Digital myxoid cysts are solitary, skin-colored or translucent, round to oval, fluctuant cysts on the dorsal or lateral aspects of the fingers or toes. Histologically, multiple clefts or loose connective tissues which contain abundant acid mucopoly- saccarides are seen in the dermis without epithelial lining. There are two types of digital myxoid cysts: myxomatous and ganglion. In the ganglion type, mucous material derives from the joint fluid of the interphalangeal joint. The origin of the gelatinous material from joint fluid is supported by observation of communication between cyst and joint by means of methylene blue injection or MRI imaging. In the myxomatous type, cysts occur independently of the joint as a result of proliferation of fibroblasts overproducing hyaluronic acid. This process may be analogous to local accumulation of mucinous materials in cutaneous focal mucinosis. In both types, trauma and chronic pressure has been associated with the cyst formation.
Epidermal inclusion cysts are the most common cutaneous cysts. They can arise anywhere on the skin, but they occur most frequently on the face, scalp, neck and trunk. Most epidermal inclusion cysts develop spontaneously in the follicular regions or result from inflammation around a pilosebaceous follicle. Most spontaneously developing epidermal inclusion cysts arise from the follicular infundi- bulum. Some may be originated from implantation of a fragment of epidermis by trauma, especially in palms, fingers and soles.
Although the etiology of digital myxoid cyst and epidermal inclusion cyst is still under debate, trauma or chronic pressure has been associated with cyst formation in both types of cyst. Therefore it is possible that the primary formation of the epidermal inclusion cyst is a result of the accidental trauma and the patient’s frequent picking may have led the fibroblasts to overproduce hyauronic acid, forming a secondary myxoid cyst. Another possi¬bility is that some kind of injury accompanied by minor inflammation, unnoticed by the patient, may have led to the development of both myxoid cyst and epidermal inclusion cyst. However, we prefer the former possibility, because since the first appearance of the lesion the patient complained of clear and gelatinous materials on squeezing.
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Different types of cutaneous cysts originating from 2 or more components of the pilosebaceous units can arise within the same lesion. There have been some reports of epidermal inclusion cyst combined with other benign tumors such as trichilemmal cyst, apocrine hidrocytoma and pilomatricoma. There has been only one case reported of simultaneous epidermal inclusion cyst and mucocele in the lower labial mucosa. Since both cysts share a common traumatic etiologic, they might develop concurrently at the same site. However, to the best of our knowledge, there has been no previous report of concomitant occurrence of digital myxoid cyst and epidermal inclusion cyst.