BackgroundChronic hepatitis (CH) occurs commonly in dogs but is associated with a variable and largely unpredictable prognosis. p21, a cell‐cycle inhibitor and marker of cellular senescence, is upregulated in human liver disease and is a better prognostic marker than histological or clinical scoring systems.ObjectiveTo quantify hepatocyte p21 immunopositivity in histopathology samples from dogs with CH and determine its association with outcome.AnimalsTwenty‐six client‐owned dogs with histologically confirmed CH, and 15 dogs with normal liver histology.MethodsMedical records and liver histopathology samples were retrospectively reviewed to identify cases of CH. Immunohistochemistry for p21 was performed on all samples and hepatocyte immunopositivity was visually quantified. Relationships between p21 and dog age and dog survival time were statistically evaluated.ResultsHepatocyte p21 immunopositivity in dogs with CH was high (median percentage of positive hepatocytes: 90%, range: 20%‐98%) and exceeded 70% in 23/26 cases with no association with age. In control dogs, p21 immunopositivity was low (≤15% positive hepatocytes in 12/15 cases) and was positively correlated with age (r s = 0.63; P = .011). Dogs with p21 immunopositivity exceeding 91.8% (upper tercile) had significantly shorter survival compared to dogs with less than 88.9% immunopositivity (lowest tercile; 218 versus 874 days, P = .006). Increasing hepatocyte p21 immunopositivity was significantly negatively associated with survival time (HR 4.12; 95% CI 1.34‐12.63; P = .013).Conclusions and Clinical ImportanceMarked p21 immunopositivity in dogs with CH might be indicative of widespread hepatocellular senescence. A significant association with survival time also suggests a potential value for p21 quantification in determining prognosis.

The incidence and range of spontaneous microscopic lesions were determined in the eyes of male and female control Sprague-Dawley and Han Wistar rats. Data were collected retrospectively from 1411, 817, 970, 658, and 3999 rats from control groups of 4-, 13-, 26-, 52-, and 104-week studies, respectively, carried out between 1997 and 2019. Microscopic lesions of the eye were rare in 4- and 13-week studies, uncommon in 26- and 52-week studies, and were of relatively higher incidence in 104-week studies. Neoplastic lesions were sporadic and were only observed in 104-week studies. In Sprague-Dawley rats, the most common lesions (>1% in 104-week studies) were retinal degeneration, retinal rosettes/folds, and lenticular degeneration. The Han Wistar rats presented a range of ocular lesions similar to the Sprague-Dawley rats. However, retinal degeneration occurred with an earlier onset and at higher incidences, ranging from >5% in 26-week studies up to 45.72% in 104-week studies. In both strains, females exhibited higher incidences and severities of retinal degeneration. It is hoped that reference to the incidences reported here will facilitate the differentiation of spontaneous lesions from test article–induced lesions in toxicology studies in these strains of rat.

Nodular fat necrosis is a rare condition in the cat, and no cases of free-floating abdominal masses in cats have been previously reported in the literature. Furthermore, nodular fat necrosis when present has not been associated with an acute abdomen presentation. An adult neutered female cat presented with acute abdomen. An exploratory laparotomy was performed identifying two free-floating masses within the abdominal cavity of the patient. These masses were removed and the patient made an uneventful recovery. The histopathological analysis of the two free-floating abdominal masses was consistent with a diagnosis of nodular fat necrosis. Acute abdomen is a rare presentation in the cat. When investigation highlights multiple abdominal masses without obvious communication with organs, nodular fat necrosis should be considered as a differential diagnosis. Surgical resection of these lesions was associated with a good outcome in this cat, with no signs of pain being present following surgical resection of the masses.

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