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The identification of nodules or mass lesions within the splenic parenchyma is the most basic of the four features of the POCUS spleen (size, echogenicity, nodules, vasculature). It is important to recognize, however, that ultrasound does not allow differentiation between benign and malignant processes, unless advanced contrast‐enhanced ultrasound studies are performed (limited availability) that still may not prove helpful (Fife et al. 2004; Rossi et al. 2008). The sonographer should keep in mind that according to one study, benign splenic masses are more common than malignant splenic masses in dogs (Fife et al. 2004).

 Nodular hyperplasia. Nodules associated with nodular hyperplasia or extramedullary hematopoiesis may be variable in echogenicity (hyperechoic, hypoechoic, isoechoic or mixed echogenicity) when compared to normal splenic parenchyma (Figure 9.10A,B). In addition, nodular hyperplasia may be associated with a mildly irregular splenic capsule without associated nodular lesions. This change is commonly seen in older dogs.

Figure 9.6. Splenomegaly with spleen extending to urinary bladder. This severely enlarged spleen extends caudally to the fluid‐filled (anechoic) urinary bladder. Although it appears relatively normal regarding its echotexture and echogenicity, this dog had splenic lymphosarcoma diagnosed by percutaneous needle biopsy. Compare to Figure 9.14 showing the ultrasonographic variability of splenic lymphosarcoma (LSA).

Figure 9.7. Splenomegaly with normal echogenicity. Infectious diseases can cause splenomegaly with variable changes in echogenicity. Shown here is an image from a dog with ehrlichiosis.

Pearl: In cases with nodular lesions, it may be difficult to differentiate changes associated with nodular hyperplasia from other processes without further testing (cytology or histopathology).

 Myelolipoma. Myelolipomas are incidental findings in older dogs and are identified as discrete, strongly hyperechoic (bright) and frequently irregularly shaped nodules most often located near the hilus or associated with the parenchymal vessels. Less commonly, they are smooth in shape and buried within the splenic parenchyma. They are generally small in size but are occasionally quite large and can also be seen in cats. Myelolipomas are typically of no clinical consequence (incidental finding) (see Figure 9.10C,D).

 Hematoma. Abdominal trauma may be associated with hematomas and splenic parenchymal injury (Figure 9.11). Hematomas (benign masses) may be variable in appearance but initially are generally anechoic to hypoechoic (darker) when compared to normal splenic parenchyma. As the blood within the hematoma forms a clot, the lesion may become more isoechoic or hyperechoic to normal parenchyma. As the clot retracts, the lesion may again become hypoechoic. Anechoic fluid may form around the clot and appear as a cyst‐like lesion. These factors may make hematomas difficult to distinguish from other mass lesions, including neoplasia.

Pearl: Fine needle biopsy of hematomas generally yields nonspecific cytological results and therefore the absence of neoplastic cells on cytology does not rule out neoplasia. A more definitive diagnosis of hematoma is obtained by splenectomy and histopathological evaluation; however, even this may be complicated by a large hematoma associated with a smaller malignant mass, resulting in a possible misdiagnosis.

 Abscess. Splenic abscesses are uncommon and usually cannot be distinguished from other processes that produce nodular or mass lesions. The appearance may be variable with well‐defined or indistinct margins and variable echogenicity. Abscesses most commonly appear as hypoechoic lesions, which may have cystic components or mixed echogenicity. A more conclusive finding for an abscess (in contrast to neoplastic processes) is the presence of gas (due to gas‐forming bacteria) within the lesion. This appears as focal areas of hyperechogenicity with distal edge shadowing (see Chapter 3).

Figure 9.8. Splenomegaly with splenic hyperechogenicity (brighter than normal) and hypoechogenicity (darker than normal). (A) Relatively normal homogeneous echotexture in a hyperechoic (brighter than the liver) spleen. The diagnosis by percutaneous needle biopsy was lymphosarcoma (LSA). (B) Another relatively unremarkable hyperechoic spleen in a cat diagnosed with splenic LSA by percutaneous needle biopsy. Note an anechoic triangle of free fluid (Fluid). (C,D) Mottled echotexture with hypoechogenicity (darker) in spleens representing nodular hyperplasia diagnosed by percutaneous needle biopsy.

Pearl: Fine needle aspiration/needle biopsy with cytology and bacterial culture and sensitivity is helpful in confirming a splenic abscess diagnosis. Be aware that necrotic centers of neoplastic lesions can be mistaken for abscesses, and so diagnosis should always be in conjunction with clinical findings and in some cases a definitive diagnosis may only be gained with splenectomy and histopathological evaluation.