Presentation
Left arm pain.
Patient Data
An intramedullary osteolytic bone lesion is seen occupying the proximal humeral metaphysis and diaphysis with mild cortical expansion and rarefaction.
An intramedullary cystic bone lesion involving the upper half of the left humeral shaft distal to the proximal humeral physis with mild expansion of bone cortex. It is measuring 2 x 1.5 x 9 cm in AP, SS and CC dimensions. It shows homogeneous density content with eccentric bone septations. No fractures detected.
The patient has history of a fall at home with pain and inability to move arm three years ago.
Pathological fracture is seen traversing the proximal humeral osteolytic lesion with fallen bone chips inside its cavity (fallen fragment sign).
The patient was managed with cast splint. Callus formation at fracture edges is seen.
Case Discussion
The proximal humerus is the most common location of a unicameral bone cyst (~60%), It is also common in males at this age. Pathological fracture is the most common first presentation, as it is usually asymptomatic.
Fallen fragment sign is the appearance of a displaced fractured bone chip at the dependent part of a cystic bone lesion, reflecting its single cavity nature in the setting of pathological bone fracture and is considered pathognomonic of unicameral bone cyst.
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