 179:676-83.
14. Abel ME, Nelson R, Prasad ML, Pearl RK, Orsay CP, Abcarian H. Parasacrococcygeal approach for the resection of retrorectal developmental cysts. Dis Colon Rectum 1985; 28:855-8.
15. Localio SA, Eng K, Ranson JH. Abdominosacral approach for retrorectal tumors. Ann Surg 1980; 191:555-60.
16. Yonemoto T, Tatezaki S, Takenouchi T, Ishii T, Satoh T, Moriya H. The surgical management of sacrococcygeal chordoma. Cancer 1999; 85:878-83.
17. Breteau N, Demasure M, Lescrainier J, Sabbattier R, Michenet P. Sacrococcygeal chordomas: potential role of high LET therapy. Recent Results Cancer Res 1998; 150:148-55.