Answer:
The Hamilton-Norwood classification is a method of categorizing male-pattern baldness. It was initially described by Hamilton in 1951 and then modified by Norwood in 1975. It is intended to provide useful standards for screening candidates for hair transplant surgery and documenting patterns of baldness which could be compared over time for any given patient or between different patients and be communicable to other clinicians.
The classification is based on the loss of hair anteriorly and/or on the vertex as well as with the position of the hairline in relation to the external auditory meatus. It goes as follows:
Type I: No or very minimal hairline recession along the anterior border in the frontotemporal region.
Type II: The anterior border of the hair in the frontotemporal region has symmetrc triangular areas of recession which extend no further posteriorly than 2 cm anterior to a line drawn in a coronal plane at the level of the external auditory meatus.
Type III: The triangular areas in Type II extend posterior of the coronal plane which is 2 cm anterior to the external auditory meatus. This is the minimal level considered to represent baldness.
Type III Vertex: Most of the hair loss is seen on the vertex. Frontal hair loss may be similar to Types I or II but should not exceed Type III. This type is most commonly seen with advancing age.
Type IV: Hair loss on the vertex associated with frontal loss more severe than Type III, but the frontal and vertex areas are separated by a distinct band of hair.
Type V: Greater hair loss than Type IV with only a sparse band of hair separating the frontal and vertex areas. The hair left on the occipital and parietal areas begins to form the shape of a horseshoe when viewed from above (also true for Types VI and VII).
Type VI: The frontal and vertex areas of hair loss are contiguous with greater lateral and posterior areas of denudation.
Type VII: The most severe form of male pattern baldness. Only a narrow sparse horseshoe-shaped band of hair is left extending from the ears posteriorly to the occiput.
In addition, Types II through V can also be designated with a Type A variant in which the entire anterior hairline border recedes in unison without leaving the midfrontal peninsula of hair and also in which there is no simultaneous denudation of the vertex.
Type IIA: The hairline is anterior to the coronal plane 2 cm anterior to the external auditory meatus.
Type IIIA: The hairline has receded back to a point between the limit of Type IIA and the level of the external auditory meatus.
Type IVA: The hairline has receded beyond the external auditory meatus but has not reached the vertex.
Type VA: The area of denudation includes the vertex. Hair loss more severe than Type VA cannot be distinguished from Types VI or VII.
Incidentally, female pattern hair loss was classified by Ludwig in 1977. He describes three grades centered on the vertex. Grade I has moderate thinning of hair noticeable around the vertex. Grade II has severe thinning but still with hair strands present. Grade III is complete denudation.
Hamilton-Norwood Classification: