Epibulbar Complex Choristoma Containing Bone: A Case Report and Closer Look at Classifications

Abstract

Introduction

Epibulbar choristoma is a benign congenital lesion containing histologically normal-appearing tissue in an abnormal ectopic location. An epibulbar choristoma is classified as either epibulbar dermoid, dermolipoma, or complex choristoma based on histological examination. The case presented was a presumed epibulbar dermolipoma with no signs of ossification on imaging, examination, or intraoperatively until the specimen was examined histologically, clarifying the lesion as an epibulbar complex choristoma. Reassuringly, the presence of bone in such lesions should not change management.

Case Presentation

A mother noticed a small fleshy mass on her 9-year-old daughter’s superotemporal bulbar conjunctiva. The suspected epibulbar dermolipoma was confirmed with MRI and initially managed conservatively. Two years later, she was referred for apparent growth and cosmetic concerns, and she underwent surgical debulking.

Conclusion

We present this case for its unusual presentation and histological findings. Orbital surgeons should be aware of the possibility of ossification of epibulbar choristomas and avoid confusion with alternative diagnoses. Clarification of the latest classification system for epibulbar choristomas is provided.

Introduction

A choristoma is a congenital tissue growth containing histologically normal-appearing tissue in an abnormal ectopic location [1]. The term choristoma is etymologically derived from the Greek term “choristos” (χωριστός), denoting “separated,” suggesting that the tissue has been separated from its typical location [2]. Choristomas can be found within the bulbar conjunctiva and may contain various tissue types. Based on the tissue types contained within, epibulbar choristomas are classified as either epibulbar dermoid, dermolipoma, or complex choristoma [3]. Unlike other reported cases of epibulbar complex choristoma, this case appeared as an otherwise normal epibulbar dermolipoma both clinically and during surgery. However, pathological correlation determined the lesion to be a complex choristoma containing bone.

Case Presentation

A 9-year-old female was initially referred to the senior author (T.G.H.). Her mother was concerned about a fleshy mass appearing on the superotemporal aspect of her left eye (Fig. 1). Her mother explained that she thought the patient often awoke with a “puffy eye,” yet it was not until she lifted the upper lid to check for loose eyelashes that she noticed the mass. Upon examination, a suspected moderate epibulbar dermolipoma was seen in the superotemporal bulbar conjunctiva with no hairs or inflammation. The remaining ocular examination was within normal limits, including bilateral 6/4 vision, normal pupils, normal ocular balance, and full motility with no hemifacial asymmetry or microsomia. An MRI prior to referral showed a high fat signal on T1-weighted imaging and was consistent with a diagnosis of suspected epibulbar dermolipoma (Fig. 2). The patient was initially managed conservatively.

Fig. 1.

Image of the left superotemporal epibulbar complex choristoma.

Fig. 2.

T1-weighted MRI axial (a) and coronal (b) section of orbits showing high fat signal in the superotemporal epibulbar region. There is no extension from orbital fat posteriorly, and the signal is more intense than orbital fat, given that the epibulbar choristoma fat more closely resembles subcutaneous fat.

Two years later, the patient re-presented as it was felt that the mass had grown. It was still not causing any discomfort, with vision remaining 6/4 bilaterally. The lesion, now just visible at rest, appeared to have a small region of conjunctival keratinisation and a small “symblepharon” to the lateral canthus. At this time, it was decided that the patient would be managed with surgical debulking.

Successful surgical debulking was performed under general anaesthesia. Only the keratinised surface epithelium was excised, retaining all non-keratinised conjunctiva. No additional management was required for the small asymptomatic symblepharon. No other abnormalities were noted at the time of surgery, with the excised specimen macroscopically consistent with a typical epibulbar dermolipoma. Subsequent histological examination of the specimen revealed conjunctiva with underlying fibroadipose tissue and a rounded central fibrous nodule with bone containing some dilated thin-walled vessels (Fig. 3). The various heterotopic tissue types identified necessitated that the lesion be named an epibulbar complex choristoma, rather than epibulbar dermolipoma. The patient was followed up 1 week and 3 months later with no complications and a successful cosmetic outcome.

Fig. 3.

Small shell of bone in the fibroadipose tissue. Haematoxylin and eosin. Magnification ×4 (a, b).

Discussion

The mass was suspected to be an epibulbar dermolipoma, defined as a choristoma containing stratified squamous epithelium and adipose tissue typically found in the superotemporal bulbar conjunctiva. The subsequent finding of centrally located bone conflicted with this diagnosis. According to the 5th edition of the WHO Classification of eye and orbital tumours, an epibulbar complex choristoma may contain additional “heterotrophic tissues like bone, cartilage, nerve, and skeletal muscle” [3]. This lesion would thus be regarded as an epibulbar complex choristoma containing bone. Similar lesions in the literature have been referred to as epibulbar dermolipoma containing bone, epibulbar osseous choristoma, or similar [4–7]. In concordance with the latest WHO classification system, epibulbar complex choristoma is the preferred terminology for these lesions.

While the lesion appeared completely typical of an epibulbar dermolipoma, it can be indistinguishable from epibulbar complex choristomas, unless the other tissue that makes it “complex” is clearly visualised clinically or on imaging. We reassure readers that this distinction is largely academic and should not alter management. However, awareness of the possibility of ossification in a lesion otherwise suspected to be epibulbar dermolipoma is important. This may avoid confusion with other differential diagnoses such as metallic foreign body, particularly as an incidental finding on imaging.

The ossification was not apparent on imaging, clinical examination, or intraoperatively. This is in contrast to similar reported cases which had more apparent bone being detected through such methods [4–7]. The initial MRI 2 years prior to re-presentation and debulking showed typical epibulbar dermolipoma morphology with a high T1-weighted fat signal similar to that of subcutaneous fat, rather than orbital fat (Fig. 2a). Yet, the MRI failed to demonstrate any signs of ossification [8]. A possible explanation is the very small thin nature of the focus of bone present (Fig. 3). If specifically assessing for bone, black bone MRI sequence or CT scan may be preferable [9].

As is previously reported, this case also illustrates that it is safe to manage epibulbar choristomas conservatively until they are problematic by causing ocular surface symptoms or cosmetic disfigurement. When indicated, a subtotal excision is recommended to minimise complications from excessive tissue removal [10, 11]. The sole presence of bone within an epibulbar choristoma should not change management.

Epibulbar choristomas are most often sporadic but can be commonly associated with Goldenhar syndrome or craniofacial microsomia, hence the importance of checking for other features including facial asymmetry and signs of incomplete development around the nose, soft palate, mandible, and ear on the ipsilateral side [12]. The patient did not exhibit signs of any other syndromes associated with epibulbar choristoma (Duane retraction syndrome, nevus sebaceous syndrome, encephalocraniocutaneous lipomatosis), suggesting that the lesion was likely sporadic [13–15].

We describe a case of epibulbar complex choristoma with the unusual histological finding of ossification and provide clarification around the classification of epibulbar choristomas. We also reassure readers that ossification should not alter the management of such lesions. The CARE Checklist has been completed by the authors of this case report, attached as online supplementary material (for all online suppl. material, see https://doi.org/10.1159/000538824).

Statement of Ethics

Ethical approval is not required for this study in accordance with local guidelines. Written informed consent was obtained from the parent of the patient for publication of the details of their medical case and any accompanying images.

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Funding Sources

The study was not supported by any sponsor or founder.

Author Contributions

Z.G.A. wrote the manuscript. T.G.H. identified the case and supervised the project. P.M. provided expertise and guidance around classification of the lesion.

Funding Statement

The study was not supported by any sponsor or founder.

Data Availability Statement

All data generated or analysed during this study are included in this article. Further enquiries can be directed to the corresponding author.