Malignant peripheral nerve sheath tumor with perineurial differentiation: "malignant perineurioma".

Background: Although benign tumors derived from the nerve sheath perineurial cell have been described from a variety of anatomic sites and are known to be a component of a number of benign neoplasms, malignant nerve sheath tumors of perineurial origin are exceedingly uncommon.

Methods: We report an unusual case of a 70-year-old male who presented with a rapidly growing mass of the left arm, subsequently shown to be a malignant nerve sheath tumor with perineurial differentiation. A brief microscopic differential diagnosis and review of the literature are discussed.

Rhabdomyomatous mesenchymal hamartoma: an unusual dermal entity with a report of two cases and a review of the literature.

Background: Rhabdomyomatous mesenchymal hamartoma (RMH) is a rare congenital lesion of the dermis and soft tissues consisting of a disordered and varied collection of mature adipose tissue, skeletal muscle, adnexal elements and nerve bundles. This entity exists under various names including striated muscle hamartoma, congenital midline hamartoma, and hamartoma of cutaneous adnexa and mesenchyme. Several published cases report the occurrence of RMH within the setting of other uncommon congenital abnormalities.