has part has part characteristic of has modifier Abnormality of the thenar eminence Small thenar eminence The reduced soft tissue is typically abductor pollicis brevis and flexor pollicis brevis muscle bulk. Detection of this abnormality entails clinical judgment, especially in mild cases. The bulk of the muscle mass around the base of the thumb is diminished, and there may be a mild concavity over the volar aspect of the first metacarpal. When the deficiency is unilateral, comparison between the two hands will point up the often-subtle change in contour of the thenar muscles. If the degree of involvement is severe, the palm may taper in width proximally. abnormal hypoplastic thenar eminence