Unusual malignant perineurioma of soft tissue

Sporadic Malignant Perineurioma: A Rare Diagnosis Among Malignant Peripheral Nerve Sheath Tumors

BACKGROUND

Malignant perineurioma is a rare subset of malignant peripheral nerve sheath tumors (MPNSTs) with ultrastructural and immunohistochemical features of perineurial differentiation, distinguishing it from other MPNSTs, which typically demonstrate Schwannian features. The clinical course and prognosis of this rare tumor is not well defined.

METHODS

The electronic medical records were searched for patients with a diagnosis of MPNST. Patients with a pathologic diagnosis of malignant perineurioma or MPNST with perineurial features were identified and further evaluated.

RESULTS

Five patients with malignant perineurioma, or MPNST with perineurial features, were identified. Four patients (2 male and 2 female) were included with tumors associated with a common digital nerve, small muscular branch to the deltoid, sciatic nerve, and accessory nerve. One patient with the pathology diagnosis meeting inclusion criteria was excluded, as no clinical information was available for this patient.

CONCLUSIONS

Patients in our series presented at varied stages of disease. Clinical courses after diagnosis of malignant perineurioma, where follow-up was available, were largely uncomplicated with regard to recurrence and metastatic disease. Careful follow-up is indicated, and further work is needed to characterize the clinical course of these rare tumors.

Soft tissue perineurioma: clinicopathologic analysis of 81 cases including those with atypical histologic features

Perineuriomas are uncommon benign peripheral nerve sheath tumors that include soft tissue, sclerosing, and intraneural variants. Fewer than 50 soft tissue perineuriomas have been reported to date, and the clinical significance of atypical histologic features is unknown. To characterize these tumors further, 81 soft tissue perineuriomas received between 1994 and 2003 were retrieved from the authors' consult files. Hematoxylin and eosin sections were reexamined, immunohistochemistry was performed, and clinical details were obtained from referring physicians. Forty-three patients were female and 38 male (mean age, 46 years; range, 10-79 years). Tumor size ranged from 0.3 to 20 cm (mean, 4.1 cm) in greatest dimension. Most patients presented with a painless mass. The tumors arose in a wide anatomic distribution: 36 lower limb, 19 upper limb, 15 trunk, 7 head and neck, 3 retroperitoneum, and 1 paratesticular. Forty-two tumors were situated primarily in subcutis, 25 in deep soft tissue, and 9 were limited to the dermis. Nearly all cases were grossly well circumscribed; 12 showed focal microscopically infiltrative margins. Most tumors had a storiform and focally whorled growth pattern; 17 exhibited fascicular areas. Thirty-eight tumors were hypocellular, 15 were markedly hypercellular, and 7 showed alternating zones of hypocellularity and hypercellularity. Stroma was usually collagenous but in 17 tumors was predominantly myxoid, and in 16 was mixed collagenous and myxoid. Mitoses ranged from 0 to 13 per 30 high power fields (mean, 1); 53 tumors had no mitoses. Based on worrisome cytologic or architectural features, 14 cases were classified as atypical perineuriomas: 12 contained scattered pleomorphic cells, 1 showed an abrupt transition from typical morphology to a markedly hypercellular, fascicular area with cytologic atypia, and 1 exhibited diffuse infiltration of skeletal muscle. All tumors were reactive for epithelial membrane antigen; 50 of 78 (64%) expressed CD34, 22 of 76 (29%) claudin-1, 16 of 77 (21%) smooth muscle actin, and 4 of 81 (5%) S-100 protein. All tumors were negative for glial fibrillary acidic protein, neurofilament protein, and desmin. Clinical follow-up was available for 43 patients (mean, 41 months; range, 6-146 months). Among tumors for which the status of surgical margins was known, 52% were widely excised, 31% were marginally excised, and 18% had positive margins. Only two tumors recurred locally (one of which was atypical): one recurred 10 years following primary excision; and one recurred twice, 5 and 9 years following excision. No tumor metastasized. Soft tissue perineuriomas behave in a benign fashion and rarely recur. Atypical histologic features (including scattered pleomorphic cells and infiltrative margins) seem to have no clinical significance and appear to be akin to those seen in ancient schwannoma and atypical (bizarre) neurofibroma.

[Cutaneous perineurioma. Clinical and histological findings and differential diagnosis]

Perineuriomas, composed almost exclusively of EMA (epithelial membrane antigen) positive cells, represent a rare and distinct entity in the spectrum of nerve sheath tumours. At present three subtypes, including intraneural and extraneural perineurioma as well as sclerosing perineurioma, can be distinguished; atypical and malignant perineuriomas are extremely uncommon. We analysed the clinicopathological and immunohistochemcial features of 13 cases of cutaneous perineurioma. The neoplasms arose in adult patients (age range from 18 to 71 years) and were seen on the hand (six cases), the thigh (three cases), the lower leg (two cases), the forearm (one case) and in perinasal location (one case). Morphologically, seven neoplasms showed features of dermatofibroma-like perineurioma, four lesions were consistent with sclerosing perineurioma, one cellular lesion resembled a solitary fibrous tumour, and one case was diagnosed as atypical/malignant cutaneous perineurioma; no local recurrences or tumour progression has been reported so far. The differential diagnosis of various variants of cutaneous perineurioma from other mesenchymal lesions as well as melanocytic and epithelial neoplasms is discussed.