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PEER REVIEWED 92 IMAGING ESSENTIALS Concurrent anechoic peritoneal effusion may be present due to hypoproteinemia secondary to protein- losing enteropathy. Duodenal and Jejunal Wall Thickening Focal wall thickening with a loss of wall layering are commonly seen with intestinal focal neoplasia ( FIGURE 18 ). 14,35,45,46 The most common intestinal tumors of dogs are leiomyosarcoma, lymphoma, and adenocarcinoma. 47-50 Smooth muscle tumors of the intestines, such as leiomyosarcoma, often appear as large masses, eccentrically projecting from the intestinal wall, containing single or multiple hypo- or anechoic regions. 50 Carcinoma is a localized, irregular, often mixed echogenicity thickening of bowel wall with a loss of layering; 51 it can also present as an annular, constrictive lesion ( FIGURE 19 ) that might be difficult to see on ultrasound, due to the gravel sign surrounding the area caused by the chronic partial obstruction. Although more common in the large intestine, gastrointestinal stromal tumors can also be seen in the small intestine. 52 No unique features of gastrointestinal stromal tumors have been recorded to differentiate from other gastrointestinal spindle cell tumors. 52 FIGURE 19. Longitudinal axis view of a segment of jejunum of a dog diagnosed with cytologically confirmed carcinoma. Note the irregularly marginated, heterogeneous thickening of the jejunum ( calipers ), and the eccentric, irregularly shaped, heterogeneous mass (). This eccentrically located mass causes constriction of the lumen; the hyperechoic lumen can be identified orad (proximal) to the lesion but disappears aborad (distal) to the level of the mass. FIGURE 20. Transverse axis view of a segment of jejunum of a cat diagnosed with multicentric lymphoma. Note the severe jejunal wall thickening ( calipers ), measuring 0.5 cm, and the severely thickened muscularis layer (). The lumen of this segment of jejunum contains gas and echogenic fluid. FIGURE 21. Transverse axis view of a segment of jejunum (A) and longitudinal axis view of the right colic lymph node (B) of a cat diagnosed with cytologically confirmed, multicentric lymphoma. Note the hypoechoic mass with complete loss of wall layering circumferentially surrounding the segment of jejunum that measures 0.78 cm in wall thickness. The hyperechoic mucosal-luminal interface within the center of this mass demarcates the gas within the small intestinal lumen. The right colic lymph nodes are rounded, hypoechoic, and severely enlarged, measuring up to 0.8 cm in thickness. A B