Surgical Case Notes – Multilobular OsteochondrosarcomaDecember 18, 2018

Surgery Case Notes

Multilobular Osteochondrosarcoma in a Japanese Chin

Written by Chloe Wormser, DVM, DACVS

Case Summary

An approximately 15-year-old castrated male Japanese Chin was presented to the Diagnostic Imaging Service for a slow growing mass on the left side of his face which was first noticed 6 months prior.  The client reported the dog had become progressively more head shy due to the mass, and had a decreased appetite.  The dog had a history of bilateral blindness due to cataracts, but had otherwise been healthy. The physical exam revealed an approximately 6 cm x 6 cm hard, fixed, painful mass caudal to the left orbit, causing marked exophthalmos of the ipsilateral globe. The globe had an approximately 4mm x 3mm centrally located descemetocele and pinpoint corneal perforation.  Bloodwork (complete blood count and serum biochemistry) was normal aside from a mild elevation in alkaline phosphatase (356 U/L, reference range 20-150 U/L).  A CT scan of the skull and thorax was recommended for surgical planning and complete staging.

CT Scan Results

On the CT scan a multilobular, mixed soft tissue and bone attenuating mass measuring 6.1 cm x 6.1 cm x 5.7 cm was identified arising from the left zygomatic arch (Figures 1 & 2).  The mass had a “popcorn” architecture, invaded the caudal left orbit, and compressed the ramus and coronoid of the left hemimandible.  No evidence of cervical lymph node enlargement or pulmonary metastasis was seen.  Based on the classic CT appearance of the mass, a tentative diagnosis of multilobular osteochondrosarcoma was made. Local control options were discussed with the client, including surgical resection and radiation therapy.  The client elected to proceed with surgical resection of the mass along with enucleation of the ipsilateral eye, which was scheduled for the following week.

CT 1

Figure 1. Axial CT image of the skull showing a left sided, multilobular mass with “popcorn” architecture arising from the zygomatic arch.

CT Recom

Figure 2. CT reconstruction of the mass.


For surgery, the patient was positioned in right lateral recumbency. A routine left enucleation was performed.  An approximately 8 cm incision was then made directly over the mass.  The subcutaneous tissue and platysma were incised, and the mass was carefully dissected from the masticatory muscles using a vessel sealing device.  A sagittal saw was used to make osteotomies in the rostral and caudal zygomatic arch, and the mass was removed.  A closed-suction drain was placed in the surgical wound, and the incision was closed routinely.

The patient recovered smoothly and was discharged from the hospital 36 hours post-operatively.

Histopathology showed a completely excised multilobular osteochondrosarcoma with no cellular or nuclear atypia and a mitotic index of zero.   Given these results, no ancillary therapy was recommended.  Long-term monitoring for local tumor recurrence was discussed.

The patient went on to heal fully from surgery with no complications.  At 4 month-follow up, the client reported the patient had an excellent quality of life and comfort level.  The client was happy with the cosmetic outcome of the surgical procedure.  On examination, the patient had no evidence of local disease recurrence.

Tumor Biology

Multilobular osteochondrosarcoma (MLO) is a relatively uncommon tumor, with no clear breed or sex predilection.  It generally arises from the skull of dogs (cranium, orbit, zygomatic arch, mandible, and maxilla); and has a characteristic “popcorn” appearance on diagnostic imaging due to its well-circumscribed, lobular, and granular features.

Clinical signs are dependent on the location and extent of the tumor. Patients most often present with a palpable, fixed, firm mass on the skull. They may have pain upon opening the mouth if the tumor involves the mandible and zygomatic arch. Exophthalmos can be seen with infraorbital lesions.

For tumors invading the calvarium, neurologic dysfunction may be present. Surgical excision is the treatment of choice for MLOs if possible.

For non-resectable tumors, palliative radiation and stereotactic radiation have been described although their effectiveness is currently unknown.  Based on the literature, 47-58% of dogs treated with surgery have local tumor recurrence, with a median time to local recurrence of 426-797 days.

Prognostic factors for local recurrence include completeness of surgical margins and histologic tumor grade. 56-58% of dogs develop metastatic disease a median of 426-542 days post-operatively. Metastasis is significantly more likely for incompletely excised tumors and high-grade tumors.  In general, dogs with histologically low-grade tumors that undergo complete surgical excision have a very good long-term prognosis.

About the author

Chloe Wormser, DVM, DACVS

wormser_c-110x110Dr. Chloe Wormser is a Diplomate of the American College of Veterinary Surgeons. She is originally from Chicago and graduated from the University of Pennsylvania School of Veterinary Medicine in 2011. She continued her training at UPenn, completing a rotating internship followed by a residency in small animal surgery.  She moved with her husband and three dogs to Saratoga Springs, New York in 2017.

Dr. Wormser’s surgical interests include orthopedic surgery, microvascular surgery, urinary tract surgery, oncologic surgery, and minimally invasive surgery.  She has authored several peer-reviewed journal articles, with research focused on feline renal transplantation and ureteral disease. In her free time, she loves traveling and spending time outdoors.

Article notes


  • WS Dernell, RC Straw, MJ Cooper, BE Powers, SM LaRue, SJ Withrow. Multilobular osteosarcoma in 39 dogs: 1979-1993. J Am Animal Hosp Assoc1998; 34(1): 11-18.
  • RC Straw, RA LeCouteur, BE Powers, SJ Withrow. Multilobular osteochondrosarcoma of the canine skull: 16 cases (1978-1988). J Am Vet Med Assoc. 1989; 195(12): 1764-1769.
  • ST Kudnig, B Seguin, eds. Veterinary Surgical Oncology. John Wiley & Sons, Ltd. 2012.

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