RUIN is an abbreviation for RadioUlnar Ischemic Necrosis. This name is given to a group of diseases that causes destruction of the radius and ulna bones.
The characteristic finding on x-rays or CT scan is permeative destruction of bone which extends from the interosseous ligament region into the radius, ulna or both bones. The location of the lesion is typically where the artery in vein enters the proximal third of the radius and ulna bones.
There are a variety of causes of RUIN. Sometimes it is caused by vascular tumors that originate from this site or tumors that have spread to this area. The most common tumor to cause RUIN is hemangioma, which is a benign tumor. Hemangiosarcoma, a highly malignant tumor, is a known cause of RUIN, but is less common. Metastatic adenocarcinoma has also been reported. We have also seen a RUIN lesion in a Rottweiler due to metastatic osteosarcoma.
Another uncommon cause of a RUIN lesion is due to a fungal infection called Coccidiomycosis.
A presumptive diagnosis can be made based on x-rays, CT scan or MRI. Diagnosis of this condition requires a biopsy. This can be done with fine needle aspiration under fluoroscopic or radiographic guidance. Because these lesions are not very large, it may be difficult to successfully collect a representative sample with a needle. Alternatively, a surgical biopsy can be done with submission of the abnormal tissue for histopathology.
If the lesion is significantly large, it may weaken the bone and cause a fracture. Bone grafting of the region may be indicated. Since getting a good biopsy usually involves an open approach, we recommend scraping the affected areas, and packing the defects in the bone with bone graft to stimulate healing. If there is significant weakening of the bone, placement of a plate on weakened bone(s) may be indicated. If the lesion is caused by a tumor, segmental resection of the affected of ulna bone may be possible. If the tumor is more extensive, amputation of the limb may be indicated. If the tumor is caused by spread of cancer from another region of the body, the prognosis is very guarded and consultation with a medical oncologist should be made. Amputation of the limb should not be done in such cases.
Dr. Roy Pool from Texas A&M University, College of Veterinary Medicine is an excellent reference for unusual bone lesions such as RUIN.