Organ of the month: Spleen

I. Indications for splenic biopsy

Due to the nature of the spleen, a biopsy with the intention of histopathology is always going to be excisional. Incisional core biopsies are possible but not routine.  Fine needle aspirates may of course form part of an initial investigation into splenic disease or cancer staging. However, reliable and meaningful histopathology requires splenectomy. Indications for splenectomy include a splenic mass or neoplasia; splenomegaly; traumatic injury; and splenic torsion1.

II. Different types of biopsy

Punch, wedge and even Tru-cut biopsies need not apply!  Please read on for advice on how to sample spleens and splenic lesions.

III. How to sample and send splenic samples

The gold standard way to sample the spleen following splenectomy is NOT to sample.  Submitting the entire spleen is more likely to lead to a definitive diagnosis than even multiple sections2. Our fact sheets on splenic sampling and submission of whole organs provide more details3,4.  It is best to fix the entire spleen at your practice in a large bucket that allows the entire spleen to be submerged in 10% neutral buffered formalin (NBF). After about 3-4 days, the spleen can be sent in a smaller volume of formalin, wrapped in gauze or paper towels pre-soaked in 10% NBF, then double bagged and, ideally, placed in a protective container.  Prior to fixation, a series of partial incisions made through the capsule will allow better formalin penetration.  Please bear in mind that spleen is an organ that often takes longer to fix and it may still require a more prolonged fixation time, even after arriving at the laboratory. This is mainly due to its high blood content. 

If sending the entire organ is not feasible, then submission of selected, representative sections is the next best option, ideally supported by annotated photographs. When sampling nodules, we strongly advise sampling of the transition area between the nodule and the surrounding spleen.  Sampling the centre is likely to capture only blood and may miss more diagnostic peripheral tissue, particularly in haemangiosarcoma (see Fig 1).

Fig 1. Sampling of splenic nodules (X marks the spot to avoid)

IV. Relevant clinical information

  1. Signalment: Since neoplasia is more likely in older animals, with the exception of lymphoma, the age of the animal is helpful. Certain breeds of dog are more prone to some forms of neoplasia, so this also important information.
  2. Brief summary of clinical signs and reason for splenectomy.
  3. Results of other tests, especially haematology, but also any relevant biochemical abnormalities.
  4. Particularly if you are unable to send the entire spleen, a summary of its gross appearance is important. General enlargement (splenomegaly); nodular (if so, number, size, colour and consistency of nodules; a range is fine if there are many nodules). Consider sending images.

V. Diagnoses in splenic submissions

In dogs, pathological findings vary a little with different studies but, as a broad rule of thumb, approximately half of splenic lesions are neoplastic and half non-neoplastic. Approximately 50% of neoplastic lesions are haemangiosarcoma2,5.  Other potentially malignant neoplasms are less common but include lymphoma, histiocytic sarcoma and metastatic neoplasia. Nodular hyperplasia or haematoma formation are the most common benign lesions and both are obviously non-neoplastic. Benign splenic neoplasms are very uncommon but include haemangioma (actually quite rare), lipoma and myelipoma. Other non-neoplastic lesions include infarcts, abscesses, torsion and extramedullary haematopoiesis.

Diagnosis of splenic disease in cats is much less common. Feline splenic lesions include nodular hyperplasia, haematoma, splenitis and neoplasia, both primary and metastatic. One recent study of 62 cats found that neoplasia was the most common diagnosis (81%) and, of those, the most common diagnoses were mast cell tumour, haemangiosarcoma, lymphoma and histiocytic sarcoma6.

VI. Histopathology of splenic lesions

Fig 2. Splenic haemangiosarcoma outlined in yellow. The rest of the section consists only of blood, illustrating how localised the tumour can be and how easy it is to miss if only sending sections.
Figs 3 and 4. Splenic haemangiosarcoma (arrow = mitotic figure)
Fig 5. Splenic nodular hyperplasia
Fig 6. Inset from Fig 5

Useful References

  1. Murgia D (2016) Splenectomy cases in dogs. Veterinary Times Nov 1:pp1-8.
  2. Day, MJ, Lucke, VM and Pearson, H (1995). A review of pathological diagnoses made from 87 canine splenic biopsies. Journal of Small Animal Practice, 36, 426-433.
  3. Splenic sampling fact sheet. https://www.finnpathologists.com/wp-content/uploads/2023/11/FINN-Fact-Sheet-3-Splenic-Sampling-Issue-3-04.07.2023-1.pdf
  4. Submission of whole organs. https://www.finnpathologists.com/wp-content/uploads/2023/11/FINN-Fact-Sheet-9-Submission-of-Challenging-Samples-Issue-2-04.07.2023-1.pdf
  5. Lee M, Park J, Choi H, Lee H and Jeong SM (2018) Presurgical assessment of splenic tumors in dogs: a retrospective study of 57 cases (2012-2017). J Vet Sci 19:827-834.
  6. Rossanese M, Williams H, de la Puerta B, Scott P, Chanoit G and Guillén A (2023) Prevalence of malignancy and factors affecting outcome of cats undergoing splenectomy. JAVMA 261:1646-1652.

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