Splenic nodules or masses are extremely common findings when ultrasounding the canine abdomen. Nodules are small, circular abnormalities within the spleen that might be hyperechoic (brighter) or hypoechoic (darker) than the surrounding, normal spleen. Nodules are small (less than 4 cm diameter) and masses are larger (greater than 4 cm diameter), but these are descriptive terms. The nodule or mass can also have mixed echogenicity, or both hypoechoic and hyperechoic regions.
There are many benign causes of splenic nodules and masses. These include nodular hyperplasia (extra splenic tissue), extramedullary hematopoesis (blood cell production outside of the bone marrow), granuloma (older inflammatory tissue), hematoma (blood leakage into the spleen), and myelolipoma (fat deposits). Myelolipomas are a bit more characteristic, as they are hyperechoic and surround the splenic veins near the medial surface.
Unfortunately, more serious diseases such as cancer and infarction, though less common, have similar characteristics. With ultrasound examinations, we can not always tell whether a nodule or mass is benign or malignant. If the lesion is large, and distorting the margin of the spleen by bulging outward, we are more likely to think it is a malignant disease. Regarless of the lesion size, the only way get a diagnosis is to perform a fine needle aspirate of the nodule or mass.
Splenic lesions in cats are taken more seriously, as about half of them are benign and half are malignant. Splenic enlargment or any type of focal splenic lesion should be follwed up by a fine needle aspirate in cats.
While aspirates give us the diagnosis in the majority of cases, they are not always successful. The type of lesion we are dealing with determines whether any cells will be available for sampling. In a small lesion, the chances are good that we will get a representative sample. In a large lesion with lots of bleeding, like a hemangiosarcome (cancer) or a hematoma (just blood), the majority of the mass is made of red blood cells, and it can be impossible for the pathologist to tell them apart. The size and imaging characteristis of the mass, as well as the animal’s other test results will help the clinician decide if a recheck of the lesion to monitor growth, an aspirate, or surgery to remove the spleen is the best option.
Ultrasound is very good at detecting splenic lesions, but not specific for determining whether they are benign or malignant. Repeat ultrasound examinations, fine needle aspirates and splenectomy are all options to help determine what the best option is for diagnosis and treatment.