46 - Neuromuscular Effects from a Giant Lipoma in the Arm

Poster Board Number: 46
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Abstract Body : Introduction: Lipomas are slow growing, mesenchymal fatty tumors derived from primordial adipocytes, hereditary disorders, or trauma. They most often develop in subcutaneous regions of the head, neck, back, abdominal wall, and thigh, but they can develop in subfascial intermuscular, intramuscular, or parosteal regions and are rarely associated with the upper limb. Most are benign, but lipomas reaching 5 cm or greater in any one dimension are deemed “giant lipomas” and warrant histopathological examination for malignancy and subtype characterization. Albeit rare, giant lipomas of the upper limb are well represented in clinical literature, but report of one that had never been surgically excised with gross imaging of neuromuscular effects would present new information to the field. The objective of the present study was to analyze the neuromuscular effects of an intermuscular giant lipoma in the arm.

Methods: A giant intermuscular lipoma in the anterior compartment of a left arm was discovered during routine dissection on an embalmed human cadaveric donor. The dissection field was cleaned of extraneous tissue and the lipoma was photographed in situ. Ultrasonography was used to determine lipoma consistency and the respective course of the musculocutaneous nerve. The angles of the biceps brachii and coracobrachialis muscles over the lipoma were measured, and the lipoma was removed, measured, weighed, and photographed. The biceps brachii and coracobrachialis muscles were removed bilaterally and analyzed for fascicle length, muscle belly mass, and sarcomere fixation lengths (via light microscopy). Fascicle lengths were normalized, and maximal isometric force (Fmax) and torque capabilities were calculated for each muscle.

Results: The lipoma developed between the biceps brachii, coracobrachialis, musculocutaneous nerve, and the shaft of the humerus. It displaced the biceps brachii muscle laterally, arching the short head over it and causing significant visible stretching of the coracobrachialis muscle and musculocutaneous nerve around its medial border. The 18.4 cm long, 318.65 g, ovate lipoma increased left biceps brachii’s angle of attachment to the radial tuberosity from 7.4° to 14.9°, essentially doubling its torque capability on the radius (38.26 N·cm to 76.39 N·cm), whereas the right biceps brachii exhibited typical attachment angle (7.4°) and torque (29.97 N·cm). The left and right coracobrachialis exhibited similar Fmax (18.00 N and 16.88 N, respectively), but the lipoma caused the left one to exhibit a significantly larger angle of attachment (34.6° vs. 15.1°) and torque producing capability (114.48 N·cm vs. 49.25 N·cm). Aside from an additional belly on the left biceps brachii long head and the angular impacts (from the lipoma) on the left biceps brachii and coracobrachialis insertions, the muscles and their biomechanics would have been comparable bilaterally.

Conclusions: Subfascial intermuscular giant lipomas of the arm present many clinical implications. While aesthetics and irritation from the sizable mass are often chief complaints, this study shows how nerve impingement and biomechanical impact are also likely to result. The gross and ultrasound imaging and analyses presented in this study may inform physicians when working to diagnose and treat giant lipomas, hereditary multiple lipomatosis, adiposis dolorosa, Madelung’s disease, and other related conditions.