- Harmatomatous proliferations of nerve sheath components
- Divided into spontaneous (palisaded encapsulated neuroma) and traumatic types
Palisaded encapsulated neuroma:
- Most occur on the face.
- Small skin-colored, dome-shaped papules
- Well-circumscribed dermal nodule
- Tight fascicles of spindle cells with ovoid or wavy nuclei
- The fascicles are often separated by clear clefts.
- Partially enclosed by a thin capsule composed of perineurium
- Significant palisading is usually not present, despite the name.
- Multiple tumors with an identical appearance, with the exception of encapsulation, can be seen in multiple mucosal neuroma syndrome or MEN 2A.
- S-100 positive
- The perineurial capsule is positive for EMA.
- Occurs following damage to a peripheral nerve, with Wallerian degeneration and subsequent imperfect regeneration, resulting in an irregular, disorganized growth at the proximal end of the transected nerve.
- Firm, skin-colored papule or nodule at a site of previous trauma
- Older lesions may be painful.
- Supernumerary digits represent a form of traumatic neuroma occurring after in utero amputation of an extra digit.
- Well-circumscribed dermal or subcutaneous nodule
- Haphazard tangle of nerve fascicles varying in size and shape, separated by collagen and variable chronic inflammation
- The nerve fascicles closely recapitulate normal nerve tissue, with normal proportions of the various cell types.
- The lesion is partially or completely enclosed in a fibrous sheath.
- Mucinous changes may be seen in early lesions.
- S-100 positive
- The perineurial cells within the fascicles are positive for EMA.