Incidence and morphologic characteristics of benign calcaneal cystic lesions on MRI

Background: Since we have frequently noted osseous cyst-like lesions within the calcaneus on MRI studies, we sought to systematically evaluate this finding to determine the incidence and morphologic characteristics on MRI. Methods: Three observers blinded to age evaluated 198 MRIs of the ankle (74 males, 124 females; mean age 47 years, range 13 to 99 years), recording the presence and size of calcaneal cyst-like foci. Statistical analysis was performed to determine if there was an association with age. Additionally, MRI of 12 ankles precontrast and postcontrast were reviewed for the presence of blood vessels in the calcaneus corresponding to the location of the cyst-like lesions and 24 ankle MR arthrograms were reviewed to evaluate communication of the cyst with the adjacent joint. Results: Of the 198 ankle MRI examinations, 81 (40%) had hyperintense foci, all within the mid-calcaneal body. The size ranged from 0.01 cm(2) to 2.47 cm(2), with a mean size of 0.36 cm(2) (+/- 0.45 cm(2)). Thirty-seven (46%) were linear or elongated, whereas 44 (54%) were ovoid or round. Seven of the 81 foci (8.6% or 3.5% of the total population) were 1 cm(2) or larger. There was no significant association of patient age and presence (p = 0.49) or size (p = 0.48) of the focus. Location of the cyst-like foci, which often are ovoid or linear, corresponds to penetrating microvessels on precontrast and postcontrast MRI. One MR arthrogram showed communication of a cyst-like focus and the subtalar joint. Conclusions: Calcaneal lesions are relatively common incidental findings on MRI. These lesions appear to represent intraosseous ganglion cysts that arise from the anterior margin of the posterior facet of the subtalar joint in the anatomical neighborhood where vessels penetrate the superior calcaneal cortex. The lesions can vary is size; however, there is no correlation between patient age and lesion size and no significant association between age and presence of these foci.