Review Article

Unicameral (Simple) Bone Cysts

Authors: Rafath Baig, MD; John L. Eady, MD

Abstract

Since their original description by Virchow, simple bone cysts have been studied repeatedly. Although these defects are not true neoplasms, simple bone cysts may create major structural defects of the humerus, femur, and os calcis. They are commonly discovered incidentally when x-rays are taken for other reasons or on presentation due to a pathologic fracture. Various treatment strategies have been employed, but the only reliable predictor of success of any treatment strategy is the age of the patient; those being older than 10 years of age heal their cysts at a higher rate than those under age 10. The goal of management is the formation of a bone that can withstand the stresses of use by the patient without evidence of continued bone destruction as determined by serial radiographic follow-up. The goal is not a normal-appearing x-ray, but a functionally stable bone.


Key Points


* Ninety-four percent of unicameral bone cysts occur in the proximal humerus and proximal femur, with the proximal humerus being affected two to three times more frequently than the proximal femur.


* The remaining 6% occur in other bones including the calcaneus (2%), ilium (2%), talus, tibia, metatarsals, fibula, ischium, pubic rami, sacrum, vertebral bodies, forearm, and craniofacial bones.


* The typical radiographic appearance is that of a lesion concentrically located in the medullary cavity of the metaphysis of a long bone with expansion in all directions, creating an expanded and thinned but unpenetrated cortex.


* The “fallen leaf” sign on plain films is virtually pathognomonic of a multiloculated bone cyst.


* Aspiration of both unicameral and aneurysmal bone cysts in children below age 10 will frequently produce blood, even with gentle aspiration pressure on the syringe.


* Rarely, simple bone cysts have been noted to cross the physis in very young patients, but this finding has been observed in older patients, as documented by MRI and injection techniques.


* The only reliable predictor of treatment success is the age of the patient; those older than 10 heal at a higher rate (90%) than those under 10 years of age (60%), no matter what treatment regimen is utilized.


* The primary goal of management is a healed bone that can withstand predictable functional stresses of activity by the patient.

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