Isolated Malignant Peripheral Nerve Sheath Tumor of the Scalp

Significance Statement

Malignant peripheral nerve sheath tumor (MPNST) is an aggressive, locally invasive, spindle cell tumor of nerve origin with an incidence of 1/100000/year. ¹ We report a patient with an isolated cutaneous MPNST of the occipital region mimicking a benign process and review the current literature in terms of diagnostic approach and survival.

Case Presentation

A 53-year-old man presented with a 2-year history of a painless swelling on the right occipital region posterior to the mastoid process. The relatively soft and mobile, subcutaneous lump had an apparent size of 3 × 3 cm and started to grow slowly over the past few months. There were no paresthesias or redness of the overlying skin or any other superficial lesions. Medical history was unremarkable. The lesion was designated as a “lipoma” and excised under local anesthesia. A sausage-like, encapsulated, 2.5 × 2 × 1 cm, tumor which emerged from the underlying musculature was completely removed. Histology revealed exclusively dense fascicles of spindle cells. The tumor was positive to S-100 protein, vimentin, neuron-specific enolase, and CD56 and showed a mitotic activity of 4/10 HRF. The Ki 67 index was positive in less than 5% (Figure 1). A grade I MPNST was diagnosed and subsequent work up with computed tomography and magnetic resonance imaging of the brain, lungs and abdomen, and bone scintigraphy failed to reveal any metastasis or additional tumors suggestive of NF 1.

Figure 1.

Representative histological section of the tumor showing exclusively dense fascicles of spindle cells (hematoxylin–eosin, ×400).

An extended resection was undertaken due to the aggressive nature of the tumor and the approximation of neoplastic cells to one of the peripheral margins. An island of tissue comprising the scar, the surrounding skin up to 2 cm, the muscle and the periosteum, was removed. Two rotational flaps from the scalp and neck closed the defect (Figures 2 and 3).

Figure 2.

A scar after the first MPNST resection is noted in the right occipital region. A 2-cm wide area including skin, subcutaneous tissue, muscle, and skull periosteum is resected. The defect is closed with a superior and an inferior rotational flap. MPNST indicates malignant peripheral nerve sheath tumor.

Figure 3.

The 1-year postoperative result. The scars are hidden within the scalp and postauricular crease. The hairline has not been distorted improving the final aesthetic result.

Based on the negative histology for residual tumor, the small tumor volume, and the lack of metastasis, no radiotherapy or chemotherapy was instituted. The patient is well without any evidence of local recurrence or metastasis at the last follow-up 7 years postoperatively.

Discussion

The mainstay of MPNST treatment is surgery with adjuvant radiotherapy. ² Chemotherapy is reserved for high grade tumors with increased potential for distant metastasis. Superficial lesions, as the one presented here, do not justify systemic treatment unless metastases are identified. Five-year survival of head and neck MPNST may be as low as 20%. ³ Localization in the head and neck, large tumor volume, positive margins, high histological grade, and an increased proliferation index Ki-67 are adverse prognostic factors. Traditionally, patients with NF 1 had a poorer prognosis than patients with sporadic MPNST but survival rates became equal in the last decade. ⁴ Superficial MPNST has a better prognosis with 62% of patients surviving 3.3 years ⁵ owing to the ease of resection and postoperative surveillance.

Conclusion

Malignant peripheral nerve sheath tumor is a very rare and aggressive tumor. It can cause benign lesions on the skin, and therefore, its removal may be delayed. Complete skin removal is possible without functional or aesthetic problems. Regular follow-up is required for relapse.