Also known as: immature nerve sheath myxoma
- Benign tumor of controversial histogenesis
- Most often seen in young adults, with a female predominance
- May affect any area of the body, but most common on the head and neck
- Firm pink to red-brown papule or nodule
- May recur if incompletely excised
- Ill-defined lesion filling the dermis and sometimes extending into the subcutis
- Fascicular, nodular, nested or plexiform pattern
- Composed of epithelioid to spindled cells with abundant eosinophilic cytoplasm and ovoid nuclei with prominent nucleoli
- Numerous mitoses can sometimes be seen.
- Foci of significant atypia are sometimes present.
- In contrast to classic neurothekeoma, myxoid change is not a prominent feature.
- Stromal changes can include chronic inflammation, fibrosis and hyalinization.
- The epidermis can on occasion show melanocytic hyperplasia.
- Immunohistochemistry of is of limited utility. The tumor is negative or only weakly positive for S-100, Leu-7 (CD57), type IV collagen and EMA. Some cases are positive for NSE, MSA or CD34. The only universally positive immunohistochemical stain is vimentin.