Intraneural Lipoma of the Ulnar Nerve

Abstract

Sir: A 9-year-old girl presented with exertional discomfort of the right hand due to two slowly enlarging masses. There was no history of trauma, paresthesias, numbness, or weakness. Clinical examination revealed two discrete masses, one proximal to the flexor wrist crease measuring 5 × 1.5 × 0.5 cm and a second measuring 7 × 4 × 2 cm in the hypothenar eminence (Fig. 1). The masses were soft and mobile, with well-defined borders and no overlying skin changes. The Tinel sign was absent. An Allen's test demonstrated the ulnar artery of the hand to be patent, but with delayed filling.Fig. 1.: Gross appearance of the right wrist and hypothenar eminence masses of the right hand, measuring 5 × 1.5 × 0.5 cm and 7 × 4 × 2 cm, respectively. Intraoperative markings demonstrate the location and extent of the lesion. A single incision was made directly over the lesion and crossing the flexor wrist crease, as shown.Magnetic resonance imaging was consistent with a lipoma in the volar aspect of the right wrist and hand with displacement of the flexor digitorum superficialis tendons. Magnetic resonance angiography revealed radial displacement of the ulnar artery. At exploration, the mass appeared to be a large, multilobulated lipoma originating from within the ulnar nerve, with splaying of fascicles and attenuation of the hypothenar musculature. The ulnar artery was displaced radially. Resection yielded a 14-cm multilobulated mass with no residual lesion (Fig. 2). All nerve and fascicle groups, the ulnar artery, and the palmar arch were left intact.Fig. 2.: With the mass completely removed, the splayed, intact fascicles of the ulnar nerve are visible. The incision was closed directly without removing excess skin.Gross pathologic examination revealed an encapsulated, lobulated mass of homogeneous adipose tissue. Microscopic findings showed mature fibroadipose tissue consistent with the diagnosis of a benign intraneural lipoma. Postoperative evaluation at 2 weeks showed normal median and ulnar nerve function, with only mild weakness of the abductor digiti minimi. Follow-up at 1 month showed increased range of motion, improved ulnar sensation, and persistent, mild, residual small-finger weakness on abduction. Masses originating in the median and ulnar nerves are exceedingly rare.1,2 The nomenclature for such masses has been based primarily on pathologic descriptions, such as lipoma, intraneural lipoma, lipofibromatous hamartoma, fibrofatty proliferation, and fatty infiltration.1,3,4 Intraneural lipofibromas have been divided into three major entities based on pathologic descriptions and clinical/anatomical behavior: true intraneural lipomas, lipofibromas, and peripheral nerve hamartomas with marcrodactyly.3 True lipomas are soft, noninvasive, encapsulated tumors that displace adjacent structures. These lesions can be readily dissected from surrounding tissues and histologically contain fibrous and fatty tissue, but lack neural elements. Distinct from true lipomas, lipofibromas contain fibrous, fatty, and neural elements. Confined within the nerve sheath, lipofibromas are often impossible to separate from nerves without extensive interfascicular dissection or complete nerve resection. Nomenclature varies and includes the pseudonyms fibrofatty proliferation, intraneural lipoma, and lipomatous hamartoma. Hamartomas represent a third entity of benign tumors, similar to lipofibromas histologically in that they both contain fibrous, fatty, and neural elements. Some authors propose nomenclature that combines associations with macrodactyly: lipofibromatous hamartoma with or without macrodactyly.1,2 Patients present in childhood with swelling of the wrist or hand and varying degrees of compressive symptomatology. Magnetic resonance imaging is typically diagnostic but cannot delineate the degree of fascicular involvement.5 Operative exploration is indicated for progressive mass enlargement, overt compressive symptoms, and histopathologic confirmation. Depending on the anatomical relationship of the lesion, surgical treatment may involve biopsy and ligamentous decompression, limited interfascicular dissection, complete resection with nerve grafting, complete resection, and, occasionally, compensatory tendon transfer. In summary, benign, fibrofatty tumors of the hand and wrist are indeed rare. Associated symptoms are directly related to tumor size and anatomic location. The natural history is continued growth and potential exacerbation of symptoms without spontaneous regression.4 Surgical intervention should be considered in patients with large or indeterminate masses. Treatment by excision should be considered early in the disease process. Laura A. Bonneau, Stephen J. Delatte, M.D. Michael L. Bentz, M.D. Division of Plastic Surgery Department of Surgery University of Wisconsin-Madison Madison, Wis.