Canine Splenic Pathology: a Retrospective Study of 109 Surgical Samples, with Special Emphasis on Fibrohistiocytic Nodules

In order to assess the relevance of canine splenic pathology, to emphasise the differential diagnostic criteria among splenic haematoma, haemangioma and haemangiosarcoma, and to focus on the recently proposed classification of canine splenic fibrohistiocytic nodules (FHN), a retrospective study was carried out on HE-stained sections from formalin-fixed and paraffin-embedded samples from 109 spleens after splenectomy. FHN were also stained by Masson trichrome, Gomori for reticulin, Perls for hemosiderin, toluidine blue and immunohistochemistry (CD3, BLA.36, MAC.387, lysozyme, F-VIII-RA, S100, vimentin, desmin, sm-actin and MIB-1). Spleens were resected because of diffuse splenomegaly (49%) or nodular distortion (51%). Microscopic changes consisted of myeloid metaplasia and erythrophagocytosis in 25 cases (23%), hyperemia (13%), haematoma (9%), haemangioma (4%), haemangiosarcoma (11%), nodules of combined lymphoid and fibrohistiocytic cell proliferation (16%), secondary lymphoma (7%), metastasis of carcinoma (4%), splenitis (5%) and others lesions (10%). Splenectomy is a “common procedure” in the dog, but it is usually performed without a definitive clinical diagnosis and prognosis, which necessitate subsequent histopathologic examination. The differential diagnosis between splenic haematoma and haemangiosarcoma can be very difficult if the surgical specimen is not correctly sampled. The histological pattern of FHN ranged from nodules of lymphoid hyperplasia including a distinct population of spindle and/or histiocytic cells sometimes displacing the follicular architecture of the nodule, up to true fibrohistiocytic neoplasms. Morphology and immunohistochemistry seem to prove that FHN are a continuum from benign nodular hyperplasia to malignant fibrous histiocytoma.