The bottom line: MRI and CT findings of unusual rectal and perirectal pathology
Although common nonspecific symptoms (i.e., rectal bleeding, pelvic pressure, and change in bowel habits) are associated with rectal cancer, occasionally these are related to a different underlying disease. Over the past few years, considerable progress has been made in imaging of the rectum. Specifically, new magnetic resonance techniques and capabilities provide impressive high-resolution assessment of the rectal wall and enable evaluation and characterization of the perirectal tissues. This paper reviews imaging findings of uncommon causes of rectal and perirectal pathology that may be clinically confounded with rectal cancer. Radiologists need to be aware of uncommon pathologies in this region in order to facilitate optimal management decisions.
KeywordsMR Perirectal mass Presacral mass Rectal mass
Although rectal adenocarcinoma account for the vast majority (98%) of rectal cancers , a wide variety of rectal and perirectal conditions can mimic primary rectal cancer. Over the past few years, significant progress has been made in imaging of the rectum and regional structures. Specifically, new MRI techniques provide impressive high-resolution assessment of the rectal wall and enable evaluation and characterization of the perirectal tissues. The multiplanar capability of MR also helps in lesion localization and characterization.
Unusual rectal and perirectal pathology by location
Gastrointestinal stromal tumor
Retrorectal cystic hamartoma/tailgut cyst
Rectal duplication cyst
Sarcoma (ewing, osteosarcoma, chondrosarcoma)
Benign osseous lesions (giant cell tumor, osteoma, bone cyst)
Colitis cystica profunda
Multicystic benign mesothelioma
There are many types of benign and malignant lesions that can involve the rectal wall and simulate rectal adenocarcinoma as listed in Table 1.
Rectal gastrointestinal stromal tumor
Gastrointestinal stromal tumor (GIST) is the most common mesenchymal neoplasm of the gastrointestinal tract [3, 4]. The most common location for GIST is the stomach (70%) followed by the small bowel (20%–25%). The rectum is the third most commonly involved part of the gastrointestinal tract (5%–7%) [5, 6]. GISTs are thought to derive from a precursor of the interstitial cells of Cajal, normally present in the myenteric plexus, and are clearly distinct from other mesenchymal tumors, such as leiomyomas or leiomyosarcomas . Most can be distinguished histologically by the expression of membrane receptor c-kit. Some authors support stratifying GIST into very low-, low-, intermediate-, and high-risk categories rather than benign or malignant [8, 9]. Most affected individuals are over 50 years of age at time of presentation.
There is no consensus in the literature regarding gender predilection. Although clinical presentation depends on size and site of tumor, abdominal pain or distention is the most common presentation followed by bleeding or unexplained anemia .
The most common sites for metastases are the liver and peritoneal cavity . Unlike gastrointestinal adenocarcinomas, GISTs metastasizing to lymph nodes is extremely rare . Treatment options include surgical excision and c-kit inhibitor therapy.
Large intestine cavernous hemangiomas are rare, but most often involve the rectosigmoid region. Rectal bleeding is the most common clinical presentation. Rectal hemangioma may be a solitary isolated finding or may be associated with Klippel–Trenaunay–Weber syndrome . The presence of phleboliths is a key imaging feature. Calcification of phleboliths is readily apparent on CT imaging. Phleboliths appear as low signal intensity foci on both T1- and T2-weighted images .
Klippel–Trenaunay–Weber syndrome can be diagnosed when at least two of the following features are demonstrated: capillary malformations (usually port-wine stains), soft tissue or bone hypertrophy, and varicose veins or venous malformations . Involvement of the gastrointestinal tract is uncommon, occurring in only 20% of patients . Bleeding is the most common reported symptom in Klippel–Trenaunay–Weber syndrome with gastrointestinal involvement [16, 17]. The distal colon and rectum are the most frequently involved sites [16, 17].
Gastrointestinal carcinoids are currently referred to as gastroenteropancreatic neuroendocrine tumors. The small bowel is the most common location for gastrointestinal carcinoid. The rectum is the second most common site followed by the appendix. Carcinoid of the rectum and appendix are often discovered incidentally and are typically small lesions with a low risk for metastasis . They are epithelial tumors that develop in the deep portions of glands, typically invading through the muscularis mucosa into the submucosa, and resembling submucosal tumors .
In general, the mean age of patients at diagnosis is 56.2 years , and there appears to be no gender predilection. Most patients are asymptomatic at the time of presentation. Although carcinoid syndrome is frequently related to carcinoid tumors, the classic symptoms of flushing, diarrhea, abdominal pain, and occasional asthma or right-sided cardiac valvular problems are actually uncommon. Midgut primary tumors appear to be more hormonally active than distal rectal carcinoids .
Minimally invasive surgery is an option for localized small tumors (< 1 cm). Different treatment strategies are considered when there is evidence of regional invasion or metastatic disease.
Colitis cystica profunda
Colitis cystica profunda can be found anywhere along the gastrointestinal tract, but is most commonly described in the colon. It is an uncommon benign condition characterized by mucin-filled cysts located in the submucosa, frequently associated with solitary ulcer and rectal prolapse syndromes . The etiology remains unclear, but inflammation, mucosal trauma, and rectal prolapse have been suggested. Additional reported associations include ulcerative colitis, Crohn’s disease, adenomatous polyps, Peutz–Jegher syndrome, and spastic colitis . This entity may occur at any age, but is most common in the third and fourth decades . Patients may be asymptomatic or present with symptoms mimicking rectal malignancy, such as rectal bleeding, tenesmus, and diarrhea.
A variety of masses, benign and malignant, can arise from the tissue elements in the mesorectum and presacral space. Contents in this location include osteochondral tissue, neural tissue and soft tissues of the pelvis . Knowledge of specific imaging features can assist in the differential diagnosis. Pathology from adjacent organs in the pelvis can also involve the rectum and potentially simulate a rectal mass. The superior soft tissue contrast of MRI aids in determining the origin of a perirectal mass.
Developmental cysts are the most common congenital entity encountered in the presacral space . They are defined as benign epithelial cysts that are thought to arise from caudal embryonic vestiges . These cysts can be classified as enteric, epidermoid, dermoid, or neurenteric according to the tissue origin and histopathologic features. Developmental cysts are often asymptomatic, but may present with symptoms due to local mass effect such as constipation, rectal fullness, and pelvic pain.
A well-defined, unilocular or multilocular, thin-walled cystic lesion is the main imaging feature . They usually affect middle age women and are often incidentally detected. Complications include rectal bleeding, infection, and recurrent perianal fistulas. In some cases, surgical excision is necessary to confirm diagnosis and prevent complications. Rare malignant transformation to adenocarcinoma, carcinoid, or squamous carcinoma has been reported [5, 31].
Enteric and neurenteric cysts
Enteric cysts are partially or completely lined with intestinal mucosa . There are two types of enteric cysts: the more common tailgut cyst (also known as retrorectal cyst-hamartoma [RRCH] or mucin-secreting cyst) and the more rare rectal duplication cyst (comprises 5% of all duplication cysts) . The tailgut cyst is lined by an assortment of enteric mucosa and lacks a muscle coat; in contrast to the duplication cyst which contains a muscle coat, is lined by rectal mucosa (in addition to possible ectopic mucosa), and is in continuity with the rectum . Neurenteric cysts differ in that they are lined by a mature mucosa of endodermal origin, for instance bladder, and contain a lamina propria .
Epidermoid and dermoid cysts
Focal irregular wall thickening with enhancement in any of the developmental cysts is suggestive of malignant degeneration. Wall thickening with surrounding inflammation is suggestive of superinfection . Clinical history is helpful in distinguishing between the two.
Presacral extramedullary hematopoiesis
It is thought that extramedullary hematopoiesis is a physiologic compensatory phenomenon in the setting of congenital hemoglobinopathies or acquired marrow replacement disorders . It most commonly involves the spleen and liver, and occasionally lymph nodes, as these are hematopoietic organs during embryonic life. Paravertebral and presacral sites are uncommon.
Gynecologic processes can involve the rectum due to their close anatomic relationship.
Deep pelvic endometriosis is defined as subperitoneal invasion of endometrial implants. Commonly involved areas include the posterior-cul-de-sac, uterosacral ligaments, rectum, rectovaginal septum, vagina, and bladder . The rectosigmoid is the segment of bowel most commonly involved . Implants are usually serosal, but can invade deeper with subsequent thickening and fibrosis of the muscularis propria . Adhesions and gastrointestinal obstruction may develop.
Multicystic benign mesothelioma
Mesothelial tumors of the peritoneum include benign adenomatoid tumors, malignant mesothelioma, and cystic mesothelioma (multicystic benign mesothelioma) . The latter is an intermediate-grade neoplasm of the mesothelial cells of the peritoneum . As the name implies, it is a multicystic diffuse lesion involving the peritoneum, omentum, and pelvic abdominal viscera . It is most often seen in women of childbearing age. Cysts are commonly found at sites of prior surgery or pelvic inflammatory disease , and they tend to recur locally. A possible hormonal sensitivity has been suggested since it is most often found in women of childbearing age, and a decrease in cyst size has been shown after treatment with gonadotropin-releasing hormone analog agonist and tamoxifen .
Metastatic disease has a variable appearance depending on the tumor of origin. Metastatic disease of the perirectal region can occur from direct invasion along the peritoneal reflections, intraperitoneal seeding in the pelvis from ascitic fluid, embolic hematogenous spread, and lymphatic extension .
The sacrum forms the posterior border of the pelvis and mass lesions originating from the sacrum can be difficult to separate from the rectum. It is important to assess involvement of the sacrum when evaluating presacral masses. Osteochondral and neurogenic tumors typically remodel or destroy the sacrum .
Sacrococcygeal teratoma is a germ cell tumor containing elements derived from all three germ layers. They arise from cells within the anterior portion of the coccyx . It is the most common presacral tumor in children . Less than 10% are diagnosed in patients > 2 years old, the majority of which are located internally in the abdomen or pelvis and more likely to be malignant .
Chordoma is the most common primary malignant tumor of the sacrum, typically involving the fourth and fifth sacral vertebrae . It arises from the notochord remnants and usually lies in a midline or paramedian location. This lesion affects individuals in a broad age distribution (fourth to seventh decade) with a male-to-female ratio of 2–3:1 . The most common presenting symptom is pain in the lower back or sciatic region, followed by constipation, neurologic compromise, and a sacral or gluteal mass .
Chordomas are generally considered slow-growing lesions, but are locally aggressive. They require radical en bloc resection with wide margins to affect a cure [44, 45]. The use of radiation and chemotherapy for this type of tumor is debatable. Antitumoral activity of monoclonal antibodies may provide improved outcomes for poor surgical candidates and recurrent tumors.
Schwannomas and neurofibromas in the presacral region arise from the lower lumbar and sacral dorsal sensory nerve roots. They are rare, generally benign tumors, but can become very large in size. Neurofibromas have potential for malignant degeneration. Solitary neurofibroma can be indistinguishable from schwannoma based on imaging alone. The presence of multiple nerve sheath tumors suggests neurofibromatosis .
Anterior meningocele is a cerebrospinal fluid (CSF) containing sac that herniates anteriorly through a sacral foramen or sacral defect and may be associated with partial sacral agenesis. Anterior meningoceles are less common than posterior meningoceles, but 80% manifest in the first decade of life . They may be present as asymptomatic or symptomatic pelvic masses, can be quite large, and may be confounded with other cysts in the pelvis . Symptoms are most commonly related to pressure on the adjacent pelvic organs and nerve roots and include dysmenorrhea, constipation, and urinary incontinence . Surgical excision is generally performed as the risk of complication increases with time.
Clinical presentation of rectal and perirectal diseases is often misleading and not necessarily related to rectal adenocarcinoma. Radiologists need to be aware of uncommon pathologies in this region in order to facilitate optimal management decisions.
Compliance with ethical standards
Conflict of interest
None. All authors declare no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
- 31.Dahan H, Arrive L, Wendum D, et al. (2001) Retrorectal developmental cysts in adults: clinical and radiologic-histopathologic review, differential diagnosis, and treatment. Radiographics 21:575–584. https://doi.org/10.1148/radiographics.21.3.g01ma13575 CrossRefPubMedGoogle Scholar
- 41.Diel J, Ortiz O, Losada RA, et al. (2001) The sacrum: pathologic spectrum, multimodality imaging, and subspecialty approach. Radiographics 21:83–104. https://doi.org/10.1148/radiographics.21.1.g01ja0883 CrossRefPubMedGoogle Scholar
- 42.Wells RG, Sty JR (1990) Imaging of sacrococcygeal germ cell tumors. Radiographics 10:701–713. https://doi.org/10.1148/radiographics.10.4.2165626 CrossRefPubMedGoogle Scholar