Osteomyelitis pubis with bilateral muscle abscesses

Clinical History

A 55-year-old male patient, with known type-2 diabetes mellitus, presented with
increasing pubalgia since 2 weeks.
Laboratory examination revealed moderately elevated ESR, CRP and white blood cell count.

Imaging Findings

Radiographs of the pelvis showed widening of the pubic joint and subchondral bone erosions (Fig. 1a and 1b), which were confirmed on subsequent CT of the pelvis (Fig. 2a and 2b). In addition, CT showed soft tissue swelling adjacent to the symphysis in the adductor and rectus abdominis muscles (Fig. 2c and 2d). MRI of the pelvis revealed bone marrow oedema in the iliopubic rami (Fig. 3a and 3b). After administration of gadolinium contrast, bilateral rim-enhancing collections extending from the symphysis pubis were seen along the adductor and rectus abdominis muscles (Fig. 3c, 3d and 3e). The shape of collections along the adductor muscles resembled a butterfly (Fig. 3a and 3b).

Discussion

Osteomyelitis pubis is an infection of the pubic bone and joint, most frequently caused by S. aureus [1]. It’s a rare condition accounting for less than 1% of all cases of osteomyelitis [1].
The exact pathogenesis is unclear, but the infection usually arises from haematogenous dissemination and more rarely by extension of an adjacent infectious focus [2, 3]. This condition has also been called septic arthritis of the symphysis pubis, but osteomyelitis is a more correct term, because the primary site of infection is the pubic bone adjacent to the joint. The infection starts in one pubic bone and later crosses the joint to affect the contralateral pubic bone, analogous to the course of spondylodiscitis.
Potential risk factors are invasive pelvic procedures, pregnancy or delivery, gracilis-adductor tendinopathy and the presence of infectious foci elsewhere in the body which can spread haematogenously [1, 2].

The presenting symptoms and signs are nonspecific [3]. The patient complains of gradually increasing pubic pain, radiating to the groin, perineum, buttock or genital region [2]. Antalgic gait may be present as hip motion aggravates the pain [1, 3]. Inflammatory parameters are usually elevated, but their absence does not exclude the diagnosis [2]. Bacteraemia may be present [2].

Pelvic radiographs are insensitive and are normal in the early stages of the disease [1, 3]. Diastasis of the symphysis and progressive bony destruction will initially appear in one pubic ramus, while the process crosses the joint space at a later stage [3]. Diastasis is suspicious for abscess formation in the joint [3]. CT examination is more sensitive, but its false negative rate remains 10% [2]. MRI is the imaging modality of choice, with a sensitivity that approaches 100% [2]. Typical findings are joint surface irregularities, subchondral bone destruction, bone marrow oedema in the iliopubic rami, soft tissue oedema adjacent to the pubic symphysis and pus in a widened symphysis [1, 2]. After administration of gadolinium contrast, there is enhancement of the infected pubic bone and joint surface. In later stages, a soft tissue abscess will appear as a collection with peripheral enhancement. The abscesses in the adductor muscles may have a characteristic butterfly morphology [1].

Therapy of osteomyelitis pubis consists of long term intravenous administration of antibiotics [1]. In case of failure of conservative treatment, surgery may be indicated [4, 5]. Follow-up imaging is often required [3].

Our patient was successfully treated with antibiotics and follow-up was uneventful. No surgery was required.

Differential Diagnosis List

Final Diagnosis

Osteomyelitis pubis with bilateral hip adductor and rectus abdominis abscesses.

URL:	https://eurorad.org/case/15211
DOI:	10.1594/EURORAD/CASE.15211
ISSN:	1563-4086