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
1. Straw RC,
LeCouteur RA,
Powers BE,
Withrow SJ.
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.
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