Main

Sir,

Lipomas are common, benign tumours composed of mature adipose tissue. The majority are located subcutaneously around the torso, neck, and proximal limbs.1 Intramuscular lipoma is a curious subgroup located within muscles, which can invade locally in a diffusely infiltrative pattern.

Intramuscular lipomas of the small muscles of the head and neck are reported only rarely. One previous report has identified intramuscular lipoma involving an eyelid,2 and one recent report describes an intramuscular lipoma within a medial rectus muscle.3 We describe a further case of an intramuscular lipoma affecting an eyelid.

Case report

A 77-year-old man presented with a left upper eyelid mass that had slowly enlarged since first being noticed 3 years previously (Figure 1). He had no pain, diplopia, or impaired vision on that side. On examination the mass was subcutaneous, soft, fatty, and nontender to palpation, and there was no proptosis or globe deviation.

Figure 1
figure 1

Frontal (a) and lateral (b) views preoperatively showing a left upper eyelid mass.

The mass was biopsied under local anaesthesia without complication. During the procedure, it was noted that the lesion extended deep in to the orbital septum adjacent to the medial orbital wall.

The histological examination of the specimen (Figure 2) revealed lobulated groups of mature adipocytes surrounding groups of skeletal muscle fibres and individual muscle fibres, providing the diagnosis of an intramuscular lipoma. The presence of muscle fibres within this lesion refutes the diagnoses of orbital fat prolapse or classical lipoma.

Figure 2
figure 2

Histopathology image from this patient. Note the groups of mature adipocytes surrounding groups of skeletal muscle fibres and individual muscle fibres. Haematoxylin and eosin stain, original magnification × 60.

At follow up 3 months postoperatively, the cosmetic appearance of the eyelid is very satisfactory. There is no residual mass, and the patient is asymptomatic.

Comment

Intramuscular lipomas account for 1.8% of lipomatous tumours and are the most common in middle-to-late adult life.4 They are most commonly found within the large muscles of the trunk and limbs, and if left untreated can become greater than 20 cm in diameter. Morphologically they vary from well-circumscribed lesions to tumours with a highly infiltrative border.4 Owing to their deep location and ill-defined borders intramuscular lipomas may be confused clinically with liposarcomas.

Reports of specific clinical problems caused by intramuscular lipomas include voice and breathing problems from infiltrating tumour of the larynx,5 intussusception of the colon,6 and infiltration of the paraspinal muscles.7

The radiological appearance of intramuscular lipomas varies considerably due to the wide spectrum of tumour morphology: from a single homogeneous mass to a large inhomogeneous lesion with infiltrative margins.8 Muscle bundles within the tumours can occur with both well-circumscribed and infiltrating lipomas. Interestingly, intermingled muscle fibres and an infiltrative margin do not indicate malignancy.

Typically, the fat and muscle tissue within an intramuscular lipoma have an identical intensity to normal fat and muscle tissue on T1- and T2-weighted MRI images, and gadolinium-DTPA does not enhance the lesion.3 Liposarcomas are more likely to be multinodular, with variation of signal intensity between T1- and T2-weighted images compared to normal fat and muscle tissues, and exhibit gadolinium-DTPA enhancement.8

Following surgical excision, reported recurrence rates of infiltrating intramuscular lipomas vary from 19 to 62.5%.4, 9, 10 One study9 with an average 7-year follow-up reported recurrence in five of the 12 lower limb tumours (42%).

Histologically, intramuscular lipomas are composed of mature fat cells, adipocytes, with varying amounts of skeletal muscle fibre bundles contained within the tumour. The histological hallmark of liposarcoma is the lipoblast, or immature fat cell.1 Features that help to distinguish a liposarcoma from benign lipoma are the presence of lipoblasts, myxoid differentiation, cellular pleomorphism, plexiform vascularity, and mitotic activity.

The most common genetic abnormality for all lipomatous neoplasms is translocation between the long arm of chromosome 12 and other chromosomes, particularly chromosome 3.1, 11, 12 Rearrangement of chromosome 12 at bands q13–15 constitutes 64% of lipomas with identified clonal abnormalities. One study identified chromosome 12 abnormalities in seven out of the eight (88%) intramuscular lipomas tested.11

This case reinforces intramuscular lipoma as a differential diagnosis of eyelid masses, and highlights the problems managing a benign, slowly infiltrative tumour in a location where extensive resection is difficult to achieve due to the highly specialised nature of surrounding structures.