(A–C) Examples of nodular hyperplasia characterized by homogeneous echogenicity of the mass which may be hyper‐ or hypoechoic relative to the adjacent splenic parenchyma. Importantly, note that in contrast to fluid‐filled structures that have acoustic shadowing artifact extending through their far‐field, these solid nodules do not. Also, in the distal field is a transverse image of normal small bowel that appears like a “hamburger” (colored cartoon to the lower right of the small bowel). (D) An example of a myelolipoma, a common incidental finding in older dogs, often hyperechoic (bright) discreet nodules located near the splenic hilus but may also be located parenchymally.Figure 9.11. Splenic hematomas and infarcts. (A) The spleen has a hypoechoic (dark) area within its parenchyma that represents an acute hematoma in a young dog that had just incurred blunt automobile trauma. The splenic finding was observed during an AFAST exam. (B) The spleen has a hypoechoic area within its parenchyma that represents an infarcted region seen in a bluntly traumatized puppy.Source: (B) courtesy of Dr Autumn Davidson and Tomas Baker, University of California, Davis, CA.Figure 9.12. Splenic hemangiosarcoma (HSA) and its variability. (A) A splenic mass that was diagnosed as HSA by splenectomy and histopathological evaluation. Note normal spleen in the upper left image is confluent with the mass of mixed echogenicity determining its splenic origin. (B,C) Typical mass appearances of splenic HSA. For positive splenic identification, the mass should be traced into obvious splenic parenchyma. Surprisingly, in some cases, HSA and other splenic masses can mimic the less common benign diagnosis of splenic abscess. A large splenic mass of mixed echogenicity or with a necrotic center may also mimic free fluid when depth is inadequate (too zoomed in or the depth set too shallow) or the mass is excessively large (exceeding the depth limits of your ultrasound machine). (D) An example of HSA that is more infiltrative and less mass‐like. Note that despite the mixed echogenicity, the spleen has little to no deformation of its normal contour.
Lymphosarcoma (LSA) has a variable appearance when associated with the spleen. LSA may appear as a focal mass lesion, multifocal mass lesions, or as diffuse parenchymal disease referred to as a “honeycomb,” “moth‐eaten” or “Swiss cheese” appearance (Figure 9.14) (Nyland et al. 2002). Mass lesions due to LSA are generally hypoechoic with indistinct margins and may be singular or multifocal in nature. However, they can also be isoechoic or slightly hyperechoic to normal splenic parenchyma, and may or may not distort the splenic contour (see Figures 9.6 and 9.8A,B).
Figure 9.13. Target lesion. Target lesions suggest metastatic neoplasia and should trigger a search for a primary tumor as well as other sites of metastasis, and the Global FAST approach serves as a rapid screening staging test.
Figure 9.14. Lymphosarcoma (LSA). The “Swiss cheese” or “moth‐eaten” appearance of the spleen is often caused by LSA. However, LSA has variable presentations including a diffuse homogeneous echogenicity change that is hyper‐or hypoechoic. Moreover, splenic LSA may appear ultrasonographically unremarkable. Compare to Figure 9.6 showing the variability of splenic LSA and Figure 9.16 showing the lacy appearance of splenic torsion.
Pearl: Diagnosis of all presentations of lymphosarcoma may be made via percutaneous needle biopsy (Crabtree et al. 2010).
Other tumors may have similar variability in size, echogenicity, and the ability to distort the splenic contour. Therefore, it is always important to base a diagnosis on other clinical findings as well as cytological and histopathological evaluation.
Echogenicity and Parenchymal Conditions
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
