CLINICAL FEATURES

Signalment

•synonyms: multilobular tumor of bone, chondroma rodens, calcifying or juvenile aponeurotic fibroma, cartilage analogue of fibromatosis, and multilobular osteoma, chondroma, or OSA

•multilobular osteochondrosarcoma is an uncommon tumor attributable to abnormal cellular activity arising from the periosteum of bones formed by intramembranous ossification with the cells of origin periosteal cells of the common chondrocranium and viscerocranium, both of which share a common embryonic origin

•multilobular osteochondrosarcoma has a predilection for the skull of dogs with sites including the cranium (i.e., occipital, parietal, and frontal bones), orbit, zygomatic arch, mandible, and maxilla

•other sites includes pelvis, rib, and os penis

•median age 7.5-8.0 years

•median body weight 29 kg

•no sex or breed predisposition

•multilobular osteochondrosarcoma has also been diagnosed in other species including the cat, ferret, and horse

Clinical Signs

•palpable, fixed, and firm mass

•pain on mouth opening for tumors involving the mandible and zygomatic arch

•exophthalmos

•neurologic abnormalities for tumors involving the cranium

•dyspnea for tumors involving the tympanic bulla

DIAGNOSIS

Imaging

Survey Radiographs

•tumor borders are sharply demarcated with limited bone lysis and a course granular mineral density with a lobular pattern (= popcorn appearance with stippled and heavily calcified or ossified regions)

•lack of radiographic evidence of multilobular osteochondrosarcoma has been reported

Computed Tomography

•CT is indicated for detection of tumor calcification, cortical bone and soft tissue involvement, and intramedullary or intracranial extension to aide in surgical planning

•multilobular osteochondrosarcoma has a multilobular appearance with well-defined margins

•multilobular osteochondrosarcoma of the rostral skull and zygomatic arch has a coarse granular appearance

•multilobular osteochondrosarcoma of the caudal skull has a fine granular or stippled appearance

•majority of calvarial multilobular osteochondrosarcoma have significant intracranial involvement

•contrast enhancement is not helpful

Magnetic Resonance Imaging

•MRI is indicated for detecting extraosseous and intramedullary extension of skull tumors

•T1-weighted images: multilobular osteochondrosarcoma is hypointense compared to the brain, but not CSF, with a rim of contrast enhancement and areas of enhancement interspersed with areas of non-enhancement

•T2-weighted images: low signal intensity; enhancement is poor for areas of tumor consisting mainly of osteoid, despite marked vascularity and cellularity, while chondroid forming matrix has intense contrast enhancement

Histology

•histologic features: multiple lobules centered on a core of cartilaginous or bony matrix which is surrounded by a thin layer of spindle cells and separated by fibrovascular septa

•characteristic trilaminar appearance:

•central area of cartilage or bone that may be calcified or ossified

•middle zone of plump, spindle-to-ovoid shaped cells

•peripheral zone of fibrous tissue

•histologic indicators of malignancy include increased mitotic activity, necrosis, hemorrhage, loss of lobular architecture, and overgrowth of 1 of the mesenchymal elements

•histologic grading of multilobular osteochondrosarcoma is prognostic for local tumor recurrence, metastasis, and survival time

TREATMENT

Surgical Treatment

•surgical techniques: craniectomy, maxillectomy, mandibulectomy, hemipelvectomy, or rib resection

•cranioplasty, with either allograft of polymethylmethacrylate, has been described

•however, infection in prosthetic material can be devastating when used for calvarial reconstruction

•role of chemotherapy and radiation therapy is unknown

•complete response to samarium radiation therapy has been reported in 3 dogs

•pulmonary metastatectomy should be considered for pulmonary metastases due to slow growth rate

•postoperative neurologic recovery can take 1-2 weeks but majority of dogs return to normal

PROGNOSIS

Local Recurrence

•47%-58% local tumor recurrence rate with median time to local recurrence 426-797 days

•prognostic factors for local recurrence include surgical margins and histologic tumor grade:

•median DFI is significantly increased with complete resection (330 days v > 1,332)

•local tumor recurrence is significantly more likely with grade III multilobular osteochondrosarcoma (78% v 30% for grade I and 47% for grade II tumors)

Metastasis

•56%-58% metastatic rate with median time to metastasis 426-542 days

•metastatic sites include the lungs (90%), cerebral cortex, pancreas, kidney, mediastinum, and rib

•prognostic factors for metastasis include surgical margins and histologic tumor grade:

•metastasis is significantly more likely with incomplete resection (75% v 25%)

•metastasis is significantly more likely with grade III multilobular osteochondrosarcoma (78% v 30% for grade I and 60% for grade II tumors)

•survival times following detection of pulmonary lesions can be > 12 months

Prognosis

•MST 24 days for untreated multilobular osteochondrosarcoma

•MST 669-797 days for treated multilobular osteochondrosarcoma

•median time to death from recurrent or metastatic disease is 239 days

•prognostic factors: tumor site, histologic grade, and surgical margins

•MST for mandibular tumors is significantly better than other sites (1,487 days v 528 days)