Diagnosis:

Balloon cell naevus

Comments:

BALLOON CELL NAEVI:

• Dermal or compound naevus of usual type
• Presence of groups or sheets of 'balloon' naevus cells with copious fine vacuolated cytoplasm
• Balloon cells stand out from surrounding population of unremarkable naevus cells
• No 'maturation' of balloon cell component
• A few ascending balloon cells within the epidermis may be present. Because of the ballooning phenomenon, stey stand out more more distinctly in H&E sections than small asecnding naevus cells seen in other naevi. This can be a source of overdiagnosis
• No nuclear atypia
• No, or hardy any, mitotic activity

Reference:

Schrader WA, Helwig EB.  Cancer. 1967; 20: 1502-14.