Perineurioma

Lester D. R. Thompson, MD

Key Facts

Terminology

Benign peripheral nerve sheath tumor, specifically of perineurial cell derivation that surrounds endoneurial connective tissue space of nerve fibers

Etiology/Pathogenesis

May be related to Schwann cells, fibroblasts, or arachnoid cap cells

Clinical Issues

Women affected slightly more often than men
Presents with solitary, painless mass in superficial subcutaneous soft tissue

Macroscopic Features

Usually discrete but without easily detected capsule

Microscopic Pathology

Superficial subcutaneous or dermal site, well circumscribed
Spindled tumor cells organized in many patterns (fascicles, storiform, pinwheel, whorled, lamellar)
Bipolar, bland, plump spindled cells with pale, eosinophilic cytoplasm
Background stroma is collagenous, myxoid or a mixture, without vascular hyalinization

Ancillary Tests

Variably positive with perineurial markers (EMA, claudin-1, GLUT1, CD34) and collagen IV

Top Differential Diagnoses

Neurofibroma, schwannoma, solitary fibrous tumor, meningioma

An intact surface epithelium is noted overlying a proliferation of spindled cells arranged in a vaguely storiform pattern with focal small whorls. Collections of inflammatory cells are present

There is a haphazard spindle cell proliferation showing a syncytial appearance. The cells show slightly spindled nuclei with cytoplasmic processes. The background stroma is slightly loose to myxoid.

TERMINOLOGY

Abbreviations

Soft tissue perineurioma (STP)

Synonyms

Storiform perineurial fibroma
Perineurial cell tumor

Definitions

Benign peripheral nerve sheath tumor, specifically of perineurial cell derivation that surrounds endoneurial connective tissue space of nerve fibers
- Tumors are traditionally separated into intraneural, sclerosing, and soft tissue perineurioma
- Perineurial cells can be seen in other tumors, such as neurofibroma and schwannoma

ETIOLOGY/PATHOGENESIS

Pathogenesis

May be related to Schwann cells, fibroblasts, or arachnoid cap cells

CLINICAL ISSUES

Epidemiology

Incidence
- Exceedingly rare
- Represents < 0.5% of peripheral nerve sheath tumors
Age
- Wide age range: 2-85 years
- Majority: 2nd-5th decades
  - Mean: 45 years
Gender
- Slight female preponderance
  - Female > male (1.1-1.2:1)

Site

Superficial subcutaneous soft tissue
- Most common in soft tissues of lower and upper extremities
- 2nd most common in trunk
- Head and neck sites affected in ˜ 15% of all perineuriomas
Oral cavity is affected ˜ 4% of the time

Presentation

Most patients present with solitary painless mass
May have syndrome/familial association
- Neurofibromatosis type 2 (NF2)
- Nevoid basal cell carcinoma (Gorlin) syndrome
- Interestingly, both have meningioma in common
  - Perineurium may be derived from arachnoid cap cells

Treatment

Surgical approaches
- Excision is treatment of choice
  - Some advocate for wide excision to prevent recurrence

Prognosis

Local recurrence is uncommon (< 5% of cases)
- May develop late
- Only seen if originally incompletely excised
Metastases are not reported
Pleomorphic cells and infiltrative margins do not affect clinical outcome

MACROSCOPIC FEATURES

General Features