Aneurysmal Bone Cyst of the Clavicle: A Rare Orthopedic Entity.

Introduction: Clavicle neoplasms account for only 1.01% of bone tumors and the possibility of it being a primary aneurysmal bone cyst is incidentally low. Although rare in incidence, most of the cases reported were treated with en bloc resection either as a primary procedure or during recurrence. The rarity of the disease and the lack of medical literature poses a diagnostic dilemma for the treating orthopedic surgeon, radiologist, and pathologist, that could potentially lead to the lesions being diagnosed at a stage when options to salvage the bone can no longer be considered. In our case, early meticulous work-up, prompt surgical intervention, and strict follow-up enabled us to salvage the bone and, more importantly, preserve the acromioclavicular joint; hence, offering better functional outcome for the patient. Case Report: A 23-year-old female presented with complaints of pain in the left collarbone and restricted movement in the shoulder. Clinically, a bony irregularity was palpable over the left clavicle with associated tenderness. Patient was subjected to various radiological imaging and tissue sampling to aid in the establishment of a pre-operative diagnosis. A diagnostic dilemma arose as the investigations opened up a wide plethora of differentials. Considering the age of the patient and the provisional diagnosis of "giant cell lesion," an attempt was made to salvage the bone and preserve shoulder function. The patient underwent extended curettage, cancellous bone grafting, and augmentation plating. Intraoperative samples were sent for histopathology and the lesion turned out to be one among the least likely on the list of possible differential diagnosis - a primary aneurysmal bone cyst. A meticulous follow-up protocol was devised during which functional outcome was found to be excellent and there was no recurrence at 15 months. Conclusion: Through this case report, we would like to emphasize on the importance of broadening the spectrum of differential diagnosis while investigating tumors at a rare site. This was achieved by devising a meticulous pre-operative radiological and histopathological diagnostic protocol encompassing a spectrum of differential diagnosis. Establishing an early diagnosis gives us an option to opt for surgical interventions for bone salvage and, thus, achieve better functional outcome for the patient.