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Evaluation of diffuse parenchymal disease is subjective and can be difficult for the novice sonographer. Echogenicity of the spleen is assessed by comparing splenic parenchyma to the adjacent liver and left renal (kidney) cortex as described above. Changes in echogenicity can be seen with extramedullary hematopoiesis, passive congestion, nodular hyperplasia, inflammation, infection, neoplasia, and splenic torsion.

 Extramedullary hematopoiesis. Generally associated with mildly reduced echogenicity (hypoechoic).

 Passive splenic congestion. Generally associated with hypoechoic changes in acute phases but may be associated with hyperechoic changes in more chronic processes. Architecture is rarely disrupted.

 Nodular hyperplasia. May be associated with either hypoechoic or hyperechoic changes which are relatively mild. The splenic capsule may be mildly irregular as described above. Nodular hyperplasia is a benign condition commonly seen in older dogs (see Figure 9.8C,D).

 Inflammatory or infectious diseases (fungal, bacterial, rickettsial). Generally these conditions cause mild to moderate splenomegaly with diffuse hypoechogenicity. With acute inflammation or infection, the changes are more pronounced with more prominent hypoechogenicity and a finely mottled appearance (see Figures 9.7 and 9.9A,B).

 Neoplastic conditions. Lymphosarcoma, mast cell tumor, and other myeloproliferative diseases generally produce an appearance of generalized coarse mottling referred to as a “honeycomb”, “moth‐eaten” or “Swiss cheese” appearance (Nyland et al. 2002) (compare Figure 9.14 to Figures 9.6 and 9.8A,B). It is important to remember that both lymphosarcoma and mast cell tumor can also be present with very mild diffuse changes and the spleen may even have a normal appearance. As a result, fine needle biopsies of the spleen may be indicated even in the absence of sonographic abnormalities.

 Splenic torsion. Marked splenomegaly with a diffusely hypoechoic to anechoic lacy appearance (compared to the hyperechoic [brighter] lacy appearance seen with LSA of the parenchyma) is typical of splenic torsion (Figure 9.15). If color flow Doppler is available, then absence of blood flow in the splenic vein is consistent with torsion. Thrombus formation may also be identified within the splenic vein in some cases of splenic torsion. Additionally, a perivenous hyperechoic triangle at the level of the splenic hilus has been described as a common feature in dogs with splenic torsions (Mai 2006; Hecht 2008).

Figure 9.15. Splenic torsion parenchymal lesion. (A) Note the hypoechoic (dark) lacy appearance to the spleen (SP) shown adjacent to the left kidney (LK). (B) Another view of the same spleen in (A) showing its thickness and its hypoechoic (dark) lacy parenchymal appearance. Compare to the hyperechoic (bright) lacy appearance of splenic lymphosarcoma in Figure 9.14. The perihilar region is hyperechoic (bright) without clear imaging of the hyperechoic triangle shown in Figure 9.16. Color flow Doppler was helpful in this case (not shown) documenting the lack of perihilar blood flow.

Figure 9.16. Splenic torsion vascular lesion. (A) Image of the splenic hilus in a dog with splenic torsion. Note the hyperechoic triangular region around the vessel, continuous with the hyperechoic and hyperattenuating mesenteric fat. (B) Image of the splenic hilus in another dog with splenic torsion. There is a hyperechoic triangular region around the splenic veins, continuous with the mesenteric fat, which is markedly hyperechoic and hyperattenuating. There are also intraluminal echoes in the splenic veins consistent with thrombosis. Both (A) and (B) show the perivenous hyperechoic triangle supportive of splenic torsion.

Source: (A) and (B) reproduced with permission from Mai (2006).