Title: Pelvic Digit

Imaging Findings:
Figures Plain film and CT display an elongated bony process (arrows) abutting the proximal right femur.

Clinical:
Asymptomatic, incidental finding.

Etiology:
Embryologic nonfusion of first coccygeal cartilaginous costal (rib) anlage prior to six weeks (1). Normally these embryologic centers fuse with the first coccygeal body. Other theories suggest origin from the pleuripotentiality of mesenchymal stem cell tissues (2). Digit arises near the bony pelvis, lower ribs, or within the abdominal wall (3), and may or may not pseudoarticulate with the axial skeleton.

References:
1. Reiter A (1944) Die Fruhentwicklung der menschlichen Wirbelsaule, III. Mitteilung. Die Entwicklung der Lumbal-Sacral und Coccygealwirbelsaule. Z Anat Entwicklungsgesch 113:204.
2. Granieri GF, Bacarini L. The pelvic digit: five new examples of an unusual anomaly. Skeletal Radiol (1996) 25: 723-726.
3. Nguyen VD, Matthes JD, Wunderlich CC. The pelvic digit: CT correlation and review of the literature. Comput Med Imaging Graph 1990; 14: 127-131.