Case Report
MRI of Piriformis Syndrome
Edward Y. Lee1, Anthony J. Margherita2, David S. Gierada1, Vamsi R. Narra1
P iriformis syndrome is a rare cause
of lower back pain and sciatica
secondary to sciatic nerve entrap-
ment at the greater sciatic notch [1]. It is usu-
radicular provocation test findings were normal.
Flexing the hip at 90° and adducting across the
midline with deep digital palpation produced ex-
quisite tenderness in the right piriformis muscle
appearance and location. However, it was
compressed by the piriformis muscle crossing
anterior to the right S2 nerve root. The S2
nerve was surgically released and appeared
ally caused by an abnormal condition of the that reproduced the patient’s pain. Passive inter- slack after approximately 1 cm of the pirifor-
piriformis muscle such as hypertrophy, inflam- nal rotation of the right thigh caused pain (Fri- mis tendon was resected near its insertion at
mation, or anatomic variations [1]. We report berg’s sign), as did resistance to abduction and the piriformis fossa.
the case of a 40-year-old man with piriformis external rotation of the right thigh (Pace’s sign) The patient reported complete relief of
syndrome secondary to an anomalous sacral and voluntary adduction, flexion, and internal ro- symptoms immediately after the operation.
attachment of an otherwise normal piriformis tation of the hip (Lasègue’s sign). Neurologic and The postoperative course was uneventful.
muscle that was revealed on MRI and con- vascular examinations showed no abnormality. One month after surgery, the patient’s lower
firmed at surgical repair. Although it has been Imaging studies were all unremarkable, in- back pain and right lower limb symptoms
known as a cause of lower back pain and sciat- cluding conventional radiographs of the pel- had not returned. The patient had a mini-
ica since it was first described by Yeoman [2] vis, lumbar spine, sacrum, and coccyx; a mally reduced range of right hip flexion, ad-
in 1928, piriformis syndrome is frequently triple-phase bone scan; and MR images of the duction, and internal rotation, but these
misdiagnosed or the correct diagnosis is de- lumbar spine. The findings of electromyogra- maneuvers did not elicit the previous symp-
layed because of its rarity, nonspecific clinical phy were normal. The patient also underwent toms. Five years later, the patient’s symp-
symptoms, and absence of definite diagnostic a diagnostic trigger point injection with little toms have not recurred.
tests [1]. Familiarity with this syndrome and or no benefit. It was believed that the patient’s
its imaging findings is important for making symptoms were likely the result of either lo- Discussion
the correct diagnosis. cal spasm of the piriformis muscle or pirifor- The piriformis syndrome is a rare entrap-
mis syndrome. ment neuropathy in which the sciatic nerve is
Case Report The patient was referred for an MRI of the compromised by an abnormal piriformis mus-
A 40-year-old man was referred to a physi- sacral plexus with attention focused on the pir- cle. Approximately 6% of lower back pain and
atrist for chronic pain in the right buttock ra- iformis muscle, to narrow the possibilities. sciatica cases seen in a general practice may be
diating to the posterior thigh and groin that This study showed an anomalous sacral attach- caused by piriformis syndrome [3]. Piriformis
had been increasing during the previous 10 ment of the right piriformis muscle, with ac- syndrome is characterized by pain and pares-
months. The patient’s pain increased after cessory muscle fibers extending medially over thesias in the unilateral gluteal region radiat-
prolonged sitting, walking, and climbing the S2 foramen and crossing over the right S2 ing to the hip and posterior thigh in a sciatic
stairs. He denied any motor deficits, sensory nerve (Fig. 1). The piriformis muscle and sci- radicular distribution [4]. At physical exami-
symptoms, or bladder symptoms. He tried pe- atic nerve were normal in signal intensity on nation, the patient’s symptoms can be repro-
riods of rest and over-the-counter analgesic T1- and T2-weighted sequences. No other duced by digital pressure over the belly of the
medication, but the pain had become progres- abnormalities in anatomic relationships with piriformis muscle in the gluteal region and
sively worse. Treatment with a variety of the surrounding structures were found. also by digital pressure on the lateral pelvic
nonsteroidal antiinflammatory agents and The patient underwent surgical exploration wall of the affected side during rectal or pel-
gabapentin yielded no long-term benefit. through an incision extending from the poste- vic examination.
At physical examination, the lumbar spine rior superior iliac spine to the greater tro- No definite causative factors are known for
was not tender and had full range of motion. All chanter. The sciatic nerve was normal in this syndrome, but the usual source is thought
Received March 11, 2003; accepted after revision October 21, 2003.
1
Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd., Box 8131, St. Louis, MO 63110. Address correspondence to E. Y. Lee
(Leeed@mir.wustl.edu).
2
Department of Anesthesiology, Washington University School of Medicine, MSK Health, Wellness, and Rehabilitation, 11652 Studt Ave., St. Louis, MO 63141.
AJR 2004;183:63–64 0361–803X/04/1831–63 © American Roentgen Ray Society
AJR:183, July 2004 63
Lee et al.
A B
Fig. 1.—40-year-old man with piriformis syndrome.
A, Unenhanced axial T1-weighted MR image of sacrum shows accessory fibers of right piriformis muscle (a) overlying right S2 nerve (arrow) and attaching medially. Note
that accessory fibers of right piriformis muscle and right S2 nerve are of normal signal intensity. p = normal left piriformis muscle at sacral attachment.
B, Unenhanced oblique coronal T1-weighted MR image shows accessory fibers of right piriformis muscle (a) anterior to and obscuring right S2 nerve. p = normal right and
left piriformis muscles.
to be traumatic injury to the piriformis muscle entity in which the nerve becomes compressed piriformis syndrome on MRI is important to fa-
that results in spasm, edema, and contractures during prolonged sitting, walking, running, or cilitate appropriate diagnosis and treatment.
of the muscle and causes subsequent compres- other exercise. It is possible that the sciatic
sion and entrapment of the sciatic nerve [5]. nerve was not compromised by the piriformis Acknowledgment
Other possible causes of this syndrome include muscle while the patient was lying comfort- We thank Mehdi Poustchi-Amin for read-
reflex spasm of the piriformis muscle and an ably on the MRI table. Furthermore, our pa- ing our initial manuscript.
abnormal course of the sciatic nerve through tient had been limiting physical activities that
the piriformis muscle [6] or its tendon [1]. Al- might precipitate his symptoms for approxi- References
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