Retinoblastoma (RB) is the commonest intraocular tumor in children representing approximately 4% of all pediatrics malignancy. [1] It can present as unilateral, bilateral or trilateral disease (bilateral RB tumors and pineoblastoma as a third intracranial tumor). [2]
The former Reese–Ellsworth classification, created in 1960s, was used to predict globe salvage with external beam radiotherapy when this used to be the most popular non-surgical treatment avoiding enucleation. [3] Recommendations were proposed to update this classification to include the current treatment modalities and outcome. [4] The International Classification of Retinoblastoma (ICRB) was introduced and finalized by a group of RB experts in April 2003, which is being used in this study. [5] The main goal of ICRB was being applicable to predict treatment success with current modalities such as chemo-reduction (CRD) therapy. This classification, is based on the number, location and size of RB tumor as well as the presence or absence of vitreous and subretinal seeds and whether they are localized or diffuse. [5]
Management of RB in general is tailored to each individual patient, but several factors play important roles in each case including: metastatic risk, risk for second tumors, systemic condition, laterality, size and location of the tumor(s) and potential for vision. The priority is to detect and treat life-threatening conditions, then to save the globe and finally maintain vision. [1] Current management modalities include: intravenous chemo-reduction, intra-arterial chemotherapy, thermotherapy, cryotherapy, laser photocoagulation, plaque radiotherapy, external beam radiotherapy, and enucleation. [1,3, 6]
Uniform consensus as to what constitutes high-risk pathology has not been reached and high-risk pathological features have been described with few debates in the literature. [7,8,9] However, it has been agreed among many experts that the high-risk features should include: post-laminar optic nerve (ON) invasion, massive choroidal invasion, combined ON and choroidal invasion (of any type) or anterior segment invasion (infiltration of anterior uveal stroma). [9,10,11]
The presence of high-risk histopathological features after primary enucleation is an indication for adjuvant chemotherapy in view of increased risk of metastasis. Survival in these children increased significantly because of adjuvant chemotherapy. [8] On the other hand, secondarily enucleated globes following neoadjuvant chemotherapy did not seem to reduce the chance of harboring high-risk pathological features when compared to primarily enucleated globes. [12] In another study, invasion of the anterior structures (anterior chamber, iris, and ciliary body) was significantly more detected in secondarily enucleated globes with RB. [13]
Based on the international RB staging work group for histopathological studying and globe preparation, ON invasion level has been classified as being prelaminar, laminar (intralaminar), post-laminar and involving surgical margin. Consensus on choroidal invasion has been also reached, where this can be focal or massive (massive choroidal invasion is defined as having diameter of 3 mm or more in any tumor dimension). [14] Magnetic resonance imaging (MRI) is now becoming the most widely used modality in the workup for RB staging and assessment prior to primary enucleation. [15] To detect risk factors for metastasis, MRI is a helpful tool but not as reliable as histopathology, where microscopic infiltration is best detected. [11] Generally, the role of MRI in RB assessment includes: determination of the growth pattern, extension of the ON involvement, detection of orbital and/or meningeal extension, and the presence of second tumors. [16] Additionally, detection of ON invasion on MRI in children treated with primary enucleation might have a role in helping the surgeons to ensure free resection margin. [17]
The aim of this study is to correlate the detected-ON invasion by imaging with the corresponding histopathological level of invasion. The cases where MRI showed more advanced level of ON invasion than what has been detected on histopathology were further subjected to more sectioning either by obtaining deeper levels or by sectioning the globes after rotating the blocks.