Uterine B cell lymphoma in a mare



In this report, we describe the diagnostic findings and outcome of a uterine B cell lymphoma in a mare. A well circumscribed uterine mass with significant peripheral vascularisation was identified by transrectal ultrasonography during the reproductive examination of an 8-year-old Thoroughbred mare. Subsequent hysteroscopy revealed that the uterine mass was located intramurally and contained a protruding polyp-like structure. A diagnosis of uterine B cell lymphoma was established by histopathological examination of a hysteroscopically-obtained tissue sample. Additional diagnostics demonstrated that the uterus was a site of metastasis. Due to her deteriorating condition, extensiveness of the tumour and poor prognosis, the owner decided that the mare should be subjected to euthanasia.


A pathological uterine mass in the mare may be a differential cause of infertility and can generally be detected during examination of the reproductive organs by either transrectal palpation, ultrasound or hysteroscopy. Differential diagnosis of a uterine mass includes uterine neoplasia (McCue 1998), haematoma (Pycock 1994), abscess (Van Camp 1993) and endometrial cysts (Stanton et al. 2004). Uterine neoplasia is considered to be a rare condition in the mare. The most frequently reported equine uterine tumour is a leiomyoma, a benign neoplasm of smooth muscle origin (McCue 1998). Several other uterine tumours including fibroleiomyoma (Romagnoli et al. 1987; Broome et al. 1992), leiomyosarcoma (Lofstedt et al. 1987), rhabdomyosarcoma (Torbeck et al. 1980), lymphosarcoma (Neufeld 1973), adenocarcinoma (Gunson et al. 1980) and T cell lymphoma (Freeman et al. 1997) have been previously described in the mare. The terms lymphoma and lymphosarcoma are commonly used synonymously to describe a malignant tumour of the lymphoid tissue. Equine lymphomas have been classified into 4 forms. The multicentric form, which involves lymph nodes and multiple organ systems, is the most common type (Meyer et al. 2006). Other forms include alimentary (Taylor et al. 2006; Mitsui et al. 2007), mediastinal (Garber et al. 1994; De Clercq et al. 2004) and the cutaneous form (Gerard et al. 1998; Henson et al. 1998; Epstein and Hodge 2005). Further classification of lymphomas as either B or T cell is based upon the cell type of origin and the expression of certain antigens by the neoplastic lymphocytes. The majority of equine lymphomas are T cell in origin (Meyer et al. 2006). This case report describes the clinical presentation, diagnosis and pathological features of a B cell equine lymphoma involving the uterus.

Case details


An 8-year-old Thoroughbred mare presented to the Veterinary Medical Teaching Hospital (VMTH), University of California, Davis, for a reproductive examination. Early in the previous breeding season, the mare had given birth without assistance to her first foal. Reproductive examination of the mare by transrectal ultrasonography 30 days post partum by the referring veterinarian revealed a mass within the left uterine horn and a presumptive diagnosis of uterine haematoma was made. Subsequent attempts at breeding over 3 cycles during the same season were unsuccessful and following these attempts hysteroscopy was performed. Endometrial cysts along the base of the mass were laser ablated.

Clinical findings

The mare presented in moderate body condition and no significant abnormalities were detected on physical examination. A small amount of sanguineous discharge was noticed on the ventral commissure of the vulva. Palpation per rectum of the internal reproductive tract was performed and a firm mass located near the tip of the left uterine horn was detected. Transrectal ultrasound examination with a linear-array transducer of 7.5 MHz (Medison Pico)1 revealed a well circumscribed 5 x 5 cm hyperechoic mass within the wall of the left horn. Colour Doppler ultrasonography showed significant vascularisation (Fig. 1) at the periphery of the uterine mass. Endometrial samples were collected using a double guarded cotton swab and cytology brush2 and submitted for cytological examination as well as aerobic and nonaerobic bacteriological culture. No inflammatory cells were detected on the endometrial cytology and culture revealed no bacterial growth. Visual examination of the vagina and cervix with a glass speculum revealed no significant abnormalities. Subsequent hysteroscopy using a flexible Olympus endoscope3 revealed a grey, oblong, cyst-like structure surrounded by a small amount of dark sanguineous fluid at the base of the left horn. A polypectomy snare4 with a loop was introduced through the biopsy channel of the endoscope and was tightened around the cyst-like structure. The structure was friable and a small section was retrieved and submitted for histopathology. The endoscope was advanced further up the left horn and an irregular shaped intramural mass with a protruding polyp-like structure (Fig. 2) was visualised. This polyp-like structure was snared, removed and also submitted for histopathology. Following these procedures the uterus was lavaged with 5 l lactated Ringer's injection USP5 solution. Based on the performed diagnostics, a presumptive diagnosis of uterine neoplasia was made. After consultation with the owner, the mare was discharged from the VMTH while awaiting histopathology results.

Figure 1.

Ultrasound image of the uterine mass (A) near the tip of the left uterine horn. Significant vascularisation at the periphery of the uterine mass is demonstrated by the white arrow.

Figure 2.

Hysteroscopic view of the irregular shaped uterine mass (A) at the tip of the left horn with a protruding polyp-like structure (B).


The cyst-like structure detected at the base of the left horn was comprised of viable and necrotic fibroblasts and degenerate collagen fibrils overlying abundant necrotic cellular debris. Due to extensive necrosis, it was not possible to determine the exact origin of this tissue; however, the authors speculate that this tissue was either a remnant from the cyst ablation performed by the referring veterinarian or neoplastic tissue exhibiting extensive necrosis.

The submucosa of the second submitted sample was infiltrated by densely cellular sheets of atypical round cells (Fig. 3) within a highly vascular and congested connective tissue stroma. The atypical round cells were angular to round, had high nuclear:cytoplasmic ratios and contained amphophilic to lightly basophilic cytoplasm with occasional lightly eosinophilic perinuclear regions. These cells had one to rarely two paracentrally located nuclei and contained densely clumped chromatin. There was moderate anisocytosis with cells varying from approximately 10–25 microns in diameter. Mitoses varied from 0–6 per high power (400x) field. Sheets of the atypical round cells multifocally obliterated vessel walls and infiltrated into vascular lumina. Moderate numbers of pyknotic neoplastic cells and degenerate neutrophils were scattered throughout the examined sections. The mass was characterised by immunohistochemical staining. The neoplastic cells were strongly positive for CD79a (B cell marker) and negative for CD3 (T cell marker). Few scattered to moderate numbers of clustered small round cells stained positively for CD3. These were interpreted to be a mature T cell infiltrate within the neoplastic B cell population.

Figure 3.

Histological section (H&E stain, Bar=50 µm) of the uterine lymphoma showing neoplastic B cells infiltrating the uterine submucosa. Eosinophilic perinuclear regions (black arrowhead), binucleated cells (arrow A) and bizarre mitoses (arrow B) are present among the neoplastic B cell population. Inset (top left): Neoplastic B cells exhibit strong CD79a (B cell marker) immunoreactivity (Bar=100 µm).


Histopathological findings were consistent with a uterine B cell lymphoma.

Other diagnostics

Further investigation to determine the primary site ofthe neoplasm was recommended to, but declined by, the owner. After one month, the mare re-presented to the VMTH following marked weight loss over the prior week. On admission, the mare was depressed and in poor body condition (BCS = 2/9). Clinical examination revealed a temperature of 37.3°C, heart rate of 48 beats/min, respiratory rate 24 breaths/min and no evidence of peripheral lymphadenopathy. No other significant abnormalities were detected. Results of a complete blood count and serum biochemical analysis revealed a neutrophilia (16.2 × 109 cells/l, reference range [rr]: 2.6–6.8 × 109 cells/l) with a regenerative left shift, elevated total protein (86 g/l, rr: 58–77 g/l) and globulin (56 g/l, rr: 16–50 g/l).

A complete transabdominal ultrasound examination was performed using a 4.0 MHz curvilinear transducer with a Biosound Technos6 ultrasound machine. Ultrasound examination revealed a very large, irregularly-shaped, heterogeneous mass measuring approximately 77 cm × 72 cm × 26 cm that appeared to arise from the spleen. The spleen was recognisable but was nearly obliterated by the mass. Multiple smaller, homogeneous hypoechoic masses measuring up to 13.5 cm × 7.1 cm were seen throughout the abdomen adjacent to the left kidney, stomach and within the mesentery. The right and left liver lobes were unremarkable with the exception of mildly dilated vasculature. Moderate sized pockets of cellular peritoneal effusion were seen throughout the ventral abdomen.

Abdominocentesis was performed to obtain peritoneal fluid. Peritoneal fluid analysis yielded red, opaque fluid with a nucleated cell count of 21.3 × 109 cells/l (rr: 0.05–4.6 × 109 cells/l), total protein concentration of 52 g/l (rr: 2–15 g/l) and total red blood cell count of 0.78 × 1012 cells/l (rr: 0–0.0425 × 1012 cells/l). Cytological evaluation of the peritoneal fluid revealed predominately (85%) nondegenerated neutrophils (rr: 0–56%). Due to metastasis of the lymphoma and poor prognosis for life, the owner elected to subject the mare to euthanasia.

Post mortem findings

On post mortem examination, there was a large (Fig. 4), poorly delineated, yellow-light tan, multilobulated mass (length: 86 cm, width: 67 cm, circumference: 146 cm, weight: 57 kg) that incorporated the spleen, left kidney and left adrenal gland. On the parietal surface of the peritoneal abdominal wall, there were several small masses similar in appearance to the splenic mass. The sternal, hilar, mesenteric and pelvic lymph nodes were enlarged. A moderately circumscribed, yellow-white nodular mass (Fig. 5) was present within the wall of the left uterine horn. Histological examination of the splenic mass, uterine mass and sternal, hilar, mesenteric and pelvic lymph nodes confirmed the presence of lymphoma of B cell origin.

Figure 4.

Necropsy view of the large multilobulated abdominal mass (A) and a small mass (arrow) incorporated in the peritoneal abdominal wall.

Figure 5.

The uterus is dissected through the ventral aspect. Macroscopic view of the irregularly-shaped uterine lymphoma (A) at the tip of the left horn.


Uterine lymphoma is an extremely rare phenomenon in the horse. To the authors' knowledge, uterine B cell lymphoma in the mare has not previously been reported in the literature. A few other reports showed involvement of the uterus although these reported cases were either T cell lymphoma (Freeman et al. 1997) or were cases in which the cell lineage was not well defined or reported (Neufeld 1973; Sweeney et al. 1991). In all the described reports of equine uterine lymphoma, including this report, the uterus was a site of metastasis (multicentric form). Although extremely rare, primary uterine lymphomas are described in women and are predominantly of B cell origin (Noelle et al. 2006).

A history of infertility (Quinn and Woodford 2005) and presence of sanguineous vaginal discharge (Brandstetter et al. 2005; Frazer 2005), as described in this report, were also reported as possible sequelae of a uterine leiomyoma. A variety of factors could have attributed to the mare's history of infertility. The presence of a negative culture and cytology does not completely exclude the diagnosis of endometritis since these diagnostic tests do not have 100% sensitivity (LeBlanc 2010). Other possible explanations include the persistent presence of uterine fluid combined with impaired uterine clearance, reduced trans-uterine embryo migration or embryo fixation (Berezowski 2002). Ultrasonography is a useful tool in the diagnosis of a uterine tumour; however, it is not possible to differentiate the different types of uterine tumours. Biopsy of the uterine mass was necessary to obtain a definitive diagnosis.

The clinical presentation of equine lymphoma is not pathognomonic. Weight loss, as described in this report, is a common finding followed by ventral oedema. A variety of haematological abnormalities such as hyperfibrinogenaemia, hypoalbuminaemia, anaemia, leukaemia, hyperglobulinaemia and thrombocytopenia have been described as common findings in equine lymphomas (Meyer et al. 2006).

In a case of primary uterine lymphoma located in one of the horns, unilateral ovariectomy and partial hysterectomy would be an appropriate therapy which still could result in the ability to conceive and carry a foal to term (Santschi and Slone 1994). Since most equine lymphomas are multicentric, chemotherapy is the only available treatment. A few protocols to treat equine lymphomas have been described (Saulez et al. 2004). Due to the extent of this lymphoma and involvement of multiple organ systems, none of the previously described treatments would result in a positive outcome and euthanasia was the only reasonable option.

Although the most common equine uterine tumour, the leiomyoma, is benign and causes few to no systemic clinical signs, this report emphasises that benign uterine tumours must be distinguished from malignant tumours so that other diagnostic tests may be performed to determine the primary site of the neoplasm as well as evaluate the extent of metastasis.

Authors' declaration of interests

No conflicts of interest have been declared.

Manufacturers' addresses

1 Medison Pico, Universal Ultrasound Systems Inc, Bedford, New York, USA.

2 Minitube of America, Inc, Verona, Wisconsin, USA.

3 Olympus CV-100 Video System, Olympus America Inc, Center Valley, Pennsylvania, USA.

4 Endoscopy Support Services Inc, Brewster, New York, USA.

5 Baxter Healthcare Corporation, Deerfield, Illinois, USA.

6 Biosound Technos, Universal Ultrasound Systems Inc, Bedford, New York, USA.