August 2008 - Proscan Imaging

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August 2008 Case of the Month

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Compiled by: Warren Martin, MD

History: 34 year old male with decreased shoulder strength for several months and a pre-MRI electromyelogram demonstrating suprascapular neuropathy.

Exam: MR arthrogram of the right Shoulder.

Findings: Figure 1, a T1 sagittal image, partially demonstrates a SLAP type tear of the labrum that extends posterior from the biceps anchor approximately two centimeters to the nine o�clock position of the posterior labrum. From this tear, as seen on Figure 2, an axial T2 image, extends an approximately 3 cm multilobulated paralabral cyst that fills the spinoglenoid notch. In figure 3, an axial T1 image, the cyst (green arrow) is seen to contact the suprascapular neurovascular bundle (orange arrow) in the suprascapular notch. The sagittally acquired SPIR image, Figure 4, demonstrates the cyst (orange arrow) insinuating between the supraspinatus and infraspinatus muscle bellies and also demonstrates subtle edema within the infraspinatus muscle (green arrows). An additional post-arthrogram coronal SPIR image, figure 5, demonstrates superior to inferior extent of the cyst.

Images: Figure 1: T1 sagittal image. Figure 2: axial T2 image. Figure 3: axial T1 image. Figure 4: sagittally acquired SPIR image. figure 5: post-arthrogram coronal SPIR image.

Figure 1	Figure 2
Figure 3	Figure 4
Figure 5

Diagnosis: Posterior superior labral tear with a three centimeter paralabral cyst extending into both the spinoglenoid and suprascapular notches

Discussion: The suprascapular nerve arises from the superior trunk of the brachial plexus and courses beneath the transverse scapular ligament, the roof of the suprascapular notch, to enter the supraspinatus fossa. Here the nerve gives off two motor branches to innervate the supraspinatus muscle and sensory branches to the glenohumeral and acromioclavicular joints. The nerve then passes posterior and inferior through the spinoglenoid notch to innervate the infraspinatus muscle via two to four motor branches, within the infraspinatus fossa. The suprascapular nerve has no cutaneous sensory component.

Suprascapular nerve compression syndrome occurs secondary to lesions affecting the suprascapular nerve along its course from the suprascapular notch to the infraspinatus fossa. Compressive lesions that extend superiorly to the suprascapular notch can cause edema and atrophy of both the supraspinatus and infraspinatus muscles, and often nonspecific shoulder pain, while lesions within the spinoglenoid notch typically cause abnormalities within only the infraspinatus muscle.

The clinical diagnosis of suprascapular nerve palsy or evidence of supra- and/or infraspinatus muscle edema or atrophy on shoulder MRI should therefore prompt a search for compressive lesions along the course of the suprascapular nerve. These lesions may include cysts, masses, sequela of prior trauma, thickening of the transverse scapular ligament, and varices. However, the most common finding is that of a paralabral cyst.

Paralabral cysts are usually seen in association with posterior capsulolabral injuries. They expand as fluid extends through a labral tear and becomes trapped, via a �ball and socket� mechanism, within the cyst. Cysts that arise from the posterior joint are often �funneled� between the supraspinatus and infraspinatus muscles as a path of least resistance, to the spinoglenoid and then suprascapular notch.

Initial treatment is aimed at relief of mass effect, via cyst aspiration; however treatment of the underlying labral tear may be indicated should the patient remain symptomatic.

References:

1. Stoller D, Tirman P, Bredella M. "Diagnostic Imaging, Orthopaedics." Salt Lake City: Amirsys, 2004.

2. Stoller D, Wolf E, Li A, Nottage W, Tirman P. �Paralabral Cysts and Suprascapular Nerve Entrapment�. Magnetic Resonance Imaging in Orthopaedics and Sports Medicine. Baltimore: Lippincott Williams, and Wilkins, 2007;1408-1413.