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).
Vasculature
Finally, evaluation of the splenic vasculature may help identify splenic torsion (Figure 9.16) (see above), thrombus formation, and splenic infarction.
Thrombi are visualized as echogenic structures within the splenic vein or parenchymal splenic vessels, and may or may not have clinical consequences depending on the degree of occlusion of the vessel (Figure 9.17; compare to Figure 9.1). Their presence, however, does raise clinical suspicion for lymphosarcoma (Laurenson et al. 2010). See also Chapter 25.
Pearl: Splenic thrombi are most commonly associated with lymphosarcoma (Laurenson et al. 2010). They can also be seen with splenic torsion.
Splenic infarction is a possible sequela to splenic thrombi and occurs when blood flow is occluded to an area of splenic parenchyma due to torsion or trauma. Infarcted areas tend to be hypoechoic due to edema in the acute phase, while having borders that are variable in appearance ranging from poorly defined to sharply delineated margins. The lesions generally become smaller and hyperechoic with time (see Figures 9.11 and 16.10B).
Figure 9.17. Splenic thrombus. (A) The splenic vein near the hilus appearing distended by its relative size to the body of the spleen. Within the lumen there appear to be isoechoic material/intraluminal echoes. (B) Same image as (A) confirming the presence of the suspected splenic thrombus using color flow Doppler. Splenic thrombi are most commonly associated with lymphosarcoma but are also associated with other prothrombotic conditions.
Routine Add‐on of AFAST and Its Abdominal Fluid Scoring System (or Global FAST)
In the authors' experience, it is extremely valuable to perform an AFAST examination with assignment of an abdominal fluid score in either lateral recumbency for the best approach. The positioning of small animals in dorsal recumbency for POCUS abdominal organ examinations can obscure small‐volume peritoneal effusion and underestimate the volume of effusion present because peritoneal effusion will flow into the less sonographically accessible diaphragmatic recesses. AFAST improves the diagnostic potential of ultrasound by detecting peritoneal effusion. The early detection of abdominal effusion is clinically important and helps direct additional diagnostic recommendations while avoiding morbidity, complications, and patient mortality in the event the effusion is missed.
The Global FAST approach is used as a screening test to rapidly discriminate between localized and disseminated disease, comorbidities, and complications. Global FAST offers a rapid assessment of the abdomen (AFAST) and to survey for pleural and pericardial effusion (TFAST),and cardiac and pulmonary abnormalities (TFAST and Vet BLUE), including lung nodules, with minimal restraint upon initial patient triage.
Pearls and Pitfalls, The Final Say
It is important for the nonradiologist veterinarian to respect the limitations of the POCUS spleen examination because of the sonographic variability of many diffuse and nodular conditions. Fortunately, the spleen is amenable to minimally invasive cytological evaluation by percutaneous needle biopsy or aspirates when sonographic abnormalities are identified.
Although hemorrhage is an uncommon complication of percutaneous fine needle biopsy, the AFAST format with fluid scoring system (see Chapters 6 and 7) is an excellent tool for postsampling monitoring (four hours post procedure and as needed thereafter), and is more sensitive than traditional means such as packed cell volume (hematocrit) for occult hemorrhage. Finally, a splenectomy with appropriate culture and histopathological testing may be required for definitive diagnosis and treatment plan, and the spleen may be surgically removed with little long‐term consequence in both dogs and cats. Global FAST is an especially helpful approach to rapidly survey for pleural and pericardial effusion, and cardiac and pulmonary abnormalities, and is used as a screening test to rapidly discriminate between localized and disseminated disease, comorbidities, and complications (see Chapters XX and XX).
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
