Pleomorphic Hyalinizing Angiectatic Tumor

Differential Diagnosis

Ancient Schwannoma	Pleomorphic Hyalinizing Angiectatic Tumor
S100 positive	S100 negative
CD34 negative on large cells	CD34 80% positive on large cells
Usually encapsulated	Microscopically infiltrative border
Vessels usually lack fibrin	Fibrin frequent in and around vessels

Both schwannomas and PHAT may show pleomorphic cells with hyalinization and clusters of dilated vessels in a mitotically inactive tumor

MFH	Pleomorphic Hyalinizing Angiectatic Tumor
Mitotic figures present, frequently atypical	Mitotic figures rare
CD34 negative	CD34 80% positive on large cells
Usually deep soft tissue	Usually subcutaneous
Overall high cellularity	Lacks high cellularity overall

Both MFH and PHAT may have increased Factor 13a positive cells

Pleomorphic Lipoma	Pleomorphic Hyalinizing Angiectatic Tumor
No intracytoplasmic hemosiderin	Intracytoplasmic hemosiderin
No aggregates of large vessels	Aggregates of vessels with hyalinized walls and fibrin
Ropy collagen	No ropy collagen
Restricted to back of neck, upper back and shoulders	Various locations

Both are CD34 positive

Hemosiderotic Fibrohistiocytic Lipomatous Lesion has been proposed by Folpe and Weiss to represent early phase PHAT