Lipomatous Mass Effect on the Brachial Plexus: A Case Report

Peripheral nerve compression is a prevalent concern for primary care physicians and hand surgeons, with carpal tunnel syndrome (CTS) and median nerve compression at the wrist being some of the most commonly diagnosed conditions. However, for less common nerve entrapment syndromes, it is crucial for healthcare providers to recognize their symptoms and consider potential underlying issues, particularly those related to the brachial plexus. This case report highlights a 57-year-old male who presented with classic symptoms of left median and ulnar nerve compression in the setting of an enlarging left axillary mass. The patient, a right-hand-dominant male, reported numbness and tingling in the left ulnar-sided digits, as well as weakness in small and ring finger flexion, which began after a fall onto his elbow and outstretched hand a year prior. Initially, the patient experienced significant numbness, tingling, and pain radiating up to the shoulder. Weakness in hand grip, especially affecting the small and ring fingers, and thumb abduction and opposition were also noted. The patient reported transient symptomatic relief with shoulder abduction. Over time, his median nerve compression symptoms improved, with only mild residual tingling noted with shoulder adduction and compression of the axillary mass. However, his ulnar nerve compression symptoms showed minimal improvement despite occupational therapy. The patient had a history of a left axillary lipoma identified five years earlier, which had not been surgically treated, aside from an incisional biopsy that confirmed the pathology. Upon examination, the patient presented with a 7 cm × 10 cm, well-circumscribed, deeply adherent mass in the left axilla. Clinical findings included a positive Wartenberg's sign of the left small finger, decreased strength in small and ring finger flexion compared to the right, and impaired two-point discrimination of the small and ring fingers. A positive Tinel's sign was noted at the left cubital tunnel, while the carpal tunnel and Guyon's canal were negative. Electromyography revealed left-sided ulnar and median nerve compression at the cubital tunnel and carpal tunnel, but could not exclude brachial plexopathy. MRI of the left brachial plexus revealed the lipoma exerting mass effect on the brachial plexus cords and branches, as well as the left axillary vasculature. Surgical intervention involved excision of the left axillary lipoma, brachial plexus exploration and neurolysis, and cubital tunnel release with anterior transposition. Three lipomatous masses were identified, intertwined with the brachial plexus divisions and cords and the axillary vasculature. Meticulous dissection with 3.5× loupe magnification was performed to decompress the brachial plexus. At the six-month follow-up, the patient's symptoms had completely resolved, and he returned to full activity. This case underscores the importance of evaluating and ruling out brachial plexus pathology in patients presenting with peripheral nerve compression symptoms.