Skin PNST

+ General Considerations

• Synonyms: neurogenic sarcoma, neurofibrosarcoma, malignant Schwannoma, malignant neurolemmoma, and hemangiopericytoma
• Hemangiopericytoma may not exist as blood vessel pericyte origin has not been demonstrated and they have same histologic features as a peripheral nerve sheath tumor and stain positive with S-100 immunohistochemistry
• Female predisposition for hemangiopericytoma
• Sites: distal extremities are common
• 3 groups of peripheral nerve sheath tumors:
• Peripheral (i.e., nerves away from the brain and spinal cord)
• Nerve root (i.e., nerves immediately adjacent to brain and spinal cord)
• Plexus (i.e., brachial or lumbrosacral)
• Peripheral form is more amenable to treatment than either the plexus or root forms
• Gross appearance: nodular, lobulated, or poorly defined without histologic encapsulation despite appearing encapsulated and discrete clinically
• Primary cutaneous neurofibroma is rare
• Solitary (common) or multiple (tortuous and nodular enlargement of nerve = neurofibromatosis)
• Adherence to deeper tissues and infiltration of underlying fascia, muscle, and skin is common
• Axial peripheral nerve sheath tumors can cause nodular enlargement and compress adjacent nerves causing unilateral lameness, muscle atrophy, paralysis, and pain with spinal cord invasion possible in up to 50% if grade III STS
• Metastatic rate: 10%-20% for grade I and 50% for grade III
• Peripheral nerve sheath tumor site:
• Nerve root: 72% local tumor recurrence rate with a median DFI 7.5 months and MST 12 months
• Plexus: 72% local tumor recurrence rate with a median DFI 1 month and MST 5 month