Granulosa Cell Tumors

By Jos Mottershead

"Granulosa-thecal cell" or "granulosa cell" tumors (GCT's) are one of the most common ovarian tumors to be found in equines.

Granulosa cell tumors are usually benign steroid-producing tumors that may grow very large. A Granulosa Cell Tumor, with a ruler indicating it's sizeOften they are initially found during a routine reproductive examination of the mare, when one ovary is discovered to be excessively larger than the other. The tumor shown at left is six inches in length, but larger examples are found. Typically the opposite ovary is found to be small and displaying no follicular activity.

A GCT may also be suspected if the mare's attitude suddenly changes. For example she may become very "studdy", displaying stallion attitudes and postures, and may become aggressive, and even start to develop the typical stallion cresty neck. This is as a result of the granulosa cell tumor secreting testosterone. Alternatively, she may display continuous estrus ("nymphomania"), or even only very occasional estrus.

GCT being removed through a flank incisionConclusive diagnosis of a GCT can be difficult to determine, except as a result of a collection of findings. Ultrasound, which may initially appear to be a sensible diagnostic tool to use, is actually frequently not of great assistance, other than indicating that the affected ovary is of excessive size. It should be noted that there are ovarian conditions other than GCT's that may present similarly per ultrasound, especially annovulatory hemorrhagic follicles. Combined blood-inhibin and testosterone assays have recently proven reliable for diagnosis of GCT's.

Treatment of granulosa-thecal cell tumors is achieved by removal of the affected ovary and the tumor. A return to reproductive normality may be expected six to twelve months after surgery. Removal can be carried out trans-vaginally or through a flank incision (seen at right), depending upon the size of the tumour, and other circumstances.

GCT cut in half, showing the definitive honeycomb effect



When cut in half, the GCT exhibits a definitive "honeycomb" pattern on the interior, as seen here on the left.



All photos on this page courtesy of Terry Ready of Oakwood Quarter Horses, the attending anesthesiologist for the surgery.

© 2000 Jos Mottershead and
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