Conference 02 - 2010 Case: 02 20100818

Signalment:

An 8-year-old, male, neutered, domestic-mixed breed cat (Felis silvestris).The animal presented with anorexia and in poor general condition. Blood biochemical examination revealed increased enzyme activities of aspartate aminotransferase (AST) and alkaline phosphatase (ALP). One month later, exploratory laparotomy was performed because of further worsening of body condition. The surface of the liver was irregular, and multiple small nodules were observed on the small intestine. Wedge biopsy of the liver and small intestine was performed.

Gross Description:

The surface of the biopsied liver tissue was irregular and multiple small nodules were scattered in the small intestine.

Histopathologic Description:

Liver: Neoplastic lymphocytes were observed in the cytoplasm of hepatocytes, sinusoids, interlobular veins, and the interstitium of Glisson's sheath (Fig.1). The number of neoplastic cells in the hepatocytes was one to several. Mitotic figures were often observed among the engulfed neoplastic cells. Neoplastic cells invaded the epithelial layer and lumen of the bile duct. Some hepatocytes engulfing the neoplastic cells had lipofuscin pigments or clear vacuoles in the cytoplasm. However, apparent morphological changes suggesting cell death were not detected in these hepatocytes.

A large number of neoplastic lymphocytes had round or ovoid nuclei which were elongated or cleaved in some cells. The nuclei of neoplastic cells had darkly-stained coarse chromatin and were easily distinguishable from those of hepatocytes. The neoplastic cells had a scant amount of eosinophilic cytoplasm.

In addition, varying amounts of yellow pigment were engulfed in Kupffer cells. Neutrophils and other segmented nuclear granulocytes were increased in the sinusoids and emigrated into some hepatocytes and bile ducts. Immunohistochemically, large number of neoplastic cells showed positive reaction for CD3 (Fig. 2). Positive reaction for CD20, CD56, and CD79 was not observed. Immunopositive reaction for cleaved-caspase 3 was not observed in the hepatocytes with or without infiltrated neoplastic cells. Immunohistochemical examination for proliferating cell markers, such as Ki-67 and PCNA, brought equivocal results due to the intense positive reaction of infiltrating neoplastic cells in these hepatocytes.

Morphologic Diagnosis:

Liver: T-cell chronic lymphocytic leukemia

Lab Results:

On day of first presentation: ALT 300 IU/L; ALP 130 IU/L; and Total bile acids 12.5μmol/L. One month later: ALT 600 IU/L; ALP 300 IU/L; and Total-bilirubin 2.8 mg/dL.

Condition:

Chronic lymphocytic leukemia; hepatocyte empiropolesis

Contributor Comment:

Malignant lymphoma, including the leukemic type, is the most common neoplasm of cats and accounts for more than half of all feline hemolymphatic tumors. Among the liver tumors of hematopoietic cell origin, malignant lymphoma/leukemia is also most common in the cat; however, infiltration of tumor cells into hepatocytes is rare.(2) Epithelial invasion by neoplastic cells is a characteristic feature of some special types of malignant lymphoma, such as epitheliotropic cutaneous lymphoma and primary intestinal lymphoma in dogs and cats. In addition to epithelial invasion by neoplastic cells in these types of malignant lymphomas, emperipolesis may also occur. Emperipolesis is a phenomenon in which some kind of viable cell, for example a lymphocyte, is engulfed by a large host cell without damage to either cell. This phenomenon is usually observed among cells in tissue cultures or isolated human cell smears. The phenomenon of emperipolesis has been reported to occur under various physiological and pathologic conditions. Host cells recorded to engulf lymphocytes, granulocytes, or other blood cells include mesenchymal cells, fibroblasts, thyroid epithelial cells, endothelial cells of high endothelial venule, megakaryocytes, monocytes, macrophages, and cancer cells. Normal lymphocytes, neoplastic cells obtained from leukemias, or lymphomas were also reported to be involved in emperipolesis when cultured with macrophages. The occurrence of in vivo emperipolesis in humans is very rare. In animals, reports of emperipolesis in vivo are also very rare.

The present case of feline malignant lymphoma involving the liver is considered to be the leukemic type due to the appearance of neoplastic cells in the sinusoids. Immunohistochemical findings suggest that the neoplastic lymphocytes are T-cell origin. According to the histologic criteria established by the World Health Organization (WHO), this case is T-cell chronic lymphocytic leukemia judging from the small cells with a dense chromatin distribution.

As stated above, neoplastic lymphocytes of T-cell origin occasionally have a character of infiltrating into the epidermis, the epithelium in adnexal tissues, or mucosal epithelium. In addition, as in the present case, the fact that CD3 positive neoplastic T-cell lymphocytes invaded the epithelium of a relatively large bile duct along with hepatocytes suggests that infiltration into hepatocytes reflects a common mechanism of neoplastic cells of T-cell origin.

In the present case hepatocellular damage due to intracellular invasion by neoplastic lymphocytes was considered possible; however, necrotic and apoptotic changes of hepatocytes were not detected morphologically and hepatocytes had a negative reaction for one of the enzymes concerning apoptosis, cleaved-caspase 3, by immunohistochemical examination. From these results, cytotoxic effect of infiltrating lymphocytes on hepatocytes was not evident.

JPC Diagnosis:

Liver: Malignant lymphoma, T-cell, favor mature large granular lymphocyte lymphoma with emperipolesis.

Conference Comment:

This very intriguing and diagnostically challenging case stimulated a vibrant discussion during the conference, and participants were evenly divided as to whether the lesion represented an inflammatory process or malignant lymphoid neoplasia. All participants identified an infiltrate of small lymphoid cells in the liver, with frequent occurrence of the cells in the cytoplasm of hepatocytes (emperipolesis), as described by the contributor. Close visualization of the lymphoid infiltrate under oil immersion reveals that the cells have irregularly round to ovoid, often indented nuclei with coarse chromatin and inapparent nucleoli. In some areas, eosinophilic granules are present in the cytoplasm, often within an indentation in the nucleus; phosphotungstic acid-hematoxylin (PTAH) staining of submitted serial sections performed at the AFIP better elucidated the cytoplasmic granules. Occasional mitoses are present. Based on the interpretation of morphologically abnormal lymphocytes, participants ultimately favored a neoplastic process and preferred the diagnosis of malignant lymphoma. While the infiltration of malignant lymphocytes into the liver may well represent an underlying leukemic condition, bone marrow and peripheral blood evaluation are required to document the definitive diagnosis of leukemia, and hence the diagnosis indicated above. For participants favoring an inflammatory process, an autoimmune condition was suspected as the underlying cause of the lesion.

Humans have a distinct form of hepatic lymphoma termed sinusoidal T-cell lymphoma, and its histopathologic features share similarities with the case of this cat. The primary histologic finding in the human disease is diffuse infiltration of malignant T-cells into the hepatic sinusoids in the absence of a mass effect. The histologic observation of low to moderate numbers of sinusoidal lymphocytes in the liver biopsies and the clinical presentation of affected human patients often lead to the misdiagnosis of acute or chronic inflammatory liver disease.1 The sinusoidal form of hepatic malignant lymphoma in humans demonstrates the difficulty sometimes encountered when attempting to differentiate an inflammatory process from neoplasia by histopathology.

Among the various lymphoid neoplasms affecting cats, several features in this case are suggestive for large granular lymphocytic (LGL) lymphoma, including the contributors gross report of nodular lesions in the small intestinal, cytomorphology of neoplastic cells containing eosinophilic cytoplasmic granules, and prominent emperipolesis. The most common primary site for LGL lymphoma in the cat is the small intestine; additional information concerning the gross lesions found in the small intestine, including histopathologic findings, might have been useful in this case.

This case was studied in consultation with Dr. Peter Moore, a recognized expert in the field of veterinary hematopoietic neoplasia. Dr. Moore has observed a number of similar cases in which the neoplastic lymphoid cells in feline LGL lymphoma express CD3; based on this finding and other evidence, he suspects LGL type tumors arise from intestinal epithelial lymphocytes (IEL). Dr. Moore also has observed a similar hepatic infiltration pattern for LGL lymphoma in dogs, albeit without the intestinal association; publication of the canine form of the disease is forthcoming. An IEL origin for the malignant lymphoid cells might well explain the unique histologic infiltration pattern observed in the liver of this cat, as most cases of LGL lymphoma in cats have intestinal involvement with frequent involvement of the liver, and disseminating lymphomas frequently metastasize to the liver along hepatic sinusoids.(1,3)

We thank Dr. Moore for his informative consultation with this case.

References:

1. Ishak KG, Goodman ZD, Stocker JT: Primary hepatic lymphomas and suspected lymphomas. In: Atlas of tumor pathology: Tumors of the liver and intrahepatic bile ducts 3rd series, fascicle 31, pp. 335-338. Armed Forces Institute of Pathology, Washington, DC, 2001
2. Ossent P, Stockli RM, Pospischil A: Emperipolesis of lymphoid neoplastic cells in feline hepatocytes. Vet Pathol 26:279-280, 1989
3. Valli VE: T-cell and NK-cell neoplasms. In: Veterinary Comparative Hematopathology, pp. 304-306. Blackwell Publishing, Ames, IA, 2007