Frontalis-associated lipoma: a rare case report.

Sir,

Lipomas are common benign soft-tissue neoplasms composed of fat cells. These tumors are often found where adipose tissue is present. They are the most common tumor of mesenchymal tissue and present as soft, immobile subcutaneous tumors that cause no symptoms, and as such, receive little attention from patients or physicians. However, they can be rarely found in intramuscular location and it is important to recognize this atypical presentation for two reasons. First, intramuscular lipomas may be confused with other swellings and second, attempts at surgical excision will be unsuccessful if carried out only into the subcutaneous tissue. We report a case of such rare occurrence of frontalis-associated lipoma.

A 58-year-old man presented with an asymptomatic swelling on the left side of forehead since 3 years with the gradual increase in size. Clinical examination revealed a 5 cm × 4.5 cm non-tender, firm, subcutaneous, slightly mobile swelling on the left side of forehead just above the eyebrow [Figure 1].

Figure 1

Well-defined, non-tender, slightly mobile, firm subcutaneous swelling on the left side of forehead

His routine investigations were within normal limits. With differential diagnosis of epidermoid cyst and lipoma, and surgical excision under local anesthesia was planned. After incising the skin and subcutaneous tissue, to our surprise, the plane of swelling was intramuscular [Figure 2]. Frontalis muscle was dissected to reveal a well-circumscribed yellowish mass, which was excised in toto [Figure 3] and sent for histopathological examination. The post-operative period was uneventful.

Figure 2

Yellowish mass seen after vertical separation of frontalis fibers, alongside supratrochlear nerve is seen

Figure 3

Complete removal of lipoma. Gross examination shows well-defined oval yellowish mass

The histology showed mature adipocytes in a connective tissue stroma surrounded by the fibrous capsule, without any cellular atypia or mitotic activity [Figure 4]. The lesion was diagnosed as “intramuscular lipoma.”

Figure 4

Lobules of adipocytes in connective tissue stroma

Lipoma is most common benign mesenchymal tumor. Solitary lipomas are classified into two types, superficial and deep seated/subfascial lipomas. Lipomas are rarely located within the muscles and between the muscles. The former is termed as “intramuscular lipoma” and later as “intermuscular lipoma.” Incidence of intramuscular and intermuscular lipomas is 1.8% and 0.3% of fatty tumors, respectively.[1] Such lipomas are seen in patients aged between 40 years and 70 years.[12] Among intramuscular lipomas, frontalis-associated lipoma is even rarer. On searching Pubmed, only two cases have been reported in literature so far.

Histopathologically, intramuscular lipoma can be of two types, well-circumscribed and infiltative types. Circumscribed type shows presence of fibrous capsule and composed of mature adipocytes similar to superficial lipoma, whereas infiltrative lipoma are associated with the muscle atrophy and degenerative changes.[1] The prognosis of frontalis associated lipoma is good and risk of recurrence is less provided there is complete surgical removal.

The first description of such kind of occurrence of lipoma in areas other than subcutis was reported by Uriburu in 1943.[3] The term “frontalis-associated lipoma” was coined by Salasche in 1989.[4]

Frontalis-associated lipoma arises in deeper tissue, as compared to traditional lipoma arising in subcutaneous tissue. They may arise in one of four locations: (1) within the frontalis muscle itself, (2) between the frontalis muscle and the deep investing fascia, (3) in the loose areolar tissue between the deep investing fascia of the frontalis muscle and the periosteum also called as “subgaleal lipomas,”[5] and (4) beneath the periosteum.[467] Lipoma of forehead also can occur in temporalis muscle as infiltrating lipoma.[78]

The knowledge of frontalis-assocaited lipoma is important in subcutaneous forehead nodules that may include epidermoid cyst, tumors such as osteoma, desmoids, and other fibrous tumor.[5] Removal of such intramuscular or deeper lipoma requires deeper incision onto fascia or muscle for complete excision than subcutaneous tumors. It helps the surgeon and the patient to be fore-warned about the depth and risk factors like damage to neuro-vascular bundles, muscle tissue and aponeurosis.

Conclusion

Subcutaneous forehead nodules are common. Knowing the differential diagnosis is critical for appropriate patient care. Frontalis-associated lipoma is one such differential to be kept in mind.