Dermoid and epidermoid cysts

Dermoid and epidermoid cysts (Fig. 29.1a) are typically benign and are frequently observed in women aged 40–50 years. The main risk is infection (30%) and can then be difficult to distinguish from peri rectal abscess. Epidermoid and dermoid cysts tend to be well circumscribed, with a thin outer layer. They contain stratified squamous cells and skin appendages [8, 11]. Unlike tailgut cysts, they do not contain transitional or glandular epithelium. They are usually unilocular, filled with a clear liquid.

Enteroid (tailgut) cysts

Retrorectal hamartomas (tailgut cysts) or mucoepidermoid cysts (Fig. 29.2) are the most common cysts derived from endoderm and mesoderm. They are embryonic remnants of the terminal portion of the primitive hindgut, located after the cloacal membrane (tailgut). The distal portion of the primitive hindgut is temporary and should fully regress at the seventh week of gestation. Failure to regress is one origin of tailgut cysts. The second possible source of a hamartoma is persistence of the neurenteric canal, which is formed from the union of the endoderm and mesoderm. This canal is formed the 19th day of gestation and is obliterated when the caudal part of the notochord is completely formed. Persistence of this canal can be observed above the S2–S3 vertebrae in adults and may be the source of a congenital cyst. Histologically, the wall of these cysts can form from one or multiple types of epithelium normally found in the gastrointestinal tract of adults and fetuses [8]. These cysts are defined by the presence of at least transitional cells or cylindrical epithelium. Squamous epithelium is present in 75 % of cases, possibly as a result of metaplasia induced by inflammation [10, 11].

Enteric cysts occur predominantly in middle-aged woman and present with pain (often during defecation) or symptoms related to a mass in 50 % of cases. Rectal exam may identify an extrinsic mobile or fixed fluctuating lesion. The location is predominantly in retrorectal space, although tailgut cysts have been described in the perianal space, the buttocks, the postsacral space, and even anterior to the rectum. Macroscopically, most have multicystic locules (80 %) and are well circumscribed but unencapsulated, usually starting in the retrorectal space. They rarely reach the rectal wall. The cysts can contain amorphous debris, keratin, or mucus (in the presence of mucus-secreting cells). Unlike teratomas, no calcifications are found. Inflammation is often present, whether acute or chronic (especially after trauma with cyst rupture), but it does not correlate with clinical symptoms. Malignancy is possible, in the form of adenocarcinoma or squamous cell carcinoma (occurs in 7 % of enteric cysts) [7]. Various findings are usually seen on magnetic resonance imaging (MRI):

Tailgut cysts differ from duplication cysts in that they do not have a well-defined muscular wall, myenteric plexus, or serosa, although smooth muscle fibers can be found in a single layer.

Duplication cysts can occur throughout the digestive tract, with a predilection for the small bowel. Cystic rectal duplication represents 5 % of all developmental cysts. They occur solely or in combination with different abnormalities (lumbosacral, urogenital, and/or digestive). They can present either as a cyst (90–95 %) or a secondary bowel parallel to the normal digestive tract. Only the mesenteric edge of the duplication is in close contact with the main digestive wall. In 80 % of cases, however, the lumen does not communicate with the primary gastrointestinal tract (noncommunicating duplications). Retrorectal duplication cysts are usually not communicating. They must have two smooth muscular layers and a mucosa that is similar to the rectal mucosa, and they sometimes contain ectopic tissue (e.g., gastric mucosa in 25 %, pancreatic tissue). Malignant transformation has been described [8].

Teratomas

Teratomas are the most common tumors in children. These are diagnosed in half of cases during the antenatal period using ultrasonography. Teratomas are characterized by a combination of differentiated tissues derived from the three germ layers: ectoderm (squamous and pilosebaceous annexes, brain and nervous tissue, glia, retina, and choroid plexus ganglion), endoderm (mucous, gastrointestinal, and lung, thyroid, salivary glands), and mesoderm (bone, cartilage, smooth muscle, fibrous and fatty tissue) [8, 12, 13]. They can become malignant (10 %), forming teratocarcinomas, choriocarcinomas, and dysgerminomas [14].

Chordoma

Chordomas are the most common malignancies of the retrorectal space [1, 15–18]. They develop from embryonic remnants of the notochord. Fifty to 60 % of chordomas are located in the sacrococcygeal region, but they can be located all along the spine. These tumors are rare (2–4 % of malignant bone tumors), frequently diagnosed in patients between 40 and 70 years old, and are more common among males (male-to-female ratio, 2:1). These tumors have a low possibility for malignancy, with approximately 20 % metastatic risk, but they can be very aggressive locally. They grow slowly and often are fortuitously discovered during a routine rectal or pelvic exam. Chordomas are lobulated gelatinous masses that invade and destroy adjacent bone structures, requiring radical resection to prevent recurrence. Computed tomography (CT) can show a large osteolytic soft-tissue mass in the sacrum and allow evaluation of the locoregional invasion. MRI characterizes this tumor with a hypo signal or intermediate signal in T1 and an hypersignal in Fig. 29.3. Enhancement of the tissue component varies but is often moderate. Their prognosis is poor, and important sequelae occur after surgical resection according to the level of the bone and sacral nerve resection.

Meningocele

Meningoceles are rare, sporadic, and more common in women than men. The anterior sacral meningocele is the result of a herniated dural sac in the presacral space, caused by a bony defect of the anterior wall of the sacrum. The sac communicates with the spinal canal and is filled with cerebrospinal fluid. Patients can present with headache exacerbated by defecation, urinary symptoms, constipation, sacral pain, and sometimes meningitis. Other bone defects occur in 50 % of cases. CT reveals a well-circumscribed tumor and a watery, uniform cyst and confirms the bone defect.