A 60-year-old woman comes to the office with persistent, profuse mucoid diarrhea. Despite not eating much for the past 2 days, her diarrhea has not decreased, but she has no other symptoms. The patient has not had age-appropriate colon cancer screening. Family history is unremarkable. She does not use tobacco, alcohol, or illicit drugs. Vital signs and cardiopulmonary examination are normal. The abdomen is soft and nondistended. There is no hepatosplenomegaly. Laboratory studies show hypokalemia and microcytic anemia. Colonoscopy reveals a 2.5-cm, cauliflower-like mass in the sigmoid colon. The mass is resected and the histopathology of the lesion is shown in the exhibit. Which of the following is the most likely diagnosis in this patient?

Question

A 60-year-old woman comes to the office with persistent, profuse mucoid diarrhea.  Despite not eating much for the past 2 days, her diarrhea has not decreased, but she has no other symptoms.  The patient has not had age-appropriate colon cancer screening.  Family history is unremarkable.  She does not use tobacco, alcohol, or illicit drugs.  Vital signs and cardiopulmonary examination are normal.  The abdomen is soft and nondistended.  There is no hepatosplenomegaly.  Laboratory studies show hypokalemia and microcytic anemia.  Colonoscopy reveals a 2.5-cm, cauliflower-like mass in the sigmoid colon.  The mass is resected and the histopathology of the lesion is shown in the exhibit.  Which of the following is the most likely diagnosis in this patient?

Quizplus · Accepted Answer

11ec160b_3939_e795_9249_81e4c2b01995_MD0001_00 Biopsy of this patient's mass demonstrates long glands with finger-like (villous) projections extending from the surface as well as dysplastic epithelium, which are characteristic of a villous adenoma. A villous adenoma is often large and sessile and can have velvety or cauliflower-like projections. By contrast, a tubular adenoma is composed of dysplastic colonic mucosal cells that form tube-shaped glands and tends to be smaller and pedunculated. A mixture of these 2 types indicates a tubulovillous adenoma. Of these, villous adenomas are the most likely to undergo malignant transformation. Adenomas in the colon can cause occult or visible bleeding, leading to iron-deficiency anemia. Large polyps may occasionally cause partial obstruction with pain, constipation, and abdominal distension. In addition, villous adenomas can produce large quantities of prostaglandin E2, which results in increased mucin production and a secretory diarrhea characterized by watery, mucinous stools. Mucin is a potassium-rich glycoprotein; excessive production can result in hypoproteinemia and hypokalemia. (Choice A) Intestinal carcinoids can cause diarrhea and are often associated with additional symptoms such as flushing, wheezing, and vascular telangiectasia when they metastasize. Histopathology is typified by insular (nesting) masses of small, round cells with peripheral palisading, granular cytoplasm, small nucleoli, and salt-and-pepper chromatin. (Choice B) Hamartomatous polyps consist of disorganized mucosal glands, smooth muscle, and connective tissue. They may occur sporadically or in Peutz-Jeghers syndrome or juvenile polyposis. These polyps can cause bleeding and intussusception, but not secretory diarrhea. (Choice C) Hyperplastic polyps are characterized by a proliferation of nondysplastic epithelial cells resulting in a serrated or "sawtoothed" architecture seen in the upper parts of the crypts. They are typically small lesions and almost always asymptomatic. (Choice D) Signet ring cell carcinoma can occur in different locations, such as the stomach, breast, ovary, and colorectal area. Tumor cells contain abundant mucins that push the nuclei to the periphery and give the tumor cells their characteristic appearance. Educational objective: Adenomatous polyps are either tubular, villous, or tubulovillous, depending on their histologic appearance. Villous adenomas tend to be larger, sessile, and more severely dysplastic than tubular adenomas. Villous adenomas can cause a secretory diarrhea from increased mucin production; patients may develop hypoproteinemia and hypokalemia.

A 60-Year-Old Woman Comes to the Office with Persistent, Profuse