SPECT/CT imaging features of cystic degeneration of the talus and their relation to pathological findings.

BACKGROUND

Osteochondral lesions of the talus (OLTs) are a common orthopedic condition. The image presentation is very similar to that of ischemic necrosis of the talus complicated by a talar neck fracture, but the two are very different lesions. When abnormalities in bone density (or signal) of the talar body (apex of the fornix) with concomitant bone defects and cystic changes are found on X-ray, computed tomography (CT), or magnetic resonance imaging, it is important to accurately determine the nature of the lesion and make a correct diagnosis for the treatment and prognosis of the patient. The purpose of this study was to explore the imaging features of three-phase single-photon emission computed tomography (SPECT)/CT images of cystic lesions of the talus.

METHODS

A total of 189 patients with chronic pain in the ankle joint suspected to be caused by cystic degeneration of the talus were enrolled. All patients underwent 99mTc-methyl diphosphonate (99mTc-MDP) three-phase SPECT/CT bone imaging and delayed scans in our hospital. The location, range of involvement, classification, CT value, and radioactivity uptake of the sclerotic areas of cystic lesions on the talus, and the continuity of the articular surface, were recorded. All recorded parameters were analyzed in comparison with pathological results.

RESULTS

Eighty-three percent (157/189) of the talar cysts were located on the medial fornix, largely involving the anterior middle part (43.27%), with larger cysts involving the posterior part (9.6%). Sixty-three percent (119/189) of the patients had type I lesions and 37% (70/189) had type II lesions. The articular surface of the medial dome of the talus was intact in all patients, but the subchondral bony articular surface was rough in 88% (166/189) of patients. The coincidence rate for the location, type, and range of involvement of cystic lesions with the pathological results was 87.83% (166/189). The mean CT value of the cystic lesions was 45 ± 15 HU (30-60 HU). The percentages of pathological chondrogenesis in high CT value ≥ 50 HU (19/70) and low CT value < 50 HU (51/70) groups were 89.47% (17/19) and 29.14% (15/51) (χ = 20.12, p < 0.001), respectively. The target/background ratio (T/B ratio) of the radioactivity-uptake area of the talus vault was 2.0 ± 0.5 (1.5-2.5). The percentages of pathological new trabecular bone in those with a T/B ratio ≥ 2.0 (157/189) and T/B ratio < 2.0 (32/189) were 82.80% (130/157) and 25.00% (8/32; χ = 45.08, p < 0.001), respectively.

CONCLUSIONS

Three-phase bone imaging could identify damage of the talus caused by cystic degeneration, while delayed SPECT/CT images showed advantages for displaying bone microstructure, blood supplement, and bone metabolism when examining the location, range of involvement, classification, and repair of cystic lesions of the talus.