Carcinoembryonic Antigen Elevation Due to Bowel Sequestration With Mucocele Formation Following Colonic Resection Open Access

Carcinoembryonic antigen (CEA) is a serologic test recommended as a marker of colorectal carcinoma recurrence. A CEA level may be elevated as a result of benign disease, such a pelvic inflammatory disease, as well as a variety of malignancies. No literature of CEA elevations associated with colonic mucocele exists.

The patient was a 73-year-old man who was found to have blood in his stool in 1995. Colonoscopic examination revealed a mass lesion in the sigmoid colon, at 20 cm, which on biopsy was diagnosed as a well-differentiated adenocarcinoma. Resection of a 34-cm segment of left colon was performed with primary end-to-end anastomosis using double-line staple sutures. Examination of the resected colon revealed an exophytic centrally ulcerated tumor measuring 4.5 cm in diameter and occupying approximately 60% of the luminal diameter. The lesion was located 3 cm from the distal margin and 26 cm from the proximal margin of excision. On microscopic exam, a well-differentiated adenocarcinoma without mucinous component was seen extending into the muscularis propria (Figure 1). The remainder of the mucosal surface appeared unremarkable. A solitary pericolic lymph node examined was negative for metastases. No distant metastases were seen on computed tomographic examination of the abdomen. The patient was classified as stage I (T2, N0, M0) and received no adjuvant therapy.

At follow-up visit 6 years later, an elevation of the CEA level was noted with maximum elevation of 7 ng/mL. Subsequent computed tomographic scans revealed the presence of a 2.5 × 3.0-cm parasigmoid, lobulated, cystic mass (Figure 2). The positron emission tomographic (PET) scan demonstrated extremely intense increased activity in the region of the patient's parasigmoid mass (Figure 3). At exploratory laparotomy, a cystic dilation of the wall at the site of the anastomosis, with small grapelike protrusions on the serosal surface, was seen. A 16-cm segment of bowel including the anastomotic site and mural mass was resected and submitted for intraoperative consultation. Examination of the remainder of the abdomen showed no evidence of disease. A week postoperatively, the serum CEA level had decreased to 3.5 ng/mL.

The serosal aspect of the resected bowel was largely unremarkable except for an area of adhesed fat 2.5 cm from one end overlying a palpable mass. On sagittal section this mass was seen to be a unilocular cystic cavity measuring 5.5 × 3.5 × 1.3 cm and containing viscous mucus (Figure 4). Mucin was not limited to the cyst but was also seen within the subserosal fat. Touch preparation was performed. The mucin appeared to be acellular, and a diagnosis of “mucinous lesion present” was rendered. Inspection of the mucosal surface of the bowel showed scarring at the anastomotic site, with no defect or communication with the underlying mural cyst. No polyps, masses, friability, or other irregularities were present. In addition, no diverticular orifices were identified.

On microscopic examination, the wall of the cyst was found to be lined by full-thickness bowel wall with atrophy and fibrosis of the muscularis propria (Figure 5, a and b). In some areas the mucosa lining the cyst had a slightly villiform appearance (Figure 6, a), whereas elsewhere it was flattened and simplified. The epithelium showed reactive epithelial changes with a mildly increased nuclear to cytoplasmic ratio but showed no dysplasia. Immunohistochemical stains performed on paraffin sections including p53 and MIB-1 demonstrated this epithelium did not react with p53, and the proliferative zone was confined to the crypts, which is consistent with a nonneoplastic epithelium. Within the surrounding subserosal tissue, acellular mucin pools were present (Figure 6, b). There was no evidence of adenocarcinoma anywhere within the resection.

The findings in this case are sequestration of the bowel following a left colon resection and primary colo-colic anastomosis with subsequent development of a mucocele in the sequestered segment and mild elevation of CEA. To our knowledge, this is the first report describing an elevation of CEA due to sequestration with mucocele formation following colon surgery, as a Medline search fails to reveal any previously reported cases.

The differential diagnosis for this lesion included a diverticulum, a congenital defect, and recurrent carcinoma. The presence of all layers of the bowel wall in the cystic mass precludes this from being a preexisting diverticulum. The common diverticula in the colon are pseudo-diverticula resulting from the herniation of mucosa in areas in which vessels traverse the wall. These pseudo-diverticuli do not contain submucosa and muscularis propria. In contrast, the cyst wall seen in this case contained all the layers of the bowel wall, akin to true diverticulum, such as a Meckel diverticulum. However, unlike true diverticulum, this sequestered segment showed no communication with the bowel lumen. Neither pulsion, which is an outpouching due to excessive mural pressure or traction (pulling of the wall due to mural fibrous adhesions) would result in this type of sequestration. A preexisting congenital colonic duplication or cyst seems highly improbable, particularly as previous exploration and resection had been performed with no such anomaly noted. Finally, there is no evidence of neoplasia, suggesting carcinoma recurrence. In this setting, the sequestration of the segment must be a result of surgical manipulation at the time of the initial colectomy.

Sequestration is an unusual complication of colorectal surgery. However, it is possible that it may occur simply as a result of oversewing a bowel segment at the time of anastomosis. This may not be frequently reported, as it likely has no clinical consequences in most situations.

The development of a mucocele in this sequestered segment is similar to the rarely reported finding of colonic mucocele developing in segments of colon with distal obstruction. The colonic epithelium has the capacity to secrete mucin; however, usually it fails to accumulate it, and it is excreted instead. Mucocele development occurs either when distal obstruction interferes with excretion, when isolation of the segment interrupts normal continuity of flow, or when excessive production in a confined segment (such as that seen in the appendix) occurs.1–4 

Of interest is the mild elevation in the CEA level seen with subsequent decline to normal range postoperatively. CEA is considered an effective means for monitoring recurrence of disease in colorectal cancer patients. However, CEA is not 100% specific for colorectal carcinoma, and elevation of this marker has been noted in a variety of settings, including benign conditions and multiple types of malignancies.5 In this case, the elevation appears to be a product of the mucocele, based on the fact that the elevation prompted the discovery of the lesion and resection of the lesion resulted in decrease of CEA level. Previously CEA has been reported within oral mucocele epithelium as detected by immunohistochemical technique.6 

In concert with the elevated CEA, clinical suspicion of recurrent disease was based on radiologic findings. A CT scan showed a cystic mass. The PET scan was interpreted at that time as showing increased activity in the mass. In retrospect, increased activity on the PET scan was not unequivocally related to the mass lesion. PET positivity may have represented normal uptake in the bladder rather than increased activity in the mass lesion, as originally interpreted. Alternatively, the PET positive signal may have demonstrated increased uptake in the mucocele.

In conclusion, sequestration of the bowel wall following colorectal surgery may result in a mucocele and mild elevation of CEA that can be mistaken for recurrent carcinoma. Gross examination of the lesion may be confusing in the setting of mucin extravasation, mimicking the findings seen in mucinous adenocarcinoma. The correct diagnosis can be made if attention is paid to the presence of all layers of the bowel wall in the sequestered segment as well as the presence of lamina propria associated with the nonneoplastic colonic epithelium lining the lumen of the sequestered segment.