Minor anomalies are herein defined as unusual morphologic features that are of no serious medical or cosmetic consequence to the patient. The value of their recognition is that they may serve as indicators of altered morphogenesis in a general sense or may constitute valuable clues in the diagnosis of a specific pattern of malformation. Those who want a more detailed discussion of this subject or those who desire information on a minor malformation not addressed in this chapter are referred to Jon M. Aase’s Diagnostic Dysmorphology . 2
Regarding the general occurrence of minor anomalies detectable by surface examination (except for dermatoglyphics), Marden and colleagues 9 found that 14% of newborn babies had a single minor anomaly. This was of little concern because the frequency of major defects in this group was not appreciably increased. However, only 0.8% of the babies had two minor defects; in this subgroup, the frequency of a major defect was five times that of the general group. Of special importance were the findings in babies with three or more minor anomalies. This was found in only 0.5% of babies, 10 and 90% of them had one or more major defects as well, as depicted in Fig. 3.1 .
In two additional studies, Mehes and colleagues 10 and Leppig and colleagues 8 demonstrated that 26% and 19.6% of newborn infants with three or more minor anomalies, respectively, had a major malformation, a much lower incidence than that documented in the study by Marden and colleagues and most likely related to differences in study design. Based on these studies, it is concluded that any infant with three or more minor anomalies should be evaluated for a major malformation, many of which are occult.
These minor external anomalies are most common in areas of complex and variable features, such as the face, auricles, hands, and feet. Before ascribing significance to a given minor anomaly in a patient, it is important to note whether it is found in other family members. Almost any minor defect may occasionally be found as a usual feature in a particular family, as noted in Fig. 3.2 .
Figs. 3.3 to 3.8 illustrate certain minor anomalies and allude to their developmental origin and relevance. Many, if not most, minor anomalies represent deformations caused by altered mechanical forces affecting the development of otherwise normal tissue. The reason for the deformation may be purely external uterine constraint. Thus, most minor anomalies of external ear formation at birth are constraint-induced. However, the minor deformational anomaly may be the result of a more primary malformation, and this is the presumed reason for the association between minor anomalies and major malformations.