An uncommon cause of an uncommonly diagnosed shoulder pain

Clinical History

A 31-year-old patient came with complaints of weakness of left upper limb for one month, with difficulty in lifting heavy objects. No history of numbness/tingling sensation. On clinical examination, power was 3/5 with sluggish triceps reflex. The sensory system was intact.

Imaging Findings

Prior to imaging, the patient underwent a nerve conduction study which was normal. Radiography of the left shoulder was unremarkable. Due to the persistence of complaints the patient underwent an MRI scan.
A well-defined cystic lesion seen in the suprascapular notch and spino-glenoid notch. The lesion appears T1 hypointense and hyperintense on T2. On postcontrast scan, the lesion shows peripheral enhancement with a central non-enhancing area.

Discussion

- Background: Supra-scapular nerve arises from the upper trunk of brachial plexus and is mainly supplied by C5, C6 and sometimes by C4. It has mixed sensory and motor supply. At the level of supra-scapular fossa, the nerve gives a motor branch to the supraspinatus and receives a sensory branch from the surrounding glenohumeral and acromioclavicular joint [1]. At the infraspinatus fossa, the nerve is purely motor with supply to infraspinatus muscle.

- Clinical Perspective: Supra-scapular nerve compression is uncommon and uncommonly diagnosed due to non-specific findings. The supra-scapular nerve is vulnerable to entrapment neuropathy at the supra-scapular notch and spino-glenoid notch to a narrow fibro-osseous tunnel. Various causes of compression include paralabral cyst, lipoma, haematoma, and malignant neoplasms [2, 3].

- Imaging Perspective: Diagnosis is based on the clinical features, electromyography findings, and imaging. MRI is the modality of choice in these cases. Compressive neuropathy presents with direct and indirect signs. The direct signs are related to nerve findings including abnormalities in size, position, and signal changes [4]. Indirect signs are related to nerve denervation. Acute denervation presents with hyperintensity of the involved muscles (supraspinatus and infraspinatus muscle) and chronic denervation presents with loss of muscle bulk and fatty infiltration. Ganglia appear hypo to isointense on T1, hyperintense on T2 and peripheral enhancement on post-contrast phase.

Ganglia can be treated by either arthroscopic approach or open repair for cyst decompression/excision and associated labral tears.

Differential Diagnosis List

Final Diagnosis

Suprascapular nerve entrapment secondary to ganglionic cyst

URL:	https://eurorad.org/case/15610
DOI:	10.1594/EURORAD/CASE.15610
ISSN:	1563-4086