Patients who undergo Mohs micrographic surgery are often taken aback by the size of the resulting scar, a US study finds.

More than 80% of patients, when asked before their surgery to predict the size, underestimated the length of their resulting scar by about half, according to the report published in JAMA Network Open.

Study co-author Dr Joseph Sobanko, director of dermatologic surgery education at the University of Pennsylvania, Philadelphia, said patients saw the diameter of the lesion and assumed the incision wouldn’t be much bigger than that.

But because the lesions were generally circular, surgeons needed to extend the incision in a triangular shape to allow the skin to lie flat when the edges were closed.