Types of mastocytosis coded to 9740/1 are non-reportable: cutaneous mastocytosis (CM) where the mast cell infiltration is confined to the skin; and extracutaneous mastocytoma , an extremely rare unifocal low-grade mast cell tumor with no skin lesions.
Urticaria pigmentosa/maculopapular cutaneous mastocytosis is the most frequent form of CM. In children the lesions of UP tend to be larger and papular. Histopathology typically reveals aggregates of spindle-shaped mast cells filling the papillary dermis and extending as sheets and aggregates into the reticular dermis, often in perivascular and periadnexal positions. A subvariant, usually occurring in young children, presents as non-pigmented, plaque-forming lesions. In adults the lesions are disseminated and tend to be red or brown and macular or maculopapular.
Diffuse cutaneous mastocytosis occurs almost exclusively in childhood. The skin is diffusely thickened and may have an orange peel appearance. There are no individual lesions. Atypical cells are not present, which can help distinguish this disease from a mast cell sarcoma (9740/3) occurring in the skin.
Mastocytoma of skin occurs as a single lesion, almost exclusively in infants. These mast cell infiltrates may extend into the subcutaneous tissues.
Extracutaneous mastocytomas has been reported in the lung. This isolated mast cell tumor has a non-destructive growth pattern.