M 53, right 3rd finger

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Diagnosis:
Digital mucous cyst, ganglion type
Comment:

Digital mucous cyst: Two types
1. Myxomatous type:
Focal papular mucinosis (Digital myxoma), near the proximal nail fold.
Area of pale blue mucinous material in dermis with cyst formation without any lining.
Mucin is hyaluronic acid and it stains with colloidal iron or alcian blue stain.
Overlying epidermis is thin or ulcerated.

2. Ganglion type:
Located near the distal interphalangeal joint on the dorsum of finger, representing a ganglion cyst.
Cyst is lined by flattened synovial epithelial cells and contains  hyaluronic acid-rich mucinous material.