2023 Friday Quiz 9 Answer | Figure 1

CincyKidsRad

2023 Friday Quiz 9 Answer

Sagittal T2 (image 1) and T1 (image 2) show a unicameral bone cyst (arrow) of the mid right calcaneus. On the T2 weighted image, a fluid level is present confirming the diagnosis of a cyst. The two most common calcaneal lesions are unicameral bone cyst and intraosseous lipoma. Both lesions are benign and arise under the calcaneal sulcus. They have a similar appearance creating a rounded triangular structure pointing upward. Central calcifications are present in up to three quarters of lipomas. However, they can be difficult to distinguish from coarsened trabecula. MRI can help to distinguish the 2 entities, if needed.

Similar cases

Lateral x-ray of the ankle shows a well-defined lucent lesion (arrow) in the calcaneus. The differential diagnosis for a lesion in this location is a unicameral bone cyst versus an intraosseous lipoma. These lesions can be hard to differentiate on x-ray. Occasionally an intraosseous lipoma can have internal calcification. Both diagnoses are benign. #MSKMonday

Axial T2-weighted (Image 1), sagittal T2-weighted (Image 2), and sagittal T1 post-contrast (Image 3) MRI demonstrate an expansile mass with multiple internal septations. The compartments exhibit fluid-fluid levels (arrow), indicative of an aneurysmal bone cyst. Such cysts are benign lesions and are frequently found in the femur and tibia. They appear on radiographs as expansile lucent lesions with potential bony septations. MRI typically reveals a heterogeneous appearance with multiple fluid-fluid levels. Treatment involves curettage and bone grafting.

Sagittal T2 weighted MRI of the talus shows the lesion with multiple fluid-fluid levels. When multiple fluid-fluid levels are present, the typical differential diagnosis is aneurysmal bone cyst or telangiectatic osteosarcoma. In this case, the radiographic appearance is not aggressive and the cysts are regular in shape consistent with an aneurysmal bone cyst. Aneurysmal bone cysts may be primary or secondary lesions. When a secondary lesion, they can be associated with giant cell tumor, osteosarcoma, and chondroblastoma among other lesions. #FridayQuizDay

A lateral radiograph of the hindfoot shows a lucent lesion (arrow) within the anterior aspect of the calcaneus with a central calcification typical of an intraosseous lipoma. The calcaneus is the most common site for an intraosseous lipoma. A unicameral bone cyst is another lesion that can affect the calcaneus. It is typically not possible to distinguish an intraosseous lipoma from a unicameral bone cyst on imaging alone, but the presence of central calcification makes the diagnosis of intraosseous lipoma more likely.