Giant ameloblastoma: Report of an extreme case and a description of its treatment.

From the Division of Otolaryngology, Department of Surgery, George Washington University School of Medicine and Health Sciences, Washington, D.C.

Reprint requests: C. Anthony Hughes, MD, NAVAVSCOLSCOM, 181 Chambers Ave., Suite C, Pensacola, FL 32508. Phone [phone]; e-mail: [e-mail]

Abstract

Ameloblastoma is an odontogenic tumor that usually occurs in the mandible. It is an aggressive but benign tumor of epithelial origin that is rarely metastatic. We report the case of a 53-year-old woman who had a massive ameloblastoma of the mandible. The tumor measured 15.2 x 11.4 x 12.0 cm. The patient had oral bleeding that required a transfusion. The workup included three-dimensional imaging, arteriography, and embolization to control bleeding. Surgical management entailed the resection of the entire left mandible and right symphysis, followed by reconstruction with a free fibular flap. To our knowledge, this is the largest reported ameloblastoma managed with three-dimensional imaging, radical resection, and free-flap reconstruction. This article also reviews aspects of the differential diagnosis, pathology, and management of jaw tumors.

Introduction

An ameloblastoma is an odontogenic tumor of epithelial origin that can be locally aggressive. [1] A relatively uncommon tumor (reported incidence: 3 per 10 million), it has a predilection for the mandible, and it accounts for approximately 1% of all tumors and cysts that occur in the jaw. [2] Ameloblastoma can develop at any age, but its peak incidence occurs during the third and fourth decades, and its incidence is divided equally between the sexes. [3] In developed countries, ameloblastoma is usually treated early, so these tumors do not normally reach sufficient size to qualify as a giant ameloblastoma. Our case is reported because of its rarity, size, and management, which involved three-dimensional imaging, radical resection, and free-flap reconstruction.

History. Guzack in 1826 and Broca in 1868 recorded similar lesions in the literature, but it was not until 1879 that Fallson provided a thorough description of an ameloblastoma. The lesion was further described in 1885 by Malassez, who called it an adamantinoma. The term ameloblastoma was coined by Ivy and Churchill in 1934 The term giant ameloblastoma should be reserved for lesions that are truly large and that cause gross asymmetry and regional dysfunction.

Origin and histology. Ameloblastoma can originate in the dental lamina (or its derivatives, such as epithelial rests), in the epithelial lining of odontogenic cysts, in basal cells of the surface epithelium, and in epithelium of the enamel organ. [6] The histologic picture of ameloblastoma involves the palisading columnar ameloblastic cells at the periphery, with nuclei polarized away from the basal membrane (reverse polarization). Loose, stellate, reticulum-like cells inhabit epithelial islands, which can be found within a fibrous stroma (follicular pattern). Islands of mature fibrous stroma can also be found intermingled with strands of epithelium (plexiform pattern). In both patterns, the outermost cells resemble those of the ameloblastic layer and the inner enamel epithelium. Histologic variations within the epithelial islands give rise to histologic subclasses (e.g., cystic, acanthomatous, granular cell, basal cell, and hemangiomatous). [7]

Case report

A thin, frail, 53-year-old woman was admitted to the hospital with a 6-year history of a growing mass in her left jaw (figure 1). She had experienced hemorrhaging in the oral cavity, and a foul-smelling drainage exuded from cutaneous fistulae in the left submental area. She had a cantaloupe-sized mass of the left mandible, a necrotic cavity in the left floor of the mouth, and two draining fistulae in the left submental area. The woman had been evaluated 6 years earlier for an enlarging jaw mass, and a biopsy at that time revealed an ameloblastoma. She had been offered surgical excision then, but she refused.

In the months leading up to this latest hospitalization, the woman had been unable to maintain adequate nutrition because of the size of the mass. She sought medical care only after the bleeding from her oral cavity had become uncontrollable. On admission, the patient was anemic (hematocrit: 22), hypophosphatemic (1.6), and hypoproteinemic (protein: 3.4; albumin: 1.6). She required a 4-unit transfusion of packed red blood cells to stabilize her hematocrit at a level of 28. Three-dimensional computed tomography (CT) showed that the large mass involved the entire left mandible and obliterated the temporomandibular joint (figure 2). Multiple central areas of hypodensity were consistent with multicystic ameloblastoma. Arteriography was performed to determine the source of the tumor's vascular supply, and the mass was embolized with fibrin glue to control bleeding.

Several days after admission, the patient was taken to the operating room for a complete resection of the mass and a percutaneous gastrostomy. After nasotracheal intubation, the mass was resected by dividing the mandible at the symphysis, freeing the tumor from the floor of the mouth, and dissecting to the area of the previously existing temporomandibular joint. The most difficult aspects of dissection were the freeing of the mass from the area of the glenoid fossa and the sparing of blood vessels at the base of the skull. Ivy loops were placed on the right to achieve dental occlusion, and the skin and mucosa were then reapproximated loosely. Histologic examination identified the ameloblastoma as being of the plexiform type (figure 3). The tumor measured 15.2 x 11.4 x 12.0 cm and weighed 1.28 kg (figure 4).

The second-stage reconstruction with a free fibula flap was performed 68 days after the initial procedure. The interval between the two procedures provided sufficient time for the patient to gain weight and for her medical condition to improve. Pathologic examination conducted during the first-stage operation revealed a positive margin at the mandibular symphysis, and a further 1.5 cm of the right parasymphyseal bone was resected during the free-flap reconstruction. The patient recovered from both procedures without complications. Subsequent followup revealed that the patient was doing well. Six weeks after the second procedure, she had gained weight and was pleased with the result. A third procedure, a scar revision, was performed without complication at 6 months, with a good result (figure 5). In the 2 years that followed the scar revision, the patient continued to do well, was very pleased with the final result, and had no evidence of recurrence.

Discussion

Although giant ameloblastoma is rare in developed societies, it can occur in patients who delay treatment because they fear surgery, as was the case in this patient. Even though she had been incapacitated by her disease, it still required many discussions to convince her of the need for resection. She had not been able to maintain her nutritional status, and she had experienced significant weight loss, hypoproteinemia, and anemia.

Five previous cases of ameloblastoma with secondary hypoproteinemia have been reported. [8-11] It is hypothesized that protein leakage occurs in the cyst that eventually causes the condition. [11] Our patient was also malnourished because the size of her lesion impaired her ability to eat; this could account for the finding of hypoproteinemia. Her anemia was most likely caused by chronic bleeding. Her hypophosphatemia with relative hypercalcemia can be explained by chronic osteolysis and resorption of bone. These abnormalities resolved with improved nutrition after the mass was resected.

In patients with jaw masses of this extreme size and with characteristic findings on imaging studies, the diagnosis is relatively clear. However, jaw masses in general originate in odontogenic cysts or tumors, or from nonodontogenic causes. Lesions of this size can occur in odontogenic keratocysts, in ameloblastic fibromas, and in Pingborg's tumors, which originate from odontogenic sources. Fibrous dysplasia, or histiocytosis, which originates from nonodontogenic sources, can also produce a large tumor in the jaw.

Although standard CT imaging is the norm, a three-dimensional reconstruction benefits surgical planning and reconstruction by accurately defining the extent of disease. Arteriography is also recommended to delineate the lesion's vascular supply so that embolization can be performed when necessary.

The mainstay of therapy for giant ameloblastoma is surgical resection. Enucleation is inadequate for large lesions because there is a high rate of recurrence. Bony surgical margins of 1 to 2 cm are recommended. [12,13] Historically, these tumors have been thought to be radiation-resistant, although more recent reports suggest some success with megavoltage irradiation [14] and with combined chemotherapy and radiation. [15,16] Caution should be exercised, however, because histologic transformation can occur. A history of radiation exposure has been reported in patients who were diagnosed with ameloblastic carcinomas. Lifelong followup is mandatory in these patients, regardless of the treatment option. Recurrence rates are high, especially in patients with inadequately resected tumors.

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