What ails the pet rat? A retrospective study of more than 300 biopsy samples of externally palpable masses submitted from pet rats for histopathology (2013-2021).

Biopsy data on externally palpable masses in pet rats (Rattus norvegicus) were retrieved from the archives of a large commercial pathology laboratory between November 2013 and July 2021. A total of 330 samples were submitted from 292 individual animals. Of the 330 samples submitted, 182 (55.2%) were of mammary gland origin and the majority were benign neoplasms, with fibroadenoma most frequent. Of the remaining 148 samples, 101 were neoplastic in nature, with 76 tumours classified as mesenchymal, 23 as epithelial and two classified only as malignant neoplasia not otherwise specified. Malignant neoplasms accounted for 88 of these non-mammary masses, with the most diagnosed tumours including soft tissue sarcoma (including fibrosarcoma) and sarcomas not otherwise specified.

Lumpy, bumpy guinea pigs: a retrospective study of 619 biopsy samples of externally palpable masses submitted from pet guinea pigs for histopathology.

Biopsy data on externally palpable masses in pet guinea pigs were retrieved from the archives of a large commercial pathology laboratory between November 2013 and July 2021. Of the 619 samples submitted from 493 animals, 54 (8.7%) had arisen from the mammary glands and 15 (2.4%) from the thyroid glands, with the remaining 550 (88.9%) involving the skin and subcutis, muscle (n = 1), salivary glands (n = 4), lips (n = 2), ears (n = 4) and peripheral lymph nodes (n = 23). Most of the samples were neoplastic, with 99 masses classified as epithelial in origin, 347 as mesenchymal, 23 as round cell, five as melanocytic and eight as unclassified malignant neoplasms. Lipomas were the most common neoplasm diagnosed, accounting for 286 of all samples submitted.

Histopathological evaluation of the adrenal glands in a cat with primary hypoadrenocorticism and multiple endocrine disease.

Case summary: A 6-year-old male neutered domestic longhair cat was referred for investigation of weight loss, hyporexia, vomiting and diarrhoea. The cat was diagnosed with primary hypoadrenocorticism, exocrine pancreatic insufficiency, cobalamin deficiency and a chronic enteropathy, and started on therapeutic treatment. Diabetes mellitus developed 4.5 months later, and the cat was started on insulin therapy. The cat was euthanased 10 months following the diagnosis of hypoadrenocorticism due to the development of status epilepticus, which was not associated with glucose or electrolyte abnormalities. Histopathological assessment of the adrenal glands at post-mortem examination documented lymphoplasmacytic adrenalitis, with the lymphocytic population being predominant. Immunohistochemical staining classified the lymphocytic infiltrate as T-cell rich, supportive of the cat's hypoadrenocorticism being due to autoimmune disease. Relevance and novel information: This case documents the novel use of immunohistochemical staining in combination with histopathology to further assess the adrenal glands in non-neoplastic-associated primary hypoadrenocorticism in a cat. This identified similar pathological changes to those previously described in dogs with autoimmune primary hypoadrenocorticism. Additionally, this is the first report of a cat with multiple endocrine disease that included primary hypoadrenocorticism and highlights that monitoring for the development of additional endocrine disease should be advised in these cases.

Ocular mycobacterial lesions in cats.

Ocular mycobacterial infections are an under-recognized cause of morbidity in the domestic cat. This study aimed to explore the distribution, histopathological appearance, and severity of feline ocular mycobacterial lesions, and to characterize the immune cell population with immunohistochemistry. Routine histological staining with hematoxylin and eosin, and Masson's trichrome, was performed to identify ocular lesions and assign an inflammation score based on the number of cells present. Acid-fast bacilli were detected with Ziehl-Neelsen, and immunohistochemistry for ionized calcium-binding adaptor protein-1 (Iba1), calprotectin, cluster of differentiation 3 (CD3), and Pax5 was undertaken on formalin-fixed paraffin-embedded tissue samples from 24 cases of ocular mycobacteriosis. Posterior or panuveitis with concurrent retinitis was identified in 20/24 cases (83%), with retinal detachment in 16/20 (80%) of these cases. Choroidal lesions had the highest median inflammation score. Ziehl-Neelsen-positive organisms were detected in 20/24 cases (83%), with the highest prevalence of acid-fast bacilli detected in choroidal lesions (16/20, 80%). Lesions were typically granulomatous to pyogranulomatous, characterized by abundant numbers of Iba1-positive macrophages, followed by calprotectin-positive granulocytes and monocytes, fewer T cells, and rarer B cells. However, where iritis was identified, inflammation was typically lymphoplasmacytic (11/16 cases, 69%). Where diagnostic testing was performed, tuberculosis (ie, infection with Mycobacterium bovis, Mycobacterium microti, or a nonspeciated Mycobacterium tuberculosis-complex pathogen) was diagnosed in 20/22 cats (91%), with Mycobacterium lepraemurium infection identified in the other 2/22 cats (9%). These results suggest the choroid is the primary site of lesion development in most cases of feline ocular mycobacteriosis, and inflammatory changes are associated with the presence of mycobacteria localized to ocular tissues.

Necropsy findings in a cat with diabetes mellitus and heart failure.

CASE SUMMARY: A 7-year-old male neutered domestic shorthair cat, previously diagnosed and treated for diabetes mellitus (DM), subsequently presented in heart failure (HF). Echocardiography revealed biatrial and biventricular dilation with poor myocardial function, and a left atrial-to-aortic ratio of 1.95:1. There was caudal vena cava dilation, hepatomegaly and ascites. The HF was treated with furosemide for 5 weeks, but thereafter the cat presented recumbent and moribund, and was euthanased. Post-mortem findings included dilation of all four cardiac chambers with an increased heart weight. Microscopic examination of the heart revealed mild, predominantly interstitial or perivascular fibrosis throughout most of the myocardium, with small-to-medium-sized foci of replacement fibrosis within the left ventricular free wall and interventricular septum. There was evidence of myocyte degeneration, but myofibre disarray was mild and there was minimal evidence of inflammation. RELEVANCE AND NOVEL INFORMATION: Cardiac disease is common in cats and while HF is less common, it is a frequent cause of clinical signs and death. DM is a relatively common feline endocrinopathy. This case report describes DM and HF presenting as comorbidities, including detailed ante- and post-mortem findings. The case, and the epidemiology of these conditions, raise the question of whether a form of diabetic cardiomyopathy exists in cats, as it appears to do in humans.

A case of an intramural, cavitated feline gastrointestinal eosinophilic sclerosing fibroplasia of the cranial abdomen in a domestic longhair cat.

CASE SUMMARY: A 5-year-old neutered male domestic longhair cat was presented for the investigation of a cranial abdominal mass following a 1-month history of inappetence and lethargy. Abdominal ultrasound revealed a large cavitated mass confluent with the mesenteric aspect of the descending duodenum. At surgery, the mass was found to involve the pylorus, proximal duodenum and pancreas, and was non-resectable. Histopathological examination of surgical biopsies revealed a non-neoplastic process involving eosinophils and fibroplasia. RELEVANCE AND NOVEL INFORMATION: This case report describes an uncommon feline gastrointestinal pathology with an unusual appearance that may provide an additional differential diagnosis other than neoplasia or abdominal abscess when confronted with a cavitated abdominal mass in cats.

Prognostic factors and proposed grading system for cutaneous and subcutaneous soft tissue sarcomas in cats, based on a retrospective study.

OBJECTIVES: The objectives of this study included utilising a large database from a diagnostic laboratory to identify any breed, sex or age predilections for cutaneous and subcutaneous soft tissue sarcomas (STSs), and the most common anatomical locations. The second aim was to obtain clinical outcomes and to assess histological features of those tumours to identify any potentially useful prognostic indicators and propose a grading system. METHODS: Records from the laboratory were searched for feline submissions received from January 2012 to December 2013 diagnosed with STSs; the breed, age, sex and neuter status of the cat and anatomical location of the tumour were recorded. Clinical outcomes were acquired using a questionnaire to submitting practices, and histological features of tumours from patients with known outcomes were assessed. RESULTS: No sex, neuter status or breed predispositions were found. Most STSs arise in middle-aged and older cats, and the most common anatomical location was the trunk. Forty-seven cases had a known clinical outcome and archived tissues allowing for histological assessment of the tumour. Significant differences in median survival time (MST), mitotic index and histological score were detected between those cats that died of tumour-related disease and those that did not. A novel grading system applied to these tumours produced significant differences in MST between cats with low (MST = 900.5 days), intermediate (MST = 514 days) and high grade tumours (MST = 283 days). CONCLUSIONS AND RELEVANCE: This is the first study applying a histological grading system to these common tumours. Local recurrence is often the cause of a poor outcome, with metastatic disease apparently rare. The proposed grading system incorporates features that can be assessed on routine haematoxylin and eosin-stained sections; in this small study, the histological grade of the tumour appears to be associated with survival time.

A retrospective study of more than 400 feline nasal biopsy samples in the UK (2006-2013).

OBJECTIVES: The main objective of this study was to utilise a large database from a UK-based, commercial veterinary diagnostic laboratory to ascertain the prevalence of different forms of nasal disease within the feline population. Further objectives included using this database to detect any breed, sex or age predilections, or associations between the degree of brachycephalism, and the different conditions diagnosed. METHODS: Records from the laboratory were searched for feline submissions received between 31 May 2006 and 31 October 2013. For all samples taken from the nasal cavity, the diagnosis was recorded together with the breed, age, sex and neuter status of the cat, whether the clinical presentation was uni- or bilateral and whether a nasal discharge was present. Pedigree breeds were further subclassified according to skull conformation into brachycephalic, mesocephalic and dolichocephalic. Logistic regression models were constructed to assess the adjusted magnitude of association of significant risk factors with each disease, and each disease was also used as a potential independent risk factor for each other disease. RESULTS: The most prevalent nasal disease was rhinitis, followed by neoplasia and polyps. The most commonly diagnosed neoplasm was lymphoma, followed by adenocarcinoma and undifferentiated carcinoma, with benign tumours being very uncommon. No significant association was found between skull conformation and nasal diseases. The only statistically significant association was polyps being more likely to arise in younger male cats, with a mesocephalic skull conformation and no nasal discharge. CONCLUSIONS AND RELEVANCE: No significant association was found between skull conformation and nasal diseases, contrary to what might be expected. The only significant association found between any of the potential risk factors and various forms of nasal disease was polyps being more likely to arise in younger cats; other identified associations are only likely to be weak.

Spindle cell sarcomas, suggestive of peripheral nerve sheath tumours, arising in the tongues of two cats.

CASE SUMMARY: Two domestic shorthair cats, one an 11-year-old female neutered cat and the other a 13-year-old male neutered cat, presented with partly raised, well-demarcated masses at the rostral tip of the tongue. Histological examination and immunohistochemical staining were consistent with sarcomas, and were most suggestive of peripheral nerve sheath tumours. One tumour had histological features consistent with a malignant peripheral nerve sheath tumour (PNST). RELEVANCE AND NOVEL INFORMATION: Feline PNSTs arising on the tongue are rarely described in the published literature, and, to our knowledge, a case of malignant PNST originating at this site has not been described to date. Therefore, this represents a new differential diagnosis for cats presenting with a lingual mass. Regardless of histological malignancy, in cats these tumours have the potential for local recurrence but appear very unlikely to metastasise.

Nonocular Melanocytic Neoplasia in Cats: Characterization and Proposal of a Histologic Classification Scheme to More Accurately Predict Clinical Outcome.

Nonocular melanocytic neoplasia is considered uncommon in cats yet is routinely encountered in diagnostic pathology and recognized to exhibit a wide variation in biological behavior. Accurate prediction of clinical outcomes is challenging with no widely recognized prognostic criteria. Signalment and tumor location were retrospectively evaluated in 324 cats diagnosed with nonocular melanocytic neoplasia. Histologic features were described in 141 neoplasms and outcome data were available in 79 cases. Immunohistochemistry using Melan-A, PNL-2, cyclooxygenase 2 (COX-2), and E-cadherin was performed in a subset (n = 24). Multivariate analysis identified tumor site, mitotic count, and the presence of intratumoral necrosis to be independent predictors of tumor-related death. On the basis of these findings, we propose a novel histologic grading scheme in which nonocular melanocytic neoplasms involving the lips, oral or nasal mucosa, or nasal planum are considered high grade if they fulfill 1 or both of the following criteria: at least 4 mitoses in 10 high-power fields (HPF) or presence of intratumoral necrosis; those arising elsewhere are considered high grade if they fulfill both of the above criteria. Of 79 tumors with outcome data, 43 (54%) were low grade and 36 (46%) were high grade. The grading system had an 80% sensitivity and 92% specificity for predicting tumor-related death in this population of cats. Median survival for cats with low-grade tumors was not reached, and the median survival was 90 days for those with a high-grade tumor. PNL-2 and Melan-A were sensitive markers for feline nonocular melanocytic neoplasia, and although not significantly associated with prognosis, a large proportion expressed COX-2, suggesting a potential therapeutic role for COX-2 inhibitors.

Retrospective study of more than 9000 feline cutaneous tumours in the UK: 2006-2013.

Objectives The aim of the study was to utilise a large database available from a UK-based, commercial veterinary diagnostic laboratory to ascertain the prevalence of different forms of cutaneous neoplasia within the feline population, and to detect any breed, sex or age predilections for the more common tumours. Methods Records from the laboratory were searched for feline submissions received between 31 May 2006 and 31 October 2013. For masses arising within the skin for which histopathology had been performed, the diagnosis was recorded together with the breed, age, sex and neuter status of the cat. Odds ratios for breed predisposition to skin tumours overall, to histologically malignant tumours and to the more commonly occurring tumours were calculated, with the non-pedigree cat population as the control. Results Of the 219,083 feline samples submitted, masses arising within the skin comprised 4.4% and there were 89 different diagnoses recorded for these masses. Just 6.6% of these cases were non-neoplastic in nature, and, of neoplastic masses, 52.7% were considered histologically malignant. The 10 most common skin tumour types accounted for 80.7% of cases, with the four most common being basal cell tumours, fibrosarcomas, squamous cell carcinomas and mast cell tumours. Conclusions and relevance Despite the large number of different diagnoses in this study, a relatively small number of tumour types accounts for the majority of skin masses occurring in cats, most of which are neoplastic in nature. There are a number of breed predispositions for the more common tumour types, although no pedigree breed had increased odds of developing a malignant tumour compared with the non-pedigree cat population; several breeds had significantly decreased odds. Just over half of the neoplastic masses in this study were considered histologically malignant.

Clinical, histological and prognostic features of a novel nail-bed lesion of cats: 41 cases.

Objectives There is a distinct subset of lesions arising on the digits of cats, located at or close to the nail-bed epithelium, which are typically composed of proliferative fibroblast-like cells, multinucleate giant cells and areas of osseous metaplasia, but currently there is no published literature detailing the clinical or histological features of these lesions. Methods This study identified 41 such cases from two large commercial diagnostic laboratories and assessed various histological and clinical features; 22 cases had additional follow-up data available. Results All masses in this study were exophytic, variably inflamed, contained large numbers of spindle cells and had areas of capillary formation. The majority also had areas of ulceration, multinucleate giant cells and osseous metaplasia. The mitotic count was variable, but mitoses were confined to the fibroblast-like cells. Male cats appeared predisposed and the second digit was the most commonly affected. Conclusions and relevance These distinctive lesions arising on the digits of cats had potential for local recurrence but metastasis was not reported. Based on these clinical and histological features, the masses in this study appear most similar to giant cell reparative granulomas, and trauma, injury to the nail or nail-bed and nail-bed infections may potentially contribute to their development.

Selective fatty replacement of the exocrine pancreas in a domestic shorthair cat: histopathological findings with long-term outcome.

The clinical, histopathological findings and eventual outcome of a cat with marked and selective fatty replacement of the exocrine pancreas are described in this case report. A 9-year-old female neutered domestic shorthair cat presenting with polyphagia, weight loss and intermittent vomiting was diagnosed on histopathology with severe exocrine pancreatic atrophy, with relative sparing of the endocrine pancreas and replacement of the acinar cells by mature adipose tissue. This case report discusses the histological findings in this case and the eventual outcome, as well as the potential underlying causes of this histological change.

Feline cutaneous mast cell tumours: a UK-based study comparing signalment and histological features with long-term outcomes.

Feline cutaneous mast cell tumours (MCTs) are the second most common skin tumour in cats; but, unlike in dogs, there is currently no histological grading system for this type of tumour. This study recorded the signalment and anatomical location from a total of 287 records from MCTs submitted to a UK commercial diagnostic laboratory. Questionnaires to submitting practices were used to obtain follow-up data, and the histological features of 86 tumours were evaluated from 69 cats with a known outcome. Twelve of the 69 cats (17.4%) died of MCTs, with significantly lower survival times. The median age of cats presenting with MCTs was 11 years (range 5 months-19 years), with no sex or neutered status predilection. Some pedigree breeds were more susceptible to MCTs, particularly the Siamese, Burmese, Russian Blue and Ragdoll. The head was the most common site in younger cats, compared with the trunk in older cats. The number of tumours had no effect on survival. A new subcategory of well-differentiated MCTs with prominent multinucleated cells is described, and three of the five cats with this novel form died from MCT-related disease. There was an association between mitotic index and survival time. However, there was no significant association between histological type and survival.

Disseminated lipid-rich peritoneal mesothelioma in a horse.

A 9-year-old Haflinger mare presented to the Liphook Equine Hospital with a history of weight loss, azotemia, and repeated episodes of ascites over a period of 10 days. The horse was euthanized after exploratory laparotomy revealed large numbers of variably sized masses distributed throughout the peritoneal cavity. Macroscopically, some masses were papillary, while others were nodular. Histologically, the masses were comprised of large to giant, variably shaped, and occasionally multinucleated neoplastic cells with marked anisokaryosis and anisocytosis and a high mitotic rate. Small to moderate numbers of neoplastic cells were swollen by 1 to several, moderately sized to large, clear, circular or ovoid vacuoles, which stained positive with oil red O. Immunohistochemically, the neoplastic cells co-expressed vimentin and cytokeratin. Electron microscopy demonstrated tumor cells with tight junctions, microvilli, and numerous intracytoplasmic lipid droplets. These findings are consistent with a lipid-rich form of mesothelioma, which should be considered as a differential diagnosis if lipid vacuoles are present in potentially neoplastic cells in equine abdominocentesis samples.

Cattle Ly49 is polymorphic.

Cattle are the only non-primate species to have an expanded KIR gene family. In addition they have a single Ly49 gene, thought to be monomorphic. We have identified two additional Ly49 cDNA sequences in cattle that encode molecules predicted to differ by 14 and 16 amino acids from the original sequence. All available data indicate the presence of only one Ly49 gene in cattle, thus the divergent sequences reported here may represent ancient allelic lineages, a high level of polymorphism in an ancestral gene or a previously expanded and subsequently contracted Ly49 gene family. Cattle are the only species known to have an expanded polymorphic KIR gene family and a polymorphic Ly49 gene.