Lipomas are the most common benign soft-tissue mesenchymal tumors.¹ They are slow-growing, benign adipose lesions that form soft, lobulated masses enclosed by a thin, fibrous capsule. They have a prevalence rate of about 2.1 per 1000 population² and occur mostly in the fifth and sixth decades of life.³ Lipomas are uncommon in children. Males are affected more frequently than females in a ratio of about 2.5 to 3:1.⁴ Although lipomas may develop in any organ throughout the body, only 13% occur in the head and neck area.⁵ Within the head and neck region, the most common location is the cheek, followed by the tongue, buccal mucosa, lip, and neck. Occurrence on the eyelid is relatively rare.

Lipomas are classified histopathologically into several distinct subtypes depending on the admixture of other types of tissues. These include simple lipoma, spindle cell lipoma, hibernoma, pleomorphic lipoma, angiolipoma, chondroid lipoma, myolipoma, myxolipoma, myelolipoma, fibrolipoma, intramuscular lipoma, and osteolipoma.¹ Among eyelid lipomas, the most common types are simple lipoma and spindle cell lipoma, but other described forms include fibrolipoma, intramuscular lipoma, and osteolipoma.

Simple lipoma is the most common form, accounting for 80% of head and neck lipomas.⁴ They are composed of mature adipocytes and usually occur just under the skin, but occasionally may be deeper. Most are less than 5 cm in size. The most common locations include the upper back, shoulders, and abdomen, and in a review of 338 simple lipomas, 17% occurred in the head and neck.⁴ The male to female ratio is about 2.5:1. Occurrence in the eyelid is very rare and only two cases of simple lipoma have been reported in this location.⁶,⁷

Spindle cell lipomas are rare tumors that were first described by Enzinger and Harvey in 1991,⁸ characterized by an admixture of adipocytes and small uniform spindle cells. They are benign, painless, slowly growing subcutaneous tumors that occur most often on the upper back, shoulders, and posterior neck with a predilection for middle-aged men.⁹ Rare cases have been reported in the orbit,¹⁰,¹¹,¹²,¹³ and one case was reported in the eyelid.¹⁴

Myolipoma of soft tissue was first described in 1991 by Meis and Enzinger¹⁵ as a rare benign neoplasm characterized by the admixture of mature adipocytes and well-differentiated smooth muscle cells. They are seen predominantly in middle-aged to older females in a male to female ratio of 16:1.¹⁶ The most frequently affected sites are the retroperitoneum (47%), pelvis (15%), abdominal wall (12%), and intra-abdominal sites (9%). One case was reported in the eyelid.¹⁷

Fibrolipoma is an extremely rare subtype of lipoma found most commonly in males. They are characterized by the presence of adipose tissue and abundant amounts of fibrous tissues¹⁸,¹⁹,²⁰,²¹,²² and present clinically as a well-circumscribed, firm to soft, asymptomatic, slowly growing subcutaneous mass.¹⁸,²³ Transformation to liposarcoma has been reported in several cases of fibrolipoma.²³ One case was described in the eyelid.²⁴

Angiolipoma consists of an admixture of mature fat and numerous small blood vessels and usually affects adolescent males.²⁵ This variant accounts for 6% to 17% of all lipomas, but is rare in the head and neck. Only two cases have been described involving the eyelids and two in the orbit.²⁶

Osteolipoma is a very rare variant of lipoma.²⁷ It is a type of lipoma that undergoes osseous metaplasia to become an ossifying lipoma or osteolipoma. Only a few cases affecting the head and neck are reported in the literature.²⁸ One case was described involving the upper eyelid as a nodular swelling that gradually increased in size over 5 years.²⁹ It presented as a 2 cm, firm, freely mobile, painless mass with a smooth surface that was initially diagnosed clinically as a dermoid cyst.

An intramuscular lipoma is a subgroup of lipoma usually seen in large muscles of the extremities and which diffusely invades skeletal muscles. They have also been referred to as infiltrating lipoma.³⁰ It is a rare variant that accounts for about 1.8% of all lipomas³¹ and is very rarely reported in the small muscles of the head and neck.³² Charles and Palu³³ reported a case of an unencapsulated intramuscular lipoma within the lower eyelid orbicularis oculi muscle consisting of mature adipocytes traversed with sheets of striated muscle fibers. A second case was described involving the upper eyelid orbicularis muscle by Buller et al.³⁴ Shiraki et al³⁵ reported a case of intramuscular lipoma in the medial rectus muscle of the orbit. The recurrence rate of intramuscular lipoma after treatment is higher than for most other types reported to be 3% to 62.5%,³⁶,³⁷ most likely due to incomplete resection of the involved muscle.

A pleomorphic lipoma is characterized by the presence of spindle cells and bizarre hyperchromatic giant cells. It occurs most often in the neck and upper body of middle-aged to elderly males, but also has been reported in the orbit,³⁸,³⁹,⁴⁰,⁴¹ and the bulbar conjunctiva.³⁸,³⁹,⁴¹ Although it is distinguishable from other variants of lipoma by floret-like cells as a specific histological feature, there is some debate as to the relationships of this tumor.³⁹ Ebrahimi et al⁴² evaluated 146 cases of normal orbital and prolapsed orbital fat and found these cells in 16% and 43% of specimens, respectively. They concluded that floret-like cells may be present in orbital and prolapsed orbital fat as a degenerative process and that what has been called “orbital pleomorphic lipoma” may only be age-related orbital fat.

Nasopalpebral lipoma-coloboma syndrome is an extremely uncommon autosomal dominant craniofacial disorder characterized by upper eyelid and nasopalpebral lipomas, colobomas of upper and lower eyelids, telecanthus, a broad nasal bridge, broad forehead, widow’s peak, flaring of medial eyebrows, telecanthus, and maxillary hypoplasia. Other features can include aplasia of the lacrimal puncta with epiphora, aberrant eyelashes, conjunctival hyperemia, opacities of the cornea and lens, and divergent strabismus. This syndrome was originally described as a familial disorder, but several sporadic cases have been described.⁴³,⁴⁴,⁴⁵,⁴⁶ The condition is usually bilateral, but rarely it can be unilateral.