CARBOHYDRATE MALABSORPTION,
INCLUDING LACTOSE
MALABSORPTION
Carbohydrate malabsorption is a frequent clinical condition caused by fermentation of unabsorbed carbohydrates by colonic flora and giving rise to symptoms. Although lactose is the most commonly malabsorbed sugar, other carbohydrates, including oligosaccharides, disaccharides, and monosaccharides such as fructose, can cause symptoms related to malabsorption.
LYMPHANGIECTASIA AND ABETALIPOPROTEIN
DEFICIENCY
Intestinal lymphangiectasia is an unusual disorder characterized by dilated lymphatic channels in the mucosa, submucosa, or subserosa of the small intestine, leading to protein-losing enteropathy. Waldman originally described an idiopathic form, primary intestinal lymphangiectasia; however, obstruction to the flow of lymph in certain cardiac diseases or hematologic malignant diseases and retroperitoneal lymph node enlargement due to chemotherapeutic, infectious, or toxic agents can secondarily lead to lymphangiectasias that present in the same manner as primary intestinal lymphangiectasia.
CRONKHITE-CANADA SYNDROME
AND OTHER RARE DIARRHEAL
DISORDERS
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Cronkhite-Canada syndrome is a rare, nonfamilial gastrointestinal polyposis syndrome that commonly presents with diarrhea. It is characterized by hyperpig-mentation, hair loss, and dystrophic changes in the fingernails. Individuals of European and Asian descent are most frequently affected, but the syndrome has been reported in all ethnic groups. The cause is not known, but the frequent association with hypothyroidism, systemic lupus erythematosus, rheumatoid arthritis, and scleroderma suggests an autoimmune origin. The syndrome is characterized by development of innumerable polyps throughout the gastrointestinal tract except in the esophagus. The polyps are hamartomas; there is an increased risk of colorectal cancer (25%), however. Patients commonly present with diarrhea and weight loss accompanied by typical dermatologic manifestations that include hyperpigmentation and onychodystrophy. Management is largely supportive, with nutritional support, accompanied by antisecretory and antiinflammatory treatment. Immunosuppressive therapy with glucocorticosteroids and azathioprine has also been reported to ameliorate symptoms, but the duration of treatment is not known.
CROHN DISEASE
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| IMAGING AND REGIONAL VARIATIONS |
In the United States, approximately 1.5 million individuals have Crohn disease. Crohn disease is one disease in a larger group of inflammatory bowel disorders, which includes ulcerative colitis, indeterminate colitis, and microscopic colitis. Crohn disease is a progressive illness characterized by transmural inflammation within the digestive tract that may occur anywhere from mouth to anus. Skip lesions of normal and inflamed, “cobblestoned” mucosa describe its classic luminal appearance. The phenotype is characterized by the disease’s severity, site, and type of manifestation, whether inflammatory, fibrostenotic, or fistulizing.
TYPHOID FEVER
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| TYPHOID FEVER: TRANSMISSION AND PATHOLOGIC LESIONS |
In popular culture, the potential devastation of typhoid fever has been best illustrated by the story of Typhoid Mary, also known as Mary Mallon, the personal chef to numerous affluent families in the greater New York City area in the early 20th century. She was an asymptomatic chronic carrier of the Salmonella enterica serotype typhi (previously, S. typhi) and caused approximately 50 deaths as she moved between families, rejecting the notion that she had a role in their demise. She spent the bulk of her last 30 years of life in and out of quarantine.
INFECTIOUS ENTERITIS
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| VIRAL ENTERITIS |
Infectious enteritis is a common worldwide illness with a multitude of underlying pathogens at play. The majority of infectious diarrheal diseases are acute in onset duration (< 2 weeks). Globally, acute enteritis is the fifth leading cause of death across all ages. Innumerable studies demonstrate that approximately 70% to 75% of acute diarrhea cases are viral in cause. Previously, culture techniques could not isolate most bacteria. With the advent of deep 16S ribosomal polymerase chain reaction sequencing techniques, genetic signatures can now identify bacteria, so it is not necessary to rely on tedious culture techniques. These technologies have isolated a bacterial source in approximately 15% of acute enteritis cases. Protozoal organisms are responsible for a lesser fraction of these cases.
HIV/AIDS Enteropathy
Up to 50% of HIV patients in the United States report diarrhea, but a distinct cause is identified in only 60% to 70% of these cases. HIV enteropathy is characterized by chronic diarrhea lasting more than 4 weeks and accompanied by malabsorption and abdominal discomfort. As is characteristic of small bowel diarrhea, stools are typically voluminous and may occur postprandially. There may be marked electrolyte disturbances, severe dehydration, and unintentional weight loss.
ANOMALIES OF THE VENTRICULAR SEPTUM
Ventricular Septal Defects (“MEMBRANOUS”)
Of the anomalies involving ventricular septal defects, those located beneath the aortic valve, the membranous ventricular septal defects, are by far the most common. Not only are these defects frequently seen in association with other cardiac anomalies, but even when occurring as isolated lesions, the membranous VSDs constitute the most important and also the most common type of congenital heart disease. This is not surprising considering the complex embryologic history of the subaortic portion of the ventricular septum. This is the last part of the septum to close, a closure effected by the fusion of components from the embryonic muscular septum, endocardial cushions, and conal swellings. Anomalous development of any one or several of these contributors will lead to a defect of the ventricular septum. There fore, although located in the same general area, membranous VSDs may vary considerably in position and size. Some are found immediately beneath the right and posterior aortic valve cusps; these probably are caused mainly by deficiency of the conus septum and, because of a lack of support for the aortic valve cusps, may lead to prolapse of one or both cusps, causing aortic regurgitation. Other membranous VSDs mainly caused by deficiency of the right limb of the endocardial cushions, or failure of otherwise normally developed endocardial cushions to fuse with the ventricular septum and conus septum, are located a few millimeters away from the aortic valve, leaving a rim of muscular or fibrous tissue. All these defects are located in the general area where the membranous septum is found in the normal heart, and thus are usually rather loosely referred to as “membranous septal defects.”
ANOMALIES OF
TRICUSPID VALVE
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| TRICUSPID ATRESIA |
Of the congenital tricuspid valve anomalies, only two tricuspid valve atresia and Ebstein’s anomaly are clinically significant. Tricuspid regurgitation and stenosis occurring as isolated lesions are extremely rare. Some forms of septal defects, such as endocardial cushion defects or ventricular septal defects, may involve the tricuspid valve’s medial cusp, rendering this cusp insufficient or allowing for a direct shunt from the left ventricle to the right atrium. Tricuspid valve stenosis usually accompanies pulmonary atresia or severe stenosis when the ventricular septum is intact. Actually, the tricuspid valve in these patients, although small and often with thickened cusps, is normally formed, and the stenosis is a secondary hypoplasia.
