Orbital dermoid cysts are cystic lesions classified as choristomas, resulting from incomplete migration of the ectodermal epithelium to the body surface during embryonic development, leaving the epithelium trapped within the mesoderm. These cysts are composed of a cyst wall and cystic contents. The cyst wall is lined by stratified squamous epithelium containing hair follicles and sebaceous glands, while the cyst cavity contains desquamated epithelium, hair, and secretions from sebaceous and sweat glands. The external part of the cyst wall is typically surrounded by fibrous connective tissue.
Clinical Manifestations
Dermoid cysts exhibit slow growth and, although of embryonic origin, are often not identified until childhood or even adulthood. Clinically, they may present with progressive proptosis, ocular misalignment, or vision deterioration. These cysts are frequently located near the superior orbital rim or the superotemporal orbit, causing the globe to protrude and displace downward or inferomedially. Cysts palpable along the orbital rim tend to be of medium firmness with a smooth surface. Those beneath the periosteum are typically immobile on palpation, whereas cysts located on the periosteal surface or within the intraconal space, connected to the orbital wall by a stalk, may exhibit mobility on palpation. Cysts are non-tender unless complicated by inflammation. Ruptured cysts spilling their contents might induce recurrent inflammatory reactions resembling orbital cellulitis. In cases of cyst rupture, sinus tract formation might occur.
Figure 1 Left orbital dermoid cyst
A. External appearance of the patient showing a superotemporal orbital mass in the left eye.
B. CT imaging demonstrates a well-defined, oval-shaped lesion in the subcutaneous tissue of the lateral orbit.
For deeply situated cysts, orbital palpation might be negative, but varying degrees of proptosis and globe displacement can be present. Imaging studies reveal characteristic findings. B-mode ultrasound typically shows a lesion with sharp borders, potentially irregular in shape, with good acoustic transmission. Depending on the cystic contents, the lesion may present as anechoic, moderately echogenic, hyperechoic, or massive echoes, all demonstrating compressibility. X-ray imaging often reveals pressure erosion of the orbital wall, appearing as bone resorption with reduced density and sclerotic changes of surrounding bone, referred to as a "sclerotic ring." CT scans frequently show bony changes and evidence of soft tissue mass effect, with the cyst demonstrating well-defined borders and inhomogeneous density due to the presence of fatty content, usually leading to negative CT values. Bone compression patterns are diverse, and in some cases, the lesion may extend into the orbit, temporal fossa, or cranial cavity, presenting a doughnut configuration. MRI scans demonstrate lesions with hyperintense signals on both T1- and T2-weighted images, though signal heterogeneity may be observed due to variations in cyst contents.
Treatment
Surgical intervention is the treatment of choice. Complete excision of the cyst wall is emphasized during surgery. For regions where the cyst wall adheres to bony depressions and is difficult to remove, phenol cauterization followed by ethanol neutralization and saline irrigation may be employed. Care must be taken when using caustic agents to avoid damage to normal orbital structures.