Diagnosis of Wrist Swelling

The clinical presentation strongly suggests a Ganglion cyst. Key indicators include:

• Location: Swelling on the dorsum of the wrist is a classic site for ganglion cysts.
• Nature: The swelling is described as cystic and nontender, consistent with a ganglion cyst.
• Provocative Sign: The cyst becoming more prominent on plantar flexion is a hallmark sign (sometimes called a positive Watson's test variant), indicating its connection to underlying joint structures or tendon sheaths which are tensed in this position.

Differential Diagnosis Consideration

Other cystic lesions are less likely given the specific features:

• Sebaceous cyst: Typically arises from a sebaceous gland in the skin, often has a punctum (central pore), and is not usually related to deeper joint structures.
• Dermoid cyst: A congenital tumor, less common on the wrist, and may contain skin elements like hair or sebaceous material.
• Epidermoid cyst: Also a skin-derived cyst, often presenting with a punctum, and not typically associated with joint movement provocation like this.

Therefore, the combination of location, cystic nature, and specific provocative sign makes Ganglion cyst the most probable diagnosis.