Painful intramuscular lipoma of the thigh.

Abstract: Intramuscular lipomas of the extremities are most often found in the thighs and shoulders. They are usually painless, but described herein is a case of extreme leg pain that was relieved when a lipoma in the thigh was identified and surgically resected.

Key Words: lipoma, lower extremity, muscle neoplasms

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Deep-lying lipomas of the extremities are usually found in the thighs or shoulders. These benign growths may be intermuscular or intramuscular (IM) and are most often discovered incidentally or during evaluation of a usually painless swelling. (1) This report describes the occurrence of exquisite pain and tenderness related to an IM lipoma of the thigh.

Case Report

A 70-year-old woman with a history of osteoporosis, hypertension, and treated hyperparathyroidism underwent successful surgery for adhesive capsulitis of the shoulder. After surgery, a sense of numbness of the right lateral thigh was noted, and over the next 4 weeks shooting pains occurred in the same area. A vague swelling and exquisite tenderness, with the patient unable to bear even light touch, were found over the vastus lateralis muscle. Vascular and orthopaedic examinations were otherwise normal. Examination with magnetic resonance imaging (MRI) showed a well-demarcated mass in the right lateral thigh, consistent with a deep lipoma (Fig. 1). Because of severe and disabling pain, surgical exploration was undertaken. The mass was completely excised, and was found to be an IM lipoma with no sarcomatous features (Fig. 2). No involvement of nerve tissue was evident. At follow-up, 11 days after surgery, all pain was gone.

[FIGURE 1 OMITTED]

Discussion

The locations and clinical features of deep-lying lipomas of the extremities have been well described. (1) Intermuscular lipomas are found in the planes between muscles. IM lipomas infiltrate skeletal muscle and may locally recur if they are not completely excised. (2) The magnetic resonance features of these tumors have been reported and can be helpful in distinguishing benign lipomas from malignant liposarcomas. (3) Surgery, however, is often needed to confirm the benign nature of these growths, and extensive resection may be necessary to avoid recurrence. (4) Histologic examination of IM lipomas can show infiltration of skeletal muscles, with strips of preserved muscle fibers traversing adipose tissue, as shown in Figure 2. (1) This appearance is indicative of a benign neoplasm of fat tissue.

Pain is said to be infrequent with these lipomas, although cases in which patients did have significant pain have been reported. Gold and Oppenheim (5) reported disabling arm pain and paresthesias associated with an intermuscular lipoma of the forearm. Irritation of an "intimately related" nerve was the suspected cause of symptoms. Leffert's (6) series of 141 upper extremity lipomas included 26 causing pain and 6 causing nerve compression, but how many were deep lipomas was not made clear. Bjerregaard et al (4) reported that one of his 12 patients with deep lipomas of the thigh had pain sufficient to inhibit function of the leg, and Warner et al (7) described two cases of shoulder pain related to IM lipomas of the deltoid muscles.

[FIGURE 2 OMITTED]

Conclusion

Dramatic pain of the sort experienced by our patient has not been previously described. Her pain began only after positioning for shoulder surgery, and some undefined interplay between the lipoma and this positioning appears to have triggered her distress. Stretching or irritation of a nearby nerve was considered likely, but no evidence of such was found at surgery. Whatever the mechanism, it is clear that our patient's disabling discomfort was relieved by identification and excision of a deep IM lipoma of the thigh.

Success usually comes to those who are too busy to be looking for it.
--Henry David Thoreau

Acknowledgments

The author acknowledges the assistance provided by Richard Pierce, MD, who prepared the photomicrographs, and by John Parenti, MD, who was the attending orthopaedist who removed the tumor described in this paper.

Accepted January 8, 2004.

References

1. Kindblom L-G, Angervall L, Stener B, et al. Intermuscular and intramuscular lipomas and hibernomas: a clinical, roentgenologic, histologic, and prognostic study of 46 cases. Cancer 1974;33:754-762.

2. Austin RM, Mack GR, Townsend CM, et al. Infiltrating (intramuscular) lipomas and angiolipomas: a clinicopathologic study of six cases. Arch Surg 1980;115:281-284.

3. Matsumoto K, Hukuda S, Ishizawa M, et al. MRI findings in intramuscular lipomas. Skeletal Radiol 1999;28:145-152.

4. Bjerregaard P, Hagen K, Daugaard S, et al. Intramuscular lipoma of the lower limb: long-term follow-up after local resection. J Bone Joint Surg Br 1989;71:812-815.

5. Gold AM, Oppenheim A. Deep intermuscular lipoma of an extremity: a case report. J Bone Joint Surg Am 1954;36:146-148.

6. Leffert RD. Lipomas of the upper extremity. J Bone Joint Surg Am 1972;54:1262-1266.

7. Warner JJP, Madsen N, Gerber C. Intramuscular lipoma of the deltoid causing shoulder pain: report of two cases. Clin Orthop 1990;253:110-112.

RELATED ARTICLE: Key Points

* Deep lipomas may be intermuscular or intramuscular.

* Diagnosis of these benign neoplasms is facilitated by magnetic resonance imaging.

* Most deep lipomas are painless, but severe pain can sometimes occur.

David R. Gutknecht, MD

From the Department of General Internal Medicine, Geisinger Medical Center, Danville, PA.

Reprint requests to David R. Gutknecht, MD, Department of General Internal Medicine, Geisinger Medical Center, Danville, PA 17822-1401. Email: [e-mail]