Presentation
Chronic pain and tenderness over his left hip. GP requested an X-ray to exclude hip arthritis or impingement.
Patient Data
Left hip was unremarkable. However, there was an osseous growth projecting from the superior pubic ramus and crossing the left obturator foramen.
CT with 3D reconstruction confirmed a bony growth from the anteroinferior aspect of the left superior pubic ramus formed from two component with pseudo-articulation. Cortex- medullary differentiation is preserved on bone window. This lesion is seen indenting the left pectineus muscle which is seen relatively swollen compared with the right side and mild surrounding inflammatory changes. No aggressive features. No previous imaging available.
Case Discussion
The pelvic digit/rib is considered an incidental finding /a rare congenital anomaly. It usually appears as a rib or digit-like bony structure with a clear cortex and medulla and with a pseudo-articulation. Differential diagnosis of such appearance includes myositis ossificans, bone avulsion, heterotopic bone, and osteochondroma.
A more likely explanation seems to be that the pelvic digits/ribs originate in the embryonic mesoderm, the mesodermal cells of the embryo with the ability to form ribs migrate from the primary slit around the cloacal membrane and make their way from the region of the future coccyx, through the walls of the future pelvis to the lower abdominal wall.
The mesenchyme of the "costal process" usually degenerates due to apoptosis. The absence of apoptosis may allow mesenchyme of the "costal process" to differentiate into rib tissue. These bony structures may contact the adjacent developing bones.
So far, a small number of isolated cases and case series of pelvic rib/digit have been registered. Few of them are symptomatic and most of them appear accidentally. Physicians should be aware that this anomaly can be a cause of pain or disability as in our case.
These lesions are not considered "don't touch lesions" anymore and surgical removal is indicated if symptomatic or associated with functional impairment.
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