Obturator Internus Abscess: Spontaneous Perforation into the Vagina

Abstract

A17-year-old girl reported to the emergency department, with left hip pain and a limp of 15 days' duration. She had no recent history of trauma, recurrent fever, sore throat, diarrhea, easy bruising, rash, or multiple joint pain. On physical examination her left hip was found to be in mild flexion at rest, with restricted movement. There was local tenderness and swelling over the left groin and edema of the left labia majorum. There was no distal neurovascular deficit. Plain radiographs of the pelvis and hips were normal. T2-weighted magnetic resonance imaging (MRI) showed a multilobulated abscess measuring approximately 11x6 cm involving the left obturator internus muscle and bulging into the left lateral vaginal wall, deviating it to the right. (Fig. 1). The mass extended laterally into the left obturator externus muscle. Edema was present in the intermuscular planes and muscles in the left proximal thigh and gluteal region, and the left labial fold was enlarged and edematous. No associated bony abnormality was identified. After being returned by wheelchair from the MRI suite to the emergency ward, the patient complained of passing a large volume of foul-smelling fluid vaginally, followed by immediate relief of the pain in her left hip and gluteal region. Blood and urine cultures of specimens of the fluid were sterile. A vaginal swab culture grew Escherichia coli. The patient was managed with an intravenous regimen of ceftriaxone 2 g/d in two divided doses and amikacin at 15 mg/kg/d as a single dose, with skeletal traction of her left lower limb. The patient's condition improved dramatically over the next 10 d, with disappearance of her limp and subsidence of her gluteal and vulvar edema. An ultrasonographic examination at 2 wks demonstrated no fluid collection in the patient's pelvis. She was discharged 15 d after her admission with instructions to follow a 4-wk course of oral ciprofloxacin (500 mg q12h). At 6 mos she was asymptomatic and involved in her normal daily activities.

FIG. 1.

T2-weighted magnetic resonance image showing a multilobulated abscess measuring approximately 11x6 cm, involving the left obturator internus muscle and bulging into the left lateral vaginal wall (white arrow) and deviating it to the right.

Discussion

Primary pyomyositis of the obturator internus muscle is the result of colonization of traumatized ischemic muscle during an episode of transient bacteremia [1]. Imaging is the mainstay of diagnosis because the clinical features of the condition are easily confused with other common causes of hip pain, and laboratory findings in the condition are often nonspecific. Magnetic resonance imaging is the modality of choice for imaging the obturator internus muscle and to ascertain the diagnosis of pyomyositis [2]. In a developing country such as India, where MRI is restricted to a few centers, a thorough clinical examination at the patient's bedside is invaluable for the diagnosis of pyomyositis of the obturator internus. Because of the close proximity of the muscle to the rectum and female reproductive organs, a routine digital rectal examination or vaginal examination can facilitate the diagnosis. The characteristic finding of a tender, fluctuant bulge of rectal or vaginal mucous membrane confirms the presence of a pelvic abscess and the need for prompt drainage. Also suggesting an abscess of the obturator internus in female patients is edema of the ipsilateral labia majorum [3]. The choice between medical and surgical management of an obturator internus abscess is guided by the clinical course of the disease and demonstration of a well-defined pus pocket on imaging studies. The patients with localized symptoms and signs who show no features of systemic toxicity and have no fluid collection in the area the of obturator muscles on imaging can be managed with a 2–4-wk course of intravenous antibiotics [3]. The lacki of a response to medical management, detection of a pus-filled cavity around the obturator muscles, and development of complications mandate surgical intervention. This can consist of image-guided percutaneous drainage or open surgical drainage of the abscess. Selection of the most appropriate access route is guided by precise location of the abscess cavity on imaging. Although all previously reported patients with obdurator internus abscess benefited by either medical or surgical intervention, ours is the first reported case in which spontaneous transvaginal rupture of the abscess during the natural progression of the condition had a favorable outcome.

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