Fig. 16.2 (A, B) Normal jejunal villi: jejunal biopsy (AFIP 68-992) and endoscopic view (AFIP 68-990). (C,D) Tropical sprue, mild: jejunal biopsy (AFIP 68-1052) and endoscopic view (AFIP 68-1083-3). (E,F) Tropical sprue, moderate: jejunal biopsy (AFIP 68-1036) and endoscopic view (AFIP 68-1086-2). (G,H) Tropical sprue, severe: jejunal biopsy (AFIP 68-1042) and endoscopic view (AFIP 68-1080-1).

Etiology and Pathology

Histological Findings

A. Bone marrow: In early stages, there is megaloblastic hyperplasia. In late stages, there is hypoplasia.

B. Small bowel (jejunal biopsy) (Figs. 16.2 and 16.3):

1. The finger-like villi in the mucosa become broader and shorter and have a ridge-like pattern. There is partial to subtotal villous atrophy (subtotal only in a small percentage) plus crypt hyperplasia.

2. The columnar brush border epithelium normally present on the surface and tips of the villi (which is replaced every 2 days by migration of the cuboidal surface epithelium from the crypts of Lieberkühn and has a high absorptive power) fails to develop into mature columnar cells. The nuclei of the surface epithelial cells do not mature but instead remain large and eccentric in position. There is vacuolization within the cells.

3. Thickening of the basement membrane beneath the epithelial cells and demonstration of lipid deposition by oil red O stain is not pathognomonic but is a helpful finding on biopsy of tropical sprue.

4. There is an increase in the number of goblet cells.

5. The lamina propria may show chronic mononuclear cell infiltrate and a varying degree of edema; later there is atrophy.

6. All layers of the small bowel may become atrophic and thin, including the tunica submucosa and tunica muscularis. The atrophic process affects the filiform papillae of the tongue as well as the mucosa of the entire gastrointestinal tract.

7. There is a varying degree of damage and disruption of the vascular network to the villi and mucosa. The loss of the surface epithelium may be influenced by this factor.

Fig. 16.3 Tropical sprue-jejunal biopsy before (A) and after (B) therapy. AFIP 68-995-1. Endoscopic view before (C) and after (D) therapy. AFIP 68-995-2.