A Benign Soft Tissue Mass Simulating a Glenoid Labral Cyst on Unenhanced Magnetic Resonance Imaging

Military Medicine, May 2004 by Sherman, Paul M, Sanders, Timothy G, De Lone, David R

A 72-year-old Caucasian man initially presented with a vibratory sensation progressing to pain in his left scapular region. After failed conservative therapy, a left shoulder unenhanced magnetic resonance (MR) imaging study was performed. Initial interpretation suggested a glenoid labral tear with an associated paralabral cyst. Further review of the images identified heterogeneous increased T2-weighted signal intensity, which led to repeat MR imaging with intravenous contrast and the diagnosis of a solid tumor in the suprascapular notch. The MR appearance of the mass is illustrated and the usefulness of intravenous contrast administration in differentiating between a solid and cystic mass on MR imaging is discussed.

Introduction

Glenoid labral cysts are commonly identified adjacent to the glenoid labrum on MR imaging of the shoulder and these cysts are frequently associated with labral tears and glenohumeral instability. However, the unenhanced MR imaging findings of a solid mass can mimic a labral cyst and the possibility of a benign or malignant neoplasm should be considered in any case that demonstrates atypical imaging features.

Case Report

A 72-year-old Caucasian man reported an insidious onset of a vibratory sensation in the left scapular region, progressing to a sharp pain, while driving his automobile. The initial episode of pain lasted for approximately 30 seconds and recurred hourly. Over the next several months, the pain increased in duration and frequency until it was nearly constant. he presented to the internal medicine clinic 6 months after the initial onset of symptoms. Physical examination revealed a 2-cm palpable "knot" in the left trapezius muscle. There was mild weakness (4+/5) of left shoulder abduction, but the neurological examination was otherwise normal. Conventional radiographs of the left shoulder and cervical spine demonstrated mild glenohumeral and acromioclavicular joint degenerative change and degenerative disc disease without neuroforaminal narrowing. The patient was referred to physical therapy for stretching of the left trapezius muscle and rotator cuff strengthening exercises.

Magnetic resonance (MR) imaging was performed on the left shoulder after 3 months of physical therapy with no clinical improvement. Initial interpretation by a musculoskeletal radiologist suggested the diagnosis a superior labral tear with an associated labral cyst extending into the suprascapular notch. Upon further review of the images, it was noted that the internal signal of the presumed labral cyst was slightly heterogeneous on the T2-weighted images and the mass did not extend to the surface of the glenoid labrum (Fig. 1). Reevaluation of the glenoid labrum showed degenerative signal within the superior labrum without a definite tear. The patient returned for additional MR imaging with intravenous contrast. The heterogeneous region of increased T2 signal within the internal portion of the mass demonstrated moderate, heterogeneous enhancement. The well-circumscribed, oblong mass originated in the supraspinous fossa, passed through the suprascapular notch, and invaginated into the spinoglenoid notch, paralleling the course of the suprascapular nerve. There was widening of the spinoglenoid notch suggestive of pressure erosion (Fig. 2). The MR imaging characteristics seen after intravenous contrast administration are most consistent with a benign peripheral nerve sheath tumor (PNST) arising from the suprascapular nerve. However, differential considerations should also include other soft tissue masses such as synovial cell sarcoma, myxoid tumor, or a malignant nerve sheath tumor. The patient chose not to undergo biopsy of the mass at that time, and returned for follow-up MR imaging 8 months later. The imaging characteristics were unchanged and there was no increase in size of the mass. As the patient's symptoms had improved, he opted not to undergo biopsy or resection of the tumor. Although the presumed diagnosis based on MR findings is a benign nerve sheath tumor, the histologie diagnosis remains unknown.

Discussion

It has been well established that glenoid labral cysts are frequently associated with glenoid labral tears and shoulder instability.1 However, direct communication between the cyst and the joint space is only occasionally documented on MR imaging.2 Therefore, solid lesions that present in the vicinity of the glenohumeral joint that demonstrate low Tl- and high T2-weighted signal intensity, such as a PNST, myxoid tumor, or synovial cell sarcoma, potentially could be mistaken for a glenoid labral cyst on unenhanced MR imaging. Misdiagnosis on MR imaging of other cystic lesions that mimic a meniscal cyst around the knee have also been reported.3 Scapinelli3 reported two cases of synovial ganglia simulating meniscal cysts in the lateral knee compartment. The misdiagnosis of these labral or meniscal cysts could result in an inappropriate surgical procedure performed with the intention of repairing a labral or meniscal tear. Lewis and Reilly4 reported 36 cases of neoplasms that were misdiagnosed initially as sports related injuries. Failure to consider the possibility of a neoplasm, whether benign or malignant, may lead to diagnostic errors and subsequent inappropriate treatment.