\s=b\ Aneurysmal bone cyst is an uncommon benign lesion that rarely presents in the craniofacial region. No prior reports of this entity involving the mandible could be found in the otolaryngologic literature, and it has been reported only infrequently in the maxilla. Two previously unreported cases originating in the mandible are presented with a review of the literature, pathology, and diagnosis of this lesion.Treatment of this lesion consists of complete surgical removal and immediate bone grafting for reconstruction. (Arch Otolaryngol Head Neck Surg. 1989;115:865-870) Although 50% of aneurysmal bone cysts (ABCs) are found in the long bones of the body and another 20% are found in the vertebral column, its occurrence in the craniofacial area is rare, with involvement of the man¬ dible being less common than the max¬ illa. Because of its infrequent appear¬ ance, ABCs may be confused with neoplastic lesions requiring vastly dif¬ fering treatment. To avoid incorrect diagnosis, the pathologist should be familiar with the clinical presentation. Even after an adequate biopsy is per¬ formed, the diagnosis may be in ques¬ tion, with the exact diagnosis not de¬ termined until the entire tumor is ex¬ cised. In the past, management has consisted of curettage, cryotherapy, and local resection. Two case studies are presented as well as a review of the literature, diagnosis, pathology, and treatment of this interesting lesion. The etiology and pathogenesis of ABCs remain unclear, but several theories are reviewed. REPORT OF CASESCase 1.-A 14-year-old white adolescent was originally seen at Geisinger Medical Center, Danville, Pa, Oct 8, 1986, on refer¬ ral from his local physician. He had been well until six weeks before his initial exam¬ ination, when he developed a small lump in his left cheek. At that time, it was nontender and not associated with an upper respiratory tract infection, fever, chills, eating, or history of antecedent trauma. He was taken to a local emergency room and treated with amoxicillin for a suspected "ear infection." The patient had no im¬ provement on this medical regimen and was seen again in an outside emergency room, where a chest roentgenogram and complete blood cell count were obtained and were both found to be normal. The patient was admitted to his local hospital, and treat¬ ment was begun with intravenous cefazolin sodium. While in the hospital, he was ex¬ amined by a local otolaryngologist who re¬ ferred the patient to our institution. Over the four weeks since the patient had first noticed the mass, it had slowly increased in size, become tender, and the patient now complained of trismus.On physical examination, a 10 X 8-cm firm, tender mass on the left side of the face protruded 4 to 5 cm, producing obvious fa¬ cial asymmetry. The mass was nonmobile, with no evidence of fluctuation. Examina¬ tion of the oral cavity revealed the patient could only open his mouth 2 cm. Cranial nerves V and VII were intact bilaterally. The rest of the physical examination re¬ sults were unremarkable.A co...