Author

Stephen J. Birchard DVM, MS, Diplomate ACVS

Monday, November 10, 2014

Large Tumor On The Skull of a Dog: The story of "Rocky" the Norwegian Elkhound

Rocky was a 7 year old male castrated Norwegian Elkhound. Several months previous to presentation he developed a slowly growing firm mass on the dorsal cranium.  The owners reported no other significant health problems. 
Fig. 1: This is Rocky under anesthesia being prepared for surgery.
Note large mass on the dorsum of the skull.
On physical examination the mass was well circumscribed but not movable.(Fig. 1) Neurologic exam revealed mild posterior paresis. In all other respects Rocky was behaving like a normal dog.

Diagnostic Evaluation

Radiographic evaluation found no evidence of metastasis of the mass in the lungs or abdomen.  A complete blood count and serum chemistry profile was within normal limits. MRI of the skull showed a very large ossified mass of the dorsal cranium extending ventrally into the cranial vault.(Fig. 2)
Fig. 2: MRI of Rocky's head. Note large skull mass (arrows) that extends ventrally.
Surgery

Although Rocky’s owners were warned about risks of surgery such as brain injury, hemorrhage, infection, and possible incomplete resection of the mass, they wanted to pursue surgical removal. They also knew that the most likely neoplasms causing the tumor were osteosarcoma or multilobular osteochrondrosarcoma.

Rocky was anesthetized and placed in sternal recumbency. His entire head was prepared for aseptic surgery. (Fig. 3)
Fig. 3: Preoperative view of Rocky just prior to beginning of surgery
A midline approach over the mass was performed. Sharply dissecting soft tissues including the temporalis muscles, and retracting them laterally, easily exposed the mass. (Fig. 4) 
Fig. 4: Surgical exposure of the skull mass after dissection of the soft tissues.
Dorsal is to the top of the photograph.
Careful blunt and sharp dissection at the base of the mass allowed for gradual moblilization, and the mass and the involved cranium then easily lifted off the remainder of the skull and were excised. (Figs. 5,6)
Fig. 5: Most of the skull mass has been reflected off the remainder of the skull and is
being held upside down in my hand.
Fig. 6: The resulting skull defect after complete removal of the mass.
Moderate hemorrhage occurred from remnants of tumor attached to the dura and at the edges of the skull. Hemostasis was achieved with judicious electrocautery and hemostatic sponges. Careful debridement of the remaining gross tumor was attempted but was difficult because of poor exposure due to recurrent hemorrhage, and attachment of the mass to the dura.

The skull defect was filled with an autogenous fat graft that was aseptically harvested from Rocky’s lumbar area. The temporalis muscles were then mobilized by undermining them from the skull and used as the first layer of closure by suturing them together on the midline. The remaining tissue layers were closed routinely.(Fig. 7)
Fig. 7: Closure of the temporalis muscles over the skull defect
Postoperative Care and Follow Up

Rocky made an uneventful recovery from anesthesia. Repeat neurologic examination revealed no change from his preoperative status. Routine supportive care and analgesic therapy was administered.

Rocky was discharged from the hospital several days postoperatively. Histopathology of the mass revealed a multilobular osteochondrosarcoma. Two weeks later he was examined for suture removal and was doing very well, including improvement of his posterior paresis. He was rechecked again several weeks later and was continuing to do well.(Fig. 8)
Fig. 8: Rocky at his recheck examination several weeks postoperatively
The owners declined any adjunctive therapy such as radiation or chemotherapy, for the tumor.  Approximately 9 months postoperatively Rocky’s mass began to re-grow. Several months later the owners elected to have Rocky euthanized. 

Discussion

Multilobular osteochondrosarcoma (MLO) is a well-described tumor of bone and frequently found on the skull in dogs.(1) The tumor is typically slow growing but locally invasive and can be metastatic. Complete resection of a small MLO can have a good prognosis. However, recurrence of tumor commonly occurs after incomplete resection (approximately 50% of cases) as was the case in Rocky. After surgical treatment, disease free interval of 288-1332 days has been found depending on tumor grade. (2)

Options for reconstruction of large defects of the cranium include rigid materials like polymethylmethacrylate, mesh implants, or autogenous soft tissues using the temporalis muscles. (3) An autogenous fat graft to protect the dura combined with temporalis muscle reconstruction was an effective option for Rocky.

An extraordinary aspect of this case is that Rocky had severe compression of his cerebrum by the tumor, yet had only mild neurologic signs. He also made a surprisingly uneventful recovery from surgery and lived about 1 year postoperatively. Of course we would have preferred to achieve a complete resection of the mass but that was not possible without risking serious complications.

Post questions or comments about Rocky either here or on my Facebook page, Dr. Stephen Birchard, Veterinary Continuing Education. Thanks!

References

Multilobular osteochondrosarcoma of the canine skull: 16 cases (1978-1988).
JAAHA 1989, 195(12):1764-1769]

2. Veterinary Society of Surgical Oncology website: http://www.vsso.org/Bone_MLO.html


3. Boston, SE. Craniectomy and orbitectomy in dogs and cats. Can Vet J. May 2010; 51(5): 537–540.