Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Группа авторов

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.

      Neoplasia

      Splenic neoplastic lesions can have a wide range of ultrasonographic changes. As emphasized above, it is not possible to distinguish between benign and malignant lesions based on ultrasonographic appearance alone. The most common types of splenic neoplasia found in dogs are hemangiosarcoma and lymphosarcoma (Hecht 2008) but other primary and metastatic tumors are possible.

       Hemangiosarcoma (HSA) generally appears as complex mass lesions with mixed echogenicity and cavitations that distort the splenic capsule (Figure 9.12). HSA of the spleen is often associated with acute or chronic hemorrhage, and animals with ruptured splenic masses causing hemoabdomen have a higher likelihood of malignancy (hemangiosarcoma) (Hammond and Pesillo‐Crosby 2008). Definitive preoperative diagnosis of HSA is challenging, however, since rupture of splenic masses with resultant hemoabdomen can occur with both benign and malignant processes, and since benign hematomas and HSA can have similar ultrasonographic appearances. The presence of suspected metastatic nodules elsewhere in the abdomen or thorax increases the index of suspicion for malignancy, but a definitive diagnosis is often not made without splenectomy and histopathology, and even then can be complicated by an associated hematoma.

Figure 9.9. Splenomegaly with splenic hypoechogenicity (darker than normal). (A) Comparative echogenicity of the spleen to the cortex of the left kidney. Suppurative splenitis was diagnosed by percutaneous needle biopsy. (B) Splenomegaly determined by a splenic thickness that was >10 mm (measured by calipers marked “A”) with concurrent hypoechogenicity (darker) in a cat. Histoplasmosis was diagnosed by percutaneous needle biopsy. (C) Diffuse parenchymal changes not much different from (A) and (B) diagnosed by percutaneous needle biopsy as mast cell tumor. These examples illustrate that clinical diagnosis cannot be made based on ultrasonographic appearance alone.

      Pearl: Staging of HSA may be assisted by performing a Global FAST to evaluate for hemoabdomen (AFAST), pericardial effusion (and right atrial mass) and Vet BLUE lung ultrasound for pulmonary metastasis.

       Metastatic lesions may be hypoechoic or hyperechoic in nature and are more likely to have a “target” appearance consisting of hypoechoic margins with a relatively hyperechoic center (Figure 9.13). Single target lesions have a high predictive value for malignancy and when multiple target lesions are seen, the positive predictive value of malignancy increases from 74% to 81% (Cuccovillo and Lamb 2002). One must keep in mind, though, that a sonographic target lesion is a nonspecific finding and a biopsy is required for diagnosis. When finding a splenic target lesion, look for other intraabdominal or intrathoracic masses using Global FAST, radiography (screening for lung nodules) or both. The identification of additional nodules provides further suspicion for malignancy and may also provide a more accessible scanning plane for percutaneous sampling.Figure 9.10. Splenic nodular hyperplasia and myelolipomas. (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