Evaluation of splenomegaly is a subjective assessment in dogs unless splenic enlargement is severe.

       Splenomegaly in cats is almost always due to pathology and warrants additional evaluation.

       Nodular and mass lesions within the splenic parenchyma are common and usually easy to identify. It is not possible to distinguish benign and malignant processes without cytology or histopathology.

       Splenic hematoma and hemangiosarcoma cannot be differentiated on the basis of ultrasound alone, and may be concurrent. However, use of the Global FAST approach is helpful to rapidly screen for localized versus disseminated disease.

       If the origin of an abdominal mass is difficult to determine, move the patient from dorsal to lateral recumbency. By doing so, the liver and spleen will often separate from one another, helping to better determine the origin of the mass.

       Needle visualization by ultrasound facilitates fine needle percutaneous biopsy of the spleen. Nonspecific cytology results with fine needle biopsy do not rule out the possibility of a malignant lesion, and further diagnostics are required. However, the use of the Global FAST approach is helpful to rapidly screen for localized versus disseminated disease.

       Mild diffuse changes in echogenicity are subjective and can be challenging for the novice sonographer.

       Remember the mnemonic “SLiCK” regarding the echogenicity between the spleen (S), liver (Li), and cortex of the kidney (CK). The echogenicity of the spleen is greater (brighter) than the liver, which is slightly greater (brighter) or isoechoic (same as) than the cortex of the kidney. For the feline, hepatic echogenicity is often compared to the adjacent falciform fat and the feline liver should be isoechoic to slightly hypoechoic to the falciform fat.

       Several benign processes cause mild to moderate diffuse changes in echogenicity including extramedullary hematopoiesis, passive congestion, and antigenic stimulation.

       Diffuse changes associated with lymphosarcoma or other myeloproliferative disorders can be variable in appearance and occasionally can be associated with a normal or unremarkable splenic appearance.

       Fine needle percutaneous biopsies are indicated in cases of moderate to severe splenomegaly or in animals with diffuse changes in echogenicity.

       Spleen size is subjective. A spleen that extends to a small or medium‐sized urinary bladder is considered enlarged.

       A folded spleen in a cat is always as a general rule considered abnormal and indicates splenomegaly (Hecht 2008).

       Normal cat spleen thickness is <10 mm (Reese et al. 2013).

       Benign nodular hyperplasia usually consists of nodules that are of homogeneous echotexture being either hypoechoic or hyperechoic.

       Single target lesions have a high predictive value for malignancy. When multiple target lesions are seen, the positive predictive value of malignancy increases from 74% to 81% (Cuccovillo and Lamb 2002).

       Normal echogenicity rule of thumb: the spleen (S) is more echogenic (hyperechoic) than the liver (Li) which is the same or slightly more echogenic (brighter) than the cortex of the kidney (CK), remembered as S > Li ≥ CK or by the mnemonic “SLiCK.” For the feline, hepatic echogenicity is often compared to the adjacent falciform fat and the feline liver should be isoechoic to slightly hypoechoic to the falciform fat.

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      2 Cuccovillo A, Lamb CR. 2002. Cellular features of sonographic target lesions of the liver and spleen in 21 dogs and a cat. Vet Radiol Ultrasound 43(3):275–278.

      3 Fife WD, Samii VF, Drost JS, et al. 2004. Comparison between malignant and nonmalignant splenic masses in dogs using contrast enhanced computed tomography. Vet Radiol Ultrasound 45:289–297.

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      5 Hecht S. 2008. Spleen. In: Atlas of Small Animal Ultrasonography, edited by Penninck D, d’Anjou M. Ames: Blackwell Publishing, pp 263–280.

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      10 Nyland TG, Mattoon JS, Herrgesell EJ, Wisner ER. 2002. Spleen. In: Small Animal Diagnostic Ultrasound, 2nd edition, edited by Nyland TG, Mattoon JS. Philadelphia: WB Saunders, pp 132–133.

      11 Reese SH, Zekas LJ, Iazbik MC, et al. 2013. Effect of sevoflurane anesthesia and blood donation on the sonographic appearance of the spleen in 60 healthy cats. Vet Radiol Ultrasound 54(2):168–175.

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