Background: The potential unrevealed clinicopathological differences between simple bone cysts situated in the calcaneus (calcaneal bone cysts) and those situated in long bones (long bone cysts) were investigated in the present study.
Methods: A total of 41 cysts from 41 patients who underwent operative treatment were evaluated: 16 cysts in the calcaneus, 17 in the humerus, 7 in the femur, and 1 in the tibia. The clinical course, radiological findings, and histological features were retrospectively reviewed.
Results: The mean patient age was 11.5 years (range, 3 to 25 years), and the mean follow-up was 33.0 months (range, 12 to 77 months). The mean patient age was significantly higher in patients with calcaneal bone cysts (13.5 years; long bone cysts, 10.2 years, P < .05). No treatment failure was seen for patients with calcaneal bone cysts, while 7 long bone cysts required reoperation. In H&E-stained specimens of the cyst wall, cholesterol clefts were identified in 10 of the 16 calcaneal bone cysts (62.5%), whereas none were identified in long bone cysts (0%; P < .0001).
Conclusion: Our study elucidates the different clinicopathological features existing between calcaneal bone cysts and long bone cysts. Cholesterol clefting is most likely due to hemorrhaging and the subsequent breakdown of blood in the cyst. The significance of these differences between long bone and calcaneal cysts is still open to conjecture.
Level of evidence: Level III, retrospective comparative series.
Keywords: calcaneal bone cyst; calcaneus; cholesterol cleft; simple bone cyst; solitary bone cyst; unicameral bone cyst.