Orbital masses may be benign or malignant. The patient’s age and location of the lesion helps to narrow the differential diagnosis. Additionally, orbital masses may be classified as primary, secondary or metastatic. Ophthalmologists rely on clinical exam including dilated fundoscopy and clinic-based investigations including optical coherence tomography and B-scan ultrasound.
High resolution imaging is essential to delineate the extent of disease, as this cannot be directly visualized with fundoscopy, such as retrobulbar involvement, perineural invasion, bony erosion and metastases.
Orbital imaging is important in surgical planning to determine the lesion location and the nature of its pathology1. Important features to be considered in orbital mass characterisation are contour (smooth versus irregular or poorly-defined), effect on surrounding tissues (e.g. inflammation, bony erosion), intrinsic characteristics of the lesion such as cystic change or calcification, and dynamic changes such as flow characteristic and expansion with Valsalva1,2,3.
“Traditional” orbital anatomy can be divided into globe, intraconal, extraconal, subperiosteal and the extraocular muscle cone itself1,4
In addition, it is useful for the orbital surgeon to know whether the lesion is
- Anterior, mid-orbit or apical; and
- From which quadrant or surgical space it arises – inferior, medial/superomedial, superior, lateral/superolateral1(note that these overlap)
This approach helps identify the pathology pre-operatively and assists with choice of surgical approach (Fig. 1).
Fig. 1: Surgical approaches to regions of the orbit and examples of conditions encountered(1,4)
Baseline CT imaging is valuable, and a non-invasive ultrasound of the orbit provides significant diagnostic information in posterior chamber pathologies, particularly when the posterior chamber cannot be directly visualised by an ophthalmologist due to an opaque lens or vitreous. MRI is a key imaging modality and valuable in making critical surgical decisions like vision-preserving surgery or orbital exenteration. Imaging is also used in the preparation of custom-made prosthetics and intraoperative navigation.