AJR 2005; 184:S112-S114
© American Roentgen Ray Society
Obturator Neuropathy Caused by an Acetabular Labral Cyst: MRI Findings
Kiminori Yukata1,
Kazunori Arai2,
Yusuke Yoshizumi3,
Kenichi Tamano3,
Koichi Imada3 and
Norishige Nakaima3
1 Department of Orthopedics, School of Medicine, University of Tokushima,
3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan.
2 Department of Radiology, Kurobe City Hospital, Kurobe City, Toyama 938-8502,
Japan.
3 Department of Orthopaedic Surgery, Kurobe City Hospital, Kurobe City, Toyama
938-8502, Japan.
Received March 22, 2004;
accepted after revision June 1, 2004.
Address correspondence to K. Yukata
(kyukat{at}clin.med.tokushima-u.ac.jp).
Introduction
Cystic lesions around the hip joint associated with acetabular
labral tears are well documented and are called acetabular labral cysts or
acetabular paralabral cysts based on their anatomic relationship with the hip
joint [1,
2]. Peripheral nerve
compression caused by acetabular labral cysts can occur, and femoral or
sciatic neuropathy has been reported
[3,
4]. We report a case of an
acetabular labral cyst that resulted in symptomatic compression of the
obturator nerve.
Case Report
A 75-year-old woman presented with a 2-year history of increasing pain in
the right groin and anteromedial thigh with insidious onset. The patient had
no history of a traumatic event. On examination, the area over the right
adductor muscles was tender on palpation, and no sensory changes or weakness
of the adductor muscles was found. The patient had pain on abduction and
external rotation of the right hip, and she limped, circumducting the right
leg. Nonsteroidal antiinflammatory drugs did not alleviate the pain. MRI of
the lumbar spine showed no nerve-root compromise.
Radiographs of the hip showed a subchondral cyst at the acetabular rim and
no acetabular dysplasia. MRI of the pelvis revealed a cystic lesion arising
from the anterior aspect of the right acetabulum and extending medially into
the lateral wall of the lesser pelvis. A labral tear adjacent to the cyst was
diagnosed on the basis of MRI findings. The right external obturator,
adductor, and gracilis muscles innervated by the obturator nerve showed
increased signal intensity on STIR images and fatty atrophy on T1-weighted
images (Figs. 1A,
1B,
1C,
1D). Based on clinical and MR
findings, the diagnosis was obturator nerve entrapment caused by the labral
cyst. Using a sonographically guided technique, 2.5 mL of yellow, thick,
gelatinous fluid was aspirated from the cyst, after which the mass became
smaller (Figs. 2A,
2B).
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Fig. 1A. —75-year-old woman with pain in right groin and anteromedial
thigh. Coronal STIR image (TR/TE, 6,000/60; inversion time, 130 msec) shows
cystic lesion (arrowheads) on lateral wall of lesser pelvis and
increased signal intensity in external obturator and adductor muscles
(arrows).
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Fig. 1B. —75-year-old woman with pain in right groin and anteromedial
thigh. Axial STIR image (TR/TE, 6,000/60; inversion time, 130 msec) shows
increased signal intensity in external obturator and adductor muscles
(arrow).
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Fig. 1C. —75-year-old woman with pain in right groin and anteromedial
thigh. Axial T1-weighted spin-echo image (TR/TE, 715/20) shows atrophy with
fatty infiltration in adductor and gracilis muscles.
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Fig. 1D. —75-year-old woman with pain in right groin and anteromedial
thigh. Sagittal oblique multiecho data image combination gradient-echo image
(TR/TE, 775/27; 30° flip angle) obtained in section parallel to right
femoral neck shows labral structure that is not clearly depicted in anterior
hip joint (arrowhead), typical characteristic of labral tear. A stalk
of cystic lesion continues to anterior labrum (arrows).
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Fig. 2A. —75-year-old woman with pain in right groin and anteromedial
thigh. Sonograms before (A) and after (B) cyst aspiration
(arrows). Distance between asterisks shows diameter of cyst (distance
between point is 10 mm).
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Fig. 2B. —75-year-old woman with pain in right groin and anteromedial
thigh. Sonograms before (A) and after (B) cyst aspiration
(arrows). Distance between asterisks shows diameter of cyst (distance
between point is 10 mm).
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Four days after the aspiration, the patient's pain had diminished and she
could walk without a cane. Four weeks later, she had recovered full range of
motion of the right hip and could walk normally without pain. At the most
recent follow-up 8 months after the aspiration, the patient was
asymptomatic.
Discussion
Obturator neuropathy can be caused by a pelvic fracture, hip arthroplasty,
abdominal or pelvic surgery, forceps delivery, lithotomy position, pelvic
tumor, and obturator hernia. To our knowledge, acetabular labral cyst as the
cause of obturator neuropathy has not been previously reported in the
literature.
The most prominent symptom of obturator neuropathy is pain radiating from
the groin into the medial upper aspect of the thigh. Dysesthesia and weakness
of the muscles supplied by the obturator nerve can occur if the neuropathy is
severe [5]. Our patient had the
characteristic symptoms of obturator neuropathy. The clinical diagnosis of
obturator neuropathy was supported by a decreased volume of the muscles
supplied by the obturator nerve on MRI
[6]. The muscles showed
increased signal intensity on T2-weighted images, indicating acute
denervation, atrophy with fatty infiltration, and chronic denervation.
The obturator nerve arises from the second, third, and fourth lumbar
nerves; descends into the psoas major muscles; and follows the lateral wall of
the lesser pelvis until it reaches the upper obturator foramen. MRI showed
that, in our patient, the location of the cyst was consistent with the region
of the obturator nerve on the lateral wall of the lesser pelvis. Based on
these findings, we believe the cyst developed as a result of a labral tear or
an intraosseous cyst. Although it could be considered an acetabular labral
cyst, an accurate diagnosis would require MR arthrography to show the
communication between the cyst and the joint
[7].
The recurrence rate of labral cysts of the shoulder after aspiration is
reported to be high. Therefore, the definitive treatment for acetabular labral
cysts is to repair the labral tear that caused the cysts
[8]. However, the preferred
initial treatment for a labral cyst of the hip is percutaneous aspiration
because of its low invasiveness and dramatic effect, as seen in our case.
Acknowledgments
We are grateful to Shinsuke Katoh and Yoshito Matsui, Department of
Orthopedics, The University of Tokushima, for their critical review of the
manuscript.
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Introduction
Case Report
