A few days ago, I was privileged to attend a workshop of the Retinoblastoma Network (Rb-NET), hosted by LV Prasad Eye Institute, coordinated by the International Centre for Eye Health and funded by the Queen Elizabeth Diamond Jubilee Trust.
During the workshop, clinical workers from several institutions from Indonesia, Kenya, Malawi, Tanzania and Uganda as well as partnered organisations from India and the UK met to discuss how to improve retinoblastoma care.
The attendees included pathologists from several departments, and we had several discussions on current practice and possible developments in retinoblastoma reporting. As part of the outcome of those discussions, I’m going to run a few posts on retinoblastoma histology. I hope that these will serve as a guide as well as a starting point for future discussion.
For this post, I’ll concentrate on anterior segment involvement – specifically, angle involvement.
Normal angle histology
This first image is of a normal iris-corneal angle. The field includes some posterior cornea, trabecular meshwork, Schlemm’s canal, iris, and the very anterior part of the ciliary body.
Here’s the same image with a few annotations:
1. Schlemm’s canal
2. Posterior extent of Descemet’s membrane
3. Ciliary muscle
The yellow highlight covers the trabecular meshwork
The green highlight demonstrates the normal undulating contours of the anterior iris surface. The anterior extent of the iris is bare stroma, with no epithelial covering. In contrast, the posterior (pigmented) extent of the iris is formed of pigment epithelium.
Here’s another normal angle. This patient is of Middle Eastern origin. Note the increased numbers of melanocytes. The anterior iris surface is still undulating.
Retinoblastoma in anterior segment
This first low power view shows tumour within the anterior chamber, coating the posterior corneal surface, on the anterior iris surface, within the iris stroma and within the posterior segment (anterior vitreous)
On higher power, tumour can be seen within the trabecular meshwork, and extensively coating the posterior corneal surface and also just anterior to Descemet’s membrane.
The opposite iris leaflet has tumour on its surface and within the stroma. The normal undulating profile is flattened. This isn’t solely due to tumour, but to a fibrovascular membrane which is also causing angle closure. This is iris rubeosis.
My next retinoblastoma post will examine the optic nerve. Please let me know if there are specific questions you’d like me to address.