Case series summary: A queen, tom and four 1-year-old female offspring presented for routine neuter. Two of the littermates (cats 1 and 2) were diagnosed with a uterine abnormality during surgery. The left uterine horn of both cats appeared as a thin, solid, cord-like structure, whereas the right uterine horn of both cats appeared to have intermittent bulges consistent with pregnancy. The two other littermates, queen and tom were reproductively normal. The uteruses of the affected cats were nearly identical with a gross and histopathologic diagnosis of uterus unicornis with concurrent pregnancy. Ovaries were present, bilaterally. An oviduct was present only on the single normally developed and pregnant uterine horn in both cats. At a postoperative follow-up evaluation, abdominal ultrasound was performed on the two cats with uterine abnormalities. Cat 1 was ultrasonographically within normal limits. Cat 2 was diagnosed with ipsilateral renal agenesis on the same side as the absent uterine horn.
Relevance and novel information: The complexity of uterus unicornis and renal aplasia is demonstrated by this unique presentation of five related cats for ovariohysterectomy. This report raises questions regarding the genetic, environmental, hormonal or other underlying causes of this anatomic abnormality in cats that may spur additional research. This is the first publication describing uterus unicornis in gravid feline littermates, with one of the cats having ipsilateral renal agenesis. This is also the first publication to describe oviduct agenesis on the affected uterine horn in feline uterus unicornis.