“Willy” is a 5 year old M/N Golden Retriever with Grade 3 Mast Cell Tumor that was removed from the right thorax. An abdominal ultrasound with focus on the liver and spleen was requested in order to further stage his mast cell disease. CBC showed mild normocytic normochromic anemia with a hematocrit of 34%. Chemistry profile was normal. Ultrasound examination of the spleen showed the following:
Fig. 1: This is Willy’s spleen (above image). Note: Spleen is isoechoic to left renal cortex. Note parenchyma is mildly diffusely mottled. Spleen size is considered normal.
Fig. 2: This is a normal spleen (above image). Note it is hyperechoic to renal cortex.
The spleen was considered normal in size. The margins of the spleen were smooth. The splenic parenchyma was isoechoic to renal cortex (compare to left kidney in picture) and the parenchyma was mildly diffusely mottled. Normal splenic parenchyma should be hyperechoic to the renal cortex (see below). Several fine needle biopsies were obtained and submitted for cytological evaluation. Results of cytology confirmed metastatic mast cell tumor in the spleen.
The focused use of ultrasound to evaluate the spleen may answer clinically important questions and help more expediently guide further diagnostic evaluation and therapy than without using ultrasound.
Important: It should be noted that a complete abdominal ultrasound is preferred over a focused exam when one is evaluating for a mass lesion based on abdominal palpation and/or abdominal radiographic findings. A focal mass may be missed on a focused exam and it is helpful to evaluate for additional abdominal metastasis and the presence of free fluid or hemoabdomen, and therefore, a complete exam is indicated. In this blog, we will focus on evaluating diffuse parenchymal changes.
When assessing the spleen, systematic evaluation should include the following 4 features:
- Estimation of size. This is generally subjective except in cases of marked splenomegaly.
- Changes in echogenicity of the parenchyma. Evaluation of diffuse parenchymal disease is subjective and can pose difficulty for the novice sonographer. Echogenicity of the spleen is assessed by comparing splenic parenchyma to the adjacent liver and the left renal (kidney) cortex as described above. Changes in echogenicity can be seen with extramedullary hematopoiesis, passive congestion, nodular hyperplasia, inflammation, infection, neoplasia and splenic torsion.
- Presence of mass lesions and nodules.
- Assessment of splenic vasculature.
- It is important to remember that normal ultrasound appearance of spleen does not rule out infiltrative disease especially lymphosarcoma or mast cell tumor. If these diseases are suspected, then fine needle biopsies should be performed for additional evaluation.
Common conditions of the spleen:
Extramedullary Hematopoiesis. Generally associated with mildly reduced echogenicity (hypoechoic).
Passive Splenic Congestion. Generally associated with hypoechoic changes in acute phases but may be associated with hyperechoic changes in more chronic processes. Generally, architecture is not disrupted.
Nodular Hyperplasia. May be associated with either hypoechoic or hyperechoic changes which are relatively mild. The splenic capsule may be mildly irregular as described above. Nodular hyperplasia is a benign condition commonly seen in older dogs.
Inflammatory or Infectious Diseases (fungal, bacterial, Rickettsial). Generally these conditions cause mild to moderate splenomegaly with diffuse hypoechogenicity. With acute inflammation or infection, the changes are more pronounced with a more prominently hypoechoic and finely mottled appearance.
Neoplastic Conditions. Lymphosarcoma, mast cell tumor and other myeloproliferative diseases may produce a diffusely coarsely mottled appearance referred to as a honeycomb, moth-eaten or Swiss cheese appearance. It is important to remember that both lymphosarcoma and mast cell tumor can also be present with very mild diffuse changes and occasionally can even have a fairly normal appearance. In addition, parenchyma may be hyperechoic rather than hypoechoic.
Determining the significance of subtle changes in echogenicity can be challenging as seen in the examples below.
This is a normal spleen.
This spleen has infiltrative mast cell tumor.
The take home message is this: you cannot definitively determine whether or not an infiltrative disease is present without taking samples for cytological or histological evaluation.