Minimally Invasive Resection of a Large Subcutaneous Lipoma: The 2.5-cm (1-inch) Method.

Background: Lipomas are benign and are usually located in subcutaneous tissues. Surgical excision frequently requires an incision equal to the diameter of the lipoma. However, small incisions are more cosmetically pleasing and decrease pain and/or hypoesthesia at the incision. A "fibrous structure" occurs inside the lipoma and is characterized by a low-intensity signal on T1-weighted magnetic resonance images. The "fibrous structure" is actually retaining ligaments with a normal structure that intrudes from the periphery¹. Retaining ligaments are fibrous structures that are perpendicular to the skin and tether it to underlying muscle fascia.

Description: The peripheral border of the tumor is marked with a surgical pen preoperatively. Under general anesthesia, a 2.5-cm (1-inch) incision is made with a surgical knife, cutting into the tumor through the capsule-like structure. Distinguishing the tumor from the overlying adipose tissue can be difficult. Use of only local anesthesia may be possible when the number of retaining ligaments is low, such as for lesions involving the upper arm. A central incision is preferred; a peripheral incision is possible but can make the procedure more difficult. Detachment of the lipoma from the retaining ligaments is performed bluntly with a finger, which allows pulling the tumor out between the retaining ligaments. We use hemostat forceps (Pean [or Kelly] forceps) to facilitate blunt dissection. Hemostat forceps are usually utilized for soft-tissue dissection and for clamping and grasping blood vessels. Prior to blunt dissection, dissection with Pean forceps can be performed over the surface of the tumor, but tearing the tumor apart can also be useful to allow subsequent finger dissection of the lipoma from the retaining ligament not only from outside but also from inside the lipoma. The released lipoma is extracted in a piecemeal fashion with Pean forceps or by squeezing the location to cause the lipoma to extrude through the incision. The retaining ligament is preserved as much as possible, but lipomas are sometimes completely trapped by the retaining ligament. In such cases, partially cutting the ligament with scissors to release the tumor can be useful during extraction. Detachment and extraction are repeated until the tumor is completely resected, which can be confirmed visually through the incision because of the resulting skin laxity. Remaining portions of a single lipoma are removed with Pean forceps. The residual lipomas may be located deep to the retaining ligament. Adequate lighting and visualization through a small incision is useful. After the skin is sutured, a Penrose drain is optional.

Alternatives: The squeeze technique utilizing a small incision over the lipoma is a well-described technique for forearm or leg lipomas, but is often not successful for large lipomas, especially those in the shoulder. The squeeze technique is not always successful in these cases because of the fibrous structure, which is actually retaining ligaments¹. Liposuction has also been reported as a minimally invasive treatment; however, long-term results of liposuction are disappointing with respect to the completeness of the resection and frequency of side effects, especially when the lipoma is fibrous.

Rationale: The retaining ligaments are not truly linear but rather membranous, continuous with the surrounding normal tissues, and located at the periphery of the lipoma. Detachment of the lipoma from the retaining ligaments with a finger allows for extraction of the lipoma in a piecemeal fashion or via the squeeze technique through a small incision. Subcutaneous fibrous structures are reportedly highest in concentration for lateral and posterior lesions, with the density gradually increasing as lesions move posteriorly². The operative time for the 1-inch method is longer for lipomas of the torso than those of the shoulder or extremities because the number of retaining ligaments is higher in the back. We assessed 25 patients with large lipomas, defined as a tumor diameter >5 cm. The mean operative time for all lesions was 28 minutes, with a mean time of 26 minutes for lipomas at the shoulder, 22 minutes for the extremities, and 47 minutes for the torso³.

Expected outcomes: The blunt procedure may cause dull pain at the tumor site for approximately 1 week. The skin-retaining ligaments at the periphery of the lipoma may serve to warn of the locations of peripheral nerve branches. Preserving the retaining ligaments decreases the possibility of hypoesthesia or permanent chronic pain at the incision site¹. The 1-inch method is indicated in cases with a large subcutaneous lipoma. The maximum lipoma size for this procedure has not been established; however, because of skin laxity, we have not had difficulty reaching the peripheral parts of a lipoma, even if it is >10 cm in diameter, with use of the 1-inch method.

Important tips: Lipomas involving the back take more time than shoulder or extremity lipomas.The peripheral border of the tumor is marked.The incision is made with a surgical knife from the skin to the inside of the tumor.The lipoma is detached from the retaining ligaments with a finger, and the tumor is pulled between the retaining ligaments.The lipoma is extracted in a piecemeal fashion or using the squeeze technique.Complete resection is confirmed visually through the incision, which is possible because of the skin laxity.

Acronyms and abbreviations: MRI = magnetic resonance imagingSTIR = short-tau inversion recovery.