Striated muscle: a normal component of the dermis and subcutis in many areas of the face.

Abstract

Striated muscle is typically not mentioned in histology chapters of most dermatology and dermatopathology books. In others, authors only speak of its presence in the dermis or subcutis but do not provide any details about its quantity, distribution, or orientation. In the course of an investigation concerning regional histologic variations of the skin, the presence of striated muscle fibers (StrMFs) has been a noteworthy feature of many areas of the face. Striated muscle fibers are a normal constituent of the dermis of the eyebrow (few and deep fibers); eyelid and nose (excluding the nasal tip) (numerous and deep fibers); and lips and chin (numerous, vertical, and more superficial fibers). They are also found in the subcutis of all these areas with some differences in density and distribution among them. Striated muscle fibers form a compact layer beneath the subcutaneous fat on the forehead and cheek, but because of their deep location, they are rarely included in cutaneous biopsy specimens of the latter area. Mainly based on the presence of StrMFs in the dermis, an algorithm to accurately determine the location of biopsy specimens from the face has been elaborated. With the aid of other features such as the type of hair follicles and the presence and degree of solar elastosis, the sex and approximate age of the patient can be established in many cases. Some practical and scientific consequences of these findings are discussed.