Aneurysmal bone cyst is a solitary vascular abnormality and an expanding osteolytic lesion occurring within the marrow of cancellous long bones. It is usually located at the metaphyseal end of long bones. Fine needle aspiration cytology (FNAC) of aneurysmal bone cyst shows only RBC's and is inconclusive. Cystic lesions such as aneurysmal bone cyst, unicameral bone cyst, and some telengiectatic osteosarcoma yield specimens containing predominantly blood or fluid with little diagnostic cellular content. Ref: Cytopathology of Bone and Soft Tissue Tumors By Lester J. Layfield , page 8; Diagnostic Imaging of Musculoskeletal Diseases: A Systematic Approach By Akbar Bonakdarpour, Pages 283-5; Bailey and Love's Sho Practice of Surgery, 24th Edition, Page 434; Textbook of Disorders and Injuries of the Musculoskeletal System By Robe Bruce Salter, Section II, Page 398.