Subconjunctival fat prolapse and dermolipoma of the orbit: differentiation on CT and MR imaging

Subconjunctival fat prolapse and dermolipoma of the orbit are unfamiliar to radiologists and yet should be differentiated because their treatments are different. The purpose of this study was to investigate the CT and MR imaging findings that distinguish these 2 conditions.

Between 1995 and 2009, we found 33 patients (27 men, 6 women; mean age, 63 years) with surgically proved subconjunctival fat prolapse and 27 patients (3 males, 24 females; mean age, 17 years) with dermolipoma in our hospital. Among them, 8 patients with subconjunctival fat prolapse and 6 patients with dermolipoma underwent CT and/or MR imaging examinations. We retrospectively reviewed CT scans and MR images in these patients.

In all of the 8 patients with subconjunctival fat prolapse, CT and MR images demonstrated the herniated fat at the superotemporal epibulbar area, continuous with the intraconal fat, extending forward between the lateral wall of the globe medially and the lateral rectus muscle and the lacrimal gland laterally, either bilaterally (n = 7) or unilaterally (n = 1). In contrast, all 6 patients with dermolipoma had a unilateral, crescent- (n = 5), or triangle-shaped (n = 1) fatty mass at the temporal or superotemporal epibulbar area, which lay on the lateral wall of the globe, anterior to the insertion of the lateral rectus muscle and medial to the lacrimal gland, without connection to the intraconal fat.

The characteristic CT and MR imaging findings may help easily differentiate subconjunctival fat prolapse and dermolipoma, both of which usually present as an epibulbar fatty mass in the lateral canthal area.