Breed: Beagle Mix
Gender: Female, Spayed
A six year old female spayed Beagle mix presented to a referral neurology service with acute onset seizures. The neurologist detected a brain mass via MRI. The owner elected to pursue surgery to determine the identity of the lesion and if it could be resectable. An impression smear and a biopsy of the mass were submitted to our lab. The impression smear was stained with a Wrights stain and examined.
500x magnificationClick here for the IDEXX Pathology Report for the slides above.
Microscopic description: The slides reveal a high cellularity consisting of a markedly atypical cell population. They are comprised predominantly of large atypical oval shaped cells observed mostly in aggregates and sometimes individually. These cells reveal large round to oval nuclei with finely to coarsely stippled nuclear chromatin and a large amount of often highly vacuolated light basophilic cytoplasm. Nucleoli are usually evident with many marco-nucleoli noted. The cells exhibit marked anisocytosis and anisokaryosis, high nuclear to cytoplasmic ratios, and binucleation and multinucleation. Mitotic figures are seen. Low to moderate numbers of lymphocytes, nondegenerate neutrophils and occasional plasma cells are seen but the distribution of these cells varies between areas of the slides.
Interpretation: Malignant neoplasia; consistent with Histiocytic sarcoma
The Biopsy sample was formalin fixed, stained with H&E stain and examined histopathologically.
400x magnificationClick here for the IDEXX Pathology Report for slides 3 and 4, and for the case.
Microscopic Description: The sections are composed of a densely cellular neoplasm comprised of cells arranged in closely packed sheets and occasional haphazardly arranged streams supported by a fine fibrovascular stroma. Tumor cells are large and round to oval with a moderate to large amount of eosinophilic, homogenous to vacuolated cytoplasm with distinct cellular borders. Nuclei are eccentric, round to reniform or oval with stippled or vesicular chromatin and have 1-3, prominent, deeply eosinophilic nucleoli. There is moderate anisocytosis and marked anisokaryosis with frequent karyomegalic and large multinucleated cells distributed throughout the mass. The mitotic index is greater than 30 per 10 high power fields. (400x); some mitoses are atypical in appearance. There are mild to moderate and diffuse infiltrates of lymphocytes, plasma cells and lesser numbers of neutrophils.
Histologic Interpretation: Histiocytic sarcoma. Mitotic index: Greater than 30 per 10 high power fields. Angiolymphatic invasion is not observed. Surgical margins: Neoplastic cells extend to the edges of the biopsied tissue.
This lesion was consistent with a primary histiocytic sarcoma of the brain. This tumor type, in this location is very uncommon but has been described previously. Although brain lesions can rarely manifest in patients with disseminated histiocytic sarcoma, solitary histiocytic sarcoma of the brain is more common. These tumors are usually located in the cerebrum and usually involve the frontal lobes.
As was the case in this patient, seizures are a typical presenting finding, this tumor most commonly occurs in middle aged to older patients. Pure breed dogs are most commonly affected with Bernese Mountain dogs, Retrievers and Rottweilers being the most common breeds but other breeds including Corgis, Beagles and Shetland sheep dogs have also described. The cell of origin of this tumor within the brain is suspected to be resident dendritic cells or macrophages of the meninges or choroid plexus, but most seem to be of dendritic origin.
Histologically, these tumors are poorly demarcated with invasion of the brain parenchyma and these patients currently have a grave prognosis. Immunohistochemical or special stains may be helpful with further identification of this tumor, especially if the morphology is not as typical of a histiocytic sarcoma (which was not the case in this patient). Stains including MHCII, CD18, CD204 and lysozyme have been helpful for further confirmation of this tumor type.
This patient was euthanized shortly after surgery due to declining condition and grave prognosis.
- Thongtharb et.al. ‘Histologic and immunohistochemical studies on primary intracranial canine histiocytic sarcoma’J Vet Med Sci, 2016 Apr 78(4) 593-599
- Ide et.al. Pathological and immunochemical features of subdural histiocytic sarcomas in 15 dogs’. J Vet Diagn Invest, 2011 Jan 23(1): 127-32.