Transillumination refers to the use of transmission of light through the body to distinguish between cystic and solid masses. It can therefore provide useful clues for diagnostically challenging hand lesions, because the treatment of solid hand neoplasms1 differs considerably from that of myxoid cysts.2
The penlight3 is usually too weak to serve as a diagnostic aid, even when the room lights are dimmed. An electronic flash unit placed under the affected finger and synchronized with the camera through cable permits the capture of a detailed picture of subcutaneous lesions in broad daylight, even in dark-skinned patients. Transillumination of a straightforward myxoid cyst (Figure, A) allows more light to pass through, resulting in lucent-filling defects (Figure, B). The same pattern (Figure, D and F), obtained for clinically doubtful lesions (Figure, C and E), easily confirms their cystic nature, whereas solid masses (Figure, G [giant cell tumor of tendon sheath]) produce an area of increased opacity (Figure, H). Anatomical considerations limit the usefulness of this technique to suspicious skin lesions on the fingers.