A symptomatic pelvic digit with surgical and pathological correlation

Abstract

Pelvic digits (also known as pelvic fingers or pelvic ribs) are rare supernumerary benign bony lesions. Most of them are asymptomatic but, when symptomatic, they can pose a diagnostic challenge. We hereby present a case of a pelvic digit responsible for an organic erectile dysfunction and a disabling pain in the sitting position. Pelvic radiographs showed a 2-cm ossified cannulated structure emerging from the right ischiopubic ramus, extending down into the right perineal soft tissues. MRI revealed a well-defined cortico-medullary digit with typical bone signal, developing near the hypertrophied root of the right corpus cavernosum and the insertion of the right adductor magnus muscle. The CT scan confirmed a pelvic digit with a pseudarthrotic single joint on the ischium. After a thorough 2-step surgical resection, pathologists confirmed the diagnosis. This particular radiologic challenge was to differentiate a pelvic digit from osteochondroma, avulsion-fracture sequelae, ligamentous calcification and myositis ossificans.

Keywords: Erectile dysfunction; Exostosis; Pelvic digit; Pudendal neuralgia.

Fig. 1

Pelvic radiography (frontal view). A mature pelvic digit, corticated (black arrow) extending from the right ischium. The proximal joint (white arrow) represents a pseudoarthrotic articulation with the ischiopubic ramus.

Fig. 2

Pelvic MRI (1.5 Tesla). (A) and (B) Coronal T2 Dixon and T1-weighted images showing a pelvic digit with high T1 and low T2 signal intensity, consistent with cortico-medullary bone components (white arrow), and a proximal pseudoarthrotic joint with the ischiopubic branch (white arrowhead). (C) Axial STIR image demonstrating the extension of the digit towards the hypertrophied insertion of the right corpus cavernosum (white arrow). (D) Axial T1-weighted image showing direct contact with the insertion of the right adductor magnus (AM) muscle (white arrow).

Fig. 3

Pelvic CT scan. The pelvic digit extends anteriorly and demonstrates a pseudoarthrotic articulation with the right ischiopubic branch (white arrow). The 3D reconstruction (white arrowhead) highlights its anteroinferior orientation. Note the soft tissue infiltration around the distal end of the digit, particularly in the subcutaneous fat, likely due to chronic mechanical irritation in the sitting position (white underlined arrow).

Fig. 4

Pelvic radiographs (frontal view) before (A) and after (B) partial surgical resection of the pelvic digit. Complete resection was performed 9 months later (C).