Post ovulation hematoma
Keywords: hematoma, ovary, ovulation. mare, equine
The reproductive tract from a Standardbred mare that was estimated to be approximately 10 years of age (using dental aging). It was donated with no medical history. An incidental finding at post-mortem was this large ovarian hematoma in the left ovary and a smaller one in the right ovary.
The image below shows the left and right ovaries opened. A fragmented coagulum has been removed from the left ovary. The other coagulum remains in situ in the right ovary. The inset image allows a closer view of the right ovary.
Essentially, histology of the left ovary showed a coagulum containing scattered lymphocytes, plasma cells and pigment laden macrophages in the periphery of the hematoma. This pigment was probably hemosiderin. In the right ovary, histological evidence indicated that the hematoma was more acute that that in the left ovary. There was no evidence of neoplasia.
A granulosa cell tumor (GCT) would be unlikely in this case because the contralateral ovary was still active with follicle development at the time of death. In the case of a GCT, the tumor usually produces inhibin which suppresses FSH production and in turn, suppresses ovarian activity in the contralateral ovary.
Note: Although this hematoma is large, they may be almost twice this size. Post ovulation hematomas are not uncommon yet little is known about them. Why they form in apparently normal mares is not known. There are no data to substantiate that they have no effect on fertility yet anecdotally, that appears to be so. They also appear to have no effect on reproductive behavior. The only pathology associated with these hematomas is in rare cases, mild colic and interference with gastrointestinal tract when they become very large. Perhaps the greatest problem they cause is unnecessary surgery when they are mistaken for GCTs!
The image below (not from the case featured in this entry) shows the typical appearance of a post ovulation hematoma.
Image size: 640 x 480px
Together with continuing ovarian activity in the contralateral ovary, the echogenic fibrin network usually distinguishes a hematoma from a GCT. However, these are not an infallible diagnostic features because some GCTs may resemble ovarian hematomas and there can be remarkable contralateral ovarian activity in some mares with GCTs.
Eventually the affected ovary will return to its normal size but this may take several months to occur.
