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  Discussion on Fibrous dysplasia
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Member:
digger89

Posted on Thursday, Jun 11, 2009 - 6:02 pm:

My 20 year old quarter horse had a large egg- shaped bony lesion removed from his hind canon/splint bone, and the path report came back fibrous dysplasia. I can't find much info about this except it usually occurs in the jawbones of young horses. My vet doesn't know much about this either. Has anyone else seen this type of tumor? Thanks. Sarah
Moderator:
DrO

Posted on Thursday, Jun 11, 2009 - 8:17 pm:

Hello SarahS,
I am afraid the description it is not very helpful. It means the tissue was an unusually large piece of mature fibrous tissue. It does not tell us why this occurred. Is there history or more findings that might help?

Fibrous dysplasia can be associated with early cancers but it may be also associated with chronic inflammatory conditions. In humans there is a condition where bone is replaced with this dysplastic fibrous tissue and can be either a focal condition or generalized effecting many bones. My understanding is the cause is unknown and there is no treatment. Such conditions have also been associated with endocrine diseases and toxicities but these cases are usually generalized.
DrO
Member:
digger89

Posted on Thursday, Jun 11, 2009 - 8:56 pm:

Thank you DrO. Digger had what looked like a splint on the inside hind, just below the hock. It has been there for several years but continued to grow slowly. It felt firm, only slightly tender to deep palpation, and non-movable. The xray was very interesting, showing what appeared to be a bony growth in the shape of a bell curve, with clear vascular channels in the center. It did not seem to have invaded the cannon bone or splint bone. When it was removed, the bulk of the tumor shelled out fairly easily but had long "tails" extending both up and down along the bone that were more difficult to remove. the surgeon said that the "tail" tissue was very rubbery and not calcified. The total length was approximately 5", with the central section about 1 1/2" wide and deep. To my knowledge Digger has never had an injury in that area.
Does this info help at all? Thanks. Sarah
Moderator:
DrO

Posted on Friday, Jun 12, 2009 - 7:24 am:

Yes to some degree but I do have trouble putting a name to what is happening or trying to guess if this is going to be the end of it. On the radiographs did the tumor seem to effect the character of the underlying bone? Did it seem to be invading the bone or possibly the bone was morphing to this fibrous type tissue?
DrO
Member:
digger89

Posted on Friday, Jun 12, 2009 - 7:51 pm:

DrO - I actually got a copy of the path report which I am including here. It did seem to suggest that it could recur. Another case report was mentioned but I do not have access to that journal. Apparently this is quite rare, and the pathologists were very excited and wanted to see the pre-op xray. It is never good to be an "interesting" patient.....

New Bolton Center
Digger; Mammalian - Equine / horse - Horse - American Quarter; Gelding; Adult 20 Years
History
Slowly growing mass on right hind medial aspect of metatarsus. DDx: osteoma, calcicosis circumscripta.
Diagnosis
Fibrous dysplasia
Comments
Due to the degree of palisading of the spindle cells and the predominance of the storiform pattern, immunohistochemistry
was performed to rule out a peripheral nerve sheath tumor; the spindle cells showed no immunoreactivity to S-100, a
neural marker.
This lesion is consistent with fibrous dysplasia, which is a very rare skeletal developmental anomaly thought to result
from a congenital mesenchymal defect that manifests as a local defect in osteoblast differentiation and maturation. In
humans, fibrous dysplasia can be a monostotic or polyostotic lesion, typically affecting long bones; however craniofacial
manifestations are reported. The lesion is characterized by a slowly expansile lesion within the medullary cavity that can
eventually deform the bone and cause pain or pathologic fracture. Fibrous dysplasia is extremely uncommon in animals;
however there is a recent report of a case in a horse that arose from the accessory carpal bone (Jones et. al. Equine
Veterinary Journal 2004, Vol. 36(1), pp.93-95). Surgical recurrence can occur due to the difficulty in obtaining clean
margins. Rare neoplastic transformation is reported (0.4-1% cases in humans), but this has not been reported in
animals.
Pathologic Anatomic Findings
Third metatarsal bone (right hind): fibrous dysplasia
Lab Findings
Histopathology
Test Level Result: Necropsy / Biopsy - Slides(H & E)(Slide Preparation)
Multiple sections through the mass are examined and the lesions are similar. The tissue is composed of a moderately
dense proliferation of spindle-shaped cells arranged in interwoven bundles and streams with frequent storiform
patterns and a moderate to abundant amount of dense collagenous matrix. Spindle cells have indistinct cell borders,
a moderate amount of eosinophilic fibrillar cytoplasm and an oval nucleus with coarsely stippled chromatin. Where
the spindle cells are arranged in a storiform pattern, cells often palisade around central collagenous matrix, frequently
with a central mineralized round to irregular bone spicule. There is an abrupt transition between the collagenous
stroma and the foci of bone, without a layer of osteoblasts lining the bone spicule. Occasional multinucleate
osteoclasts are associated with the bone tissue. Surrounding the spindle cell proliferation, there are few islands of
pre-existing lamellar bone and a thick layer of dense fibrous connective tissue.
Sample Test Name
Slide - 1
Other (per slide) (Immunohistochemistry (IHC))
S100 antigen expression is not detected with the cell population. Positive and negative controls were utilized
and worked appropriately.
Moderator:
DrO

Posted on Monday, Jun 15, 2009 - 8:10 am:

That helps Sarah, and how about the bone on radiographs does it now look normal?
DrO
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