16 Retrorectal Tumors
Abstract
This chapter will discuss the most common retrorectal tumors, including their etiology and incidence, but will focus on a practical clinical approach to these tumors based on the best available evidence.
16.1 Introduction
The presacral or retrorectal region is an area of embryologic fusion and remodeling, and thus it is a common site for embryologic remnants from which a heterogeneous group of neoplasms can develop. When compared to most other diseases that a colorectal surgeon will encounter, retrorectal tumors are rare and, as a result, poorly studied. Most publications detailing the diagnosis and treatment of these cysts and neoplasms are retrospective and small.
Additionally, there has been very little research in recent years on the subject, with many of the classical teachings stemming from studies that were published over 40 years ago. Within these older studies is a great deal of heterogeneity in available imaging and the extent of preoperative evaluation. The operative approach was also variable, with high rates of margin positivity. This problem likely led to higher rates of recurrence and lower rates of long-term survival.
Since then, there have been significant advances in imaging, record-keeping, and adjuvant therapy, so certain interventions that were previously felt to be contraindicated have re-emerged as viable treatment options. Perhaps the most controversial of these possibilities is the role for preoperative biopsy of solid tumors, which now has a very well-defined role for select tumors. Additionally, there is emerging evidence that observation of benign-appearing lesions may be safe.
This chapter will discuss the most common retrorectal tumors, including their etiology and incidence, but will focus on a practical clinical approach to these tumors based on the best available evidence.
16.2 Anatomy
The retrorectal space lies between the upper two-thirds of the rectum and the sacrum, above the rectosacral fascia. It is anteriorly limited by the fascia propria covering the rectum, posteriorly by the presacral fascia, and laterally by the lateral ligaments (stalks) of the rectum, the ureters, and the iliac vessels. Superiorly, it is bounded by the peritoneal reflection of the rectum and communicates with the retroperitoneal space. Inferiorly, it is limited by the rectosacral (Waldeyer’s) fascia, which passes forward from the S4 vertebra to the rectum 3 to 5 cm proximal to the anorectal junction.
Below the rectosacral fascia is the supralevator space, a horseshoe-shaped potential space anteriorly limited by the fascia propria of the rectum and inferiorly by the levator ani muscle (▶ Fig. 16.1). This more inferior area is often included along with the true retrorectal space when describing presacral tumors.
The retroperitoneal space contains loose connective tissue. The presacral fascia protects the presacral vessels that lie deep to it. These vessels are part of the extensive vertebral plexus and are responsible for the major bleeding problems encountered in this area during surgery.
16.3 Classification
Uhlig and Johnson, 1 aided by the composite classification of Freier et al, 2 have proposed the classification outlined in the accompanying ▶ Table 16.1. In general, these tumors are divided into (1) congenital, including developmental cysts, chordomas, and anterior sacral meningoceles, (2) inflammatory, including anal fistulas, (3) neurogenic, (4) osseous, and (5) “miscellaneous” including several sarcomatous lesions and metastatic tumors.
Congenital |
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Inflammatory |
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Neurogenic |
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Osseous |
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Miscellaneous |
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When making clinical decisions, a more practical way to classify these tumors is into the broad categories of solid and cystic. Another practical distinction is between tumors that arise during infancy and early childhood versus those that arise in adulthood, as these tumors often behave quite differently.
16.4 Incidence
The true incidence of retrorectal tumors is unknown. It may be underestimated as these tumors likely remain undetected in a large percentage of asymptomatic individuals, and even when discovered, they are often mistaken for other anorectal pathologies such as abscesses and fistulas.
Most case series are quite small, and come from specialty centers that may see a disproportionate number of cases compared to the surrounding population. However, the most quoted incidence is about 1 in 40,000 hospital admissions, 3 , 4 , 5 derived from a 1985 case series involving 120 patients treated at the Mayo Clinic. 6
The relative incidence of this heterogeneous group of tumors is difficult to estimate, as most case series would inherently suffer from sample bias. In general, congenital lesions account for slightly more than half of all presacral tumors, and two-thirds of these lesions are developmental cysts. Neurogenic neoplasms account for 5 to 15% of lesions as well. 3 , 5 Thankfully, most retrorectal neoplasms are benign, but the most common malignant neoplasms are sacrococcygeal chordomas, followed by sarcomas. 6 , 7
16.5 Pathology
An exhaustive review of the pathology of this area is not given in this chapter. Many of the tumors have common symptoms and present in a similar manner; the reader is referred to any standard pathology text. However, the pertinent pathologic features of the most common tumors will be briefly reviewed.
16.5.1 Developmental Cysts
Developmental cysts may arise from any of the germ layers (▶ Table 16.2). All congenital cysts occur with a female predominance, 6 with a female-to-male ratio of incidence of 5:1. The majority of cysts are asymptomatic and, because tension in the cyst is low, their presence may be easily missed on rectal examination. The average age at cyst appearance is in the fourth decade. The duration of symptoms, if they exist, is frequently measured in years. A postanal dimple is associated with some congenital cysts and may be a clue to the diagnosis. While the exact rate of malignancy is not known, up to 12% of cystic lesions can develop into a malignancy. 8 , 9
While reported rates of these cysts have been higher in females, they were often asymptomatic, and were found during the reproductive years, when pelvic examinations are most frequent. Thus, the female predominance may be artificial to some extent. This fact also may impact the calculations which will be discussed later that show that men tend to have more malignant lesions.
Epidermoid and Dermoid Cysts
Epidermoid and dermoid cysts result from closure defects of the ectodermal tube with heterotopic inclusions of skin, sometimes with accessory skin appendages. The epidermoid cyst is lined with stratified squamous epithelium with keratohyaline granules and intracellular bridges. In addition to the stratified squamous epithelium seen in epidermoid cysts, dermoid cysts have sweat glands, hair follicles, sebaceous glands, or all three. These appendages characterize dermoid cysts.
Both epidermoid and dermoid cysts tend to be rounded and circumscribed, have a thin connective tissue outer layer, and contain viscid green-yellow material. These cysts can communicate with the skin surface, where they appear as a postanal dimple. The cysts have a 30% rate of infection. 10 In the infected state, they may appear as a retrorectal abscess or perirectal suppuration. When the postanal dimple communicates with an infected cyst, a mistaken diagnosis of anal fistula is commonly made.
Enterogenous Cysts
Enterogenous cysts result from sequestration of the developing hindgut, and may include squamous or transitional epithelium within the lining of an otherwise mucus-secreting cyst. Generally, these are thin-walled cysts lined by columnar epithelium, and they tend to be multilocular, usually with one dominant cyst and a series of minor or “daughter” cysts. In the uninfected state, they are filled with a clear to green mucoid material. Enterogenous cysts also have a tendency to become infected, but they remain asymptomatic in the majority of cases.
Rectal Duplication Cysts
Intestinal duplications are rare developmental anomalies, most commonly occurring in females and associated with other congenital defects, especially genitourinary and vertebral anomalies. The diagnosis depends on the fulfillment of three anatomic criteria, namely the cyst must be attached to the alimentary tract, it must be lined by mucous membrane similar to that part of the alimentary tract, and it must possess a smooth muscle coat.
Patients with rectal duplication cysts may be asymptomatic or may present with a perineal mass, constipation, tenesmus, prolapse, lower back pain, urinary symptoms, or recurrent perianal sepsis or fistula formation. Malignant change in a rectal duplication in an adult has been reported but is rare. 11
Tailgut Cysts
These cysts, also called cystic hamartomas, occur predominantly in women and cause symptoms of mass effect or pain in half of patients, 12 which is higher than what is seen with other developmental cysts. These cysts are derived from remnants of the embryonic tailgut and differ from teratomas, which always contain elements of three germ cell layers.
Hjermstad and Helwig 12 collected 53 examples of developmental tailgut cysts in the retrorectal space. The lesions were usually circumscribed, unencapsulated, and multicystic, often filled with a colorless to yellow or gray fluid and had no communication with the rectal lumen. Inflammation occurred in 50% of the patients, one of whom had a poorly differentiated adenocarcinoma.
A 2000 literature review identified 10 cases of malignancy including 6 adenocarcinomas and 4 carcinoids, and also added 5 further cases, 1 of which was a neuroendocrine carcinoma. 13 Complete excision of the multilocular and multicystic process is thus warranted to prevent recurrent draining sinuses and eliminate the possibility of malignant change, which is rare.
16.5.2 Teratoma
These are true neoplasms arising from totipotential cells. Classically, they have representative tissue from each germ cell layer, although the degree of differentiation may vary among the elements. Malignancy tends to arise from one of the germ cells; however, in the anaplastic variety, it may be impossible to distinguish the tissue of origin. The more mature the tissue appears, the more benign the neoplasm tends to be, but all neoplasms should be viewed as potentially malignant.
The malignant potential of sacrococcygeal teratomas varies greatly based on patient age at presentation, with these tumors following a more aggressive course in children, and malignancy being much less common beyond the second decade. 3 , 4 Teratomas tend to be more aggressive when discovered later in childhood. For children, the incidence of malignancy in a 1974 American Academy of Pediatric Surgical Section Survey 14 was only 7% for teratomas present on the first day of life as opposed to 37% for lesions developing at 1 year of age and 50% for those appearing at 2 years of age. Simpson et al 15 reported on 26 sacrococcygeal teratomas in adults. Of these, 21 were benign and 19 occurred in females.
Macroscopic features and the growth pattern of sacrococcygeal teratomas have been described in detail by Pantoja and Rodriguez-Ibanez. 16 The lesions are well encapsulated and may be solid or cystic. They may contain all kinds of tissues, the most prominent ones being respiratory, nervous, and gastrointestinal. Teratomas maintain a strong attachment to the coccyx and sometimes the sacrum, but they rarely adhere to pelvic viscera unless previous inflammation has resulted in secondary adhesions.
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