Pseudotumor of the supraclavicular fossa.

Minor musculoskeletal variants of the upper thoracic spine or of the ribs can cause effacement of the supraclavicular fossa, simulating a mass ("pseudotumor"). These variants may occur singly or in combination, and include unilateral prominence or asymmetry of the first rib, unilateral prominence or asymmetry of a cervical rib, and mild upper thoracic scoliosis causing prominence of the first rib on one side. The detection of variants by physical examination or more easily by review of the chest x-ray film may in selected instances obviate the need for costly diagnostic procedures and unnecessary biopsies. We call attention to this condition and describe our experience with four patients.