Case Study – Equine Juvenile Mandibular Ossifying Fibroma
In July this year we were asked to examine a weanling thoroughbred foal called Marilyn that was found to have a growth on her mandible just inside her lower lip. The growth was firm and ulcerated however there was no pain associated with it on palpation. The owner had noticed the growth by chance as there were no major outward signs of the growth or of an illness and she was doing well otherwise. We decided to x-ray the head to help us with our diagnosis.
X-rays revealed a large bony growth extending from the most rostral part of the mandible. It seemed to be of similar consistency to the normal bone of the mandible and wasn’t originating from a tooth root as many of these facial growths can. At this stage we began to do some research and a tentative diagnosis of Equine Juvenile Mandibular Ossifying Fibroma (EJMOF) was established.
Equine Juvenile Ossifying Fibroma is a benign tumor that develops from the intramembranous bone of the mandible (lower jaw).
Equine Juvenile Ossifying Fibroma is a benign tumor that develops from the intramembranous bone of the mandible (lower jaw). The tumor has a high occurrence in young horses aging from 2mths to 14mths of age, it has no breed or sex predilection and it is unsure as to whether it can be passed on through genetics. They are known to be locally aggressive; invading the surrounding bone of the mandible and disrupting the normal trabecular structure of the bone. The origins of the tumors are unknown. Trauma is often associated with the findings however it is unknown whether the trauma comes first, and the tumor then proliferates or whether the tumor is present first and makes the mandible bone more brittle and open to damage.
Marilyn was referred to our partner clinic at the Ballarat Veterinary Practice. They took sample of the tumor and confirmed that we were in fact correct with our tentative diagnosis! The best treatment for these tumors is complete excision with wide margins in order to prevent reoccurrence. Due to the location and the size of the tumor this meant Marilyn had a mandibulectomy performed, which basically meant she had a large portion of her lower jaw removed.
The second x-ray shows the large portion of Marilyn’s mandible that was removed. She has since been back home and is doing well.
She has had follow up x-rays to check for any reoccurrence of the tumor but so far, they have been all clear. The obvious effect of this surgery is the need to relearn how to eat without the help of a lower jaw.
Marilyn seemed to get to grasp with this quite quick and has since been eating well. She will require plenty of monitoring and wouldn’t cope very well in a paddock with short grass and so must always have supplemental feeding if that is the case. The other thing that will have to be considered is her future racing career. Without most of her lower jaw keeping a bit in her mouth may be difficult however there are certain types of gear that may work if she has trouble. It’s worth noting that there was a race horse a couple of spring carnivals ago that came out from Japan as a companion racehorse that had its mandible resected for the same reason as Marilyn. The horse was able to compete at the highest level of racing post surgery.
One last side effect of not having lower incisors is that she now sticks her tongue out at everybody so watch out for this cheeky face in the mounting yard one day!
