Multilobular tumor of bone (MTB), also known as multilobular osteochondrosarcoma (MLO), is a relatively uncommon, slow-growing but potentially malignant tumor chiefly affecting the skull bones in dogs, with occasional reports in cats and horses. Characterized by its local aggressiveness and variable malignancy, MLO can cause compression-related symptoms due to adjacent organ involvement, particularly in the brain. Despite potentially challenging treatment and a risk of local recurrence and metastasis, long-term control and survival are possible, especially with histologically complete surgical resection.
On this page:
Terminology
Previously known by various names such as chondroma rodens and multilobular osteoma, the term Multilobular tumor of bone is now preferred. This designation acknowledges both its potential malignancy and distinction from similar human conditions while capturing its multilobular structure involving bone and cartilage.
Epidemiology
Domestic dogs, particularly middle-aged to older and medium to large breeds, most commonly develop MLO. The median age of affected dogs is around 8 years. Cats and horses are much less frequently afflicted, with documented cases being sporadic.
Risk Factors
Middle to older age in dogs.
Medium to large dog breeds, with a median weight of 29 kg in affected canines.
Associations
No strong breed or sex predilection noted.
Clinical Presentation
MLO typically presents as a firm, immovable mass at the calvarium, zygomatic arch, orbit, maxilla, mandible, or tympanic bulla. Symptoms relate to compression of adjacent structures, often causing neurological deficits or other organ-specific signs without necessarily indicating the full extent of tumor invasion.
Pathology
MLO originates from fibrous or cartilaginous tissue and exhibits a nodular pattern with islands of bone or cartilage delimited by fibrous septae.
Location
Most commonly involves the skull, but cases in the pelvis, ribs, and spine have been reported. The bones of the skull most often affected are the temporal and parietal region, orbit, hard palate, mandible, and tympanic bulla.
Classification
A histologic grading system is utilized, reflecting the tumor's potential for local recurrence and metastasis.
Macroscopic Appearance
Visible as a stippled mass on the skull with gritty foci intersected by fibrous bands and surrounded by a tough fibrous membrane.
Microscopic Appearance
Distinguished by circular, oval, or irregular nodules of cartilaginous or bony tissue with fibrous septa, mesenchymal zones, and spindle-shaped cells.
Radiographic Features
General radiographic characteristics include a granular mineral opacity, well-defined tumor margins, and adjacent bone lysis.
Radiography
Shows a stippled or granular appearance with sharp demarcation from surrounding bone.
CT
Demonstrates a coarse, granular mineral density, often with lytic changes in underlying bone and brain compression, which helps in surgical planning.
MRI
Reveal heterogeneous signal intensity on T1 and T2-weighted images with areas of contrast enhancement that define the extent of tumor invasion into soft tissues and brain.
Radiology Report
Include the following in a radiology report:
Morphology
Describe tumor size, shape, and borders.
Relationship to/involvement of
Specify relationships to adjacent skull bones and brain structures.
Extension
Note any invasion into the brain, calvarium, or orbit.
Treatment and Prognosis
Standard treatment involves surgical resection, which may be curative, especially when complete margins are achieved. Adjuvant radiotherapy may be considered in cases of incomplete resection. Histologic grade is a strong prognostic factor, with a higher likelihood of local recurrence and metastasis in Grade III tumors. While metastasis commonly occurs in the lungs, dogs may remain asymptomatic for extended periods.
Complications
Local recurrence (47-58% rate).
Metastasis, primarily in the lungs (20-58%).
History and Etymology
The term "multilobular" reflects the characteristic multi-lobed pattern of tissue growth, which distinguishes it from other types of bone tumors.
Differential Diagnosis
Osteosarcoma.
Chondrosarcoma.
Other bone or skull tumors.
Differences are typically based on histological examination and imaging characteristics.
Practical Points
Obtain complete surgical margins when possible to lower recurrence risk.
Consider adjuvant therapies for incomplete resection.
Histologic grade significantly impacts prognosis and treatment decisions.
Regular monitoring for metastasis and local recurrence is essential post-treatment.
Unable to process the form. Check for errors and try again.