 Thankfully, in the orbit, benign masses are much more common than malignant masses. So the most common of these common benign masses is the venous malformation or hemangioma. Varices of the veins within the orbit are also very common, and then we get into the less common things, dermoids, neurofibromas, and then we'll talk for a little while about gliomas and meningiomas around the optic nerve and how we can distinguish those two lesions. So this heterogeneous lobular enhancement that we're seeing within this lesion is the characteristic finding of a venous malformation, a lobular enhancing lesion, very characteristic of this disease have a high level of suspicion for this diagnosis because it is the most common benign mass, the most common mass to arise within the orbit. When you see a mass that has a laminar appearance on T1 and T2, it looks like there's different content centrally than at the periphery of this mass. This is when you should start to think about a venous varix. Notice the bright T1 signal, that's not enhancement, that's intrinsically bright T1 signal because it is a partially thrombosed venous varix within the orbit. Sometimes these will appear even as bilateral masses, as in this case bilateral venous varices. If you see something, if you see a mass in the orbit that looks just like a lipoma, don't call it a lipoma. It is probably not a lipoma, it is probably an orbital dermoid. These look just like lipomas, they are filled with fat. They do not look like lipomas clinically because unlike a soft lipoma these are hard. So it's very easy to distinguish the lipoma from the dermoid clinically, they look the same radiologically. In this location it's much more likely to be a dermoid than it is to be a lipoma. Plexiform neurofibromas, classically in the setting of NF1, will affect the orbit and you can see them crawling along the expected course of the third cranial nerve here, expanding the superior orbital fissure like so. An expanded superior orbital fissure in this setting, classic for Plexiform neurofibroma. Remember that in some cases of neurofibromatosis you get extensive dysplasia of the sphenoid bone as a result of these surrounding neurofibromas. So let's talk about the difference between gliomas and meningiomas. These are both masses that occur within the intracornal space along the optic nerve, but the glioma is a central mass that replaces the nerve, it is an expansion of the nerve itself. Whereas a meningioma is arising from that peripheral nerve sheath, so it is a mass around the nerve, not a mass of the nerve. That results in a classic imaging appearance of tram tracks, which I will show you. So here's a lesion that is running right along the expected course of the optic nerve. When we see it in coronal image, we see it is uniformly enhancing and it is a mass of the nerve itself. There is no preserved central nerve, this is the nerve expanding and enlarging. This is what an optic nerve glioma looks like. That's that with this image here. Here there is a preserved dark nerve centrally and the enhancement is all around peripherally around the nerve and somewhat poorly defined. This is characteristic of an optic nerve sheath meningioma. It's arising around the nerve, sometimes it can crush the nerve quite a bit, but it is arising around the nerve, not in the nerve. Now let's look at this in axial image and we can see again the preserved nerve down the center and the enhancing tumor on either side. Characteristics of a meningioma and this is the tram track that we are talking about. The two lines parallel to one another tram track, classic tram track appearance of an optic nerve sheath meningioma. So those are benign masses. Let's turn now to malignant masses. The most common malignancy to arise in the orbit is lymphoma, but we also encounter minor salivary tumors, particularly arising from the lacrimal gland, which as we all know, is a modified salivary gland and all of those diseases that we talked about in the salivary glands earlier today can arise within the lacrimal gland. You can get rhabdomyo sarcomas arising within the orbit and metastases of any sort can affect the orbit, but breast is famous for it and it appears in a very particular radiologic appearance which I will show you. So first lymphoma, a uniformly enhancing mass. Notice how polite this lymphoma is with respect to the globe itself. It's sort of conforming around the globe. It's just, it's working its way around the globe. It's not eating the globe. It's not, it has a very benign appearance overall. But it is a malignancy lymphoma when it arises in this location. It's usually polite like this and it does not erode surrounding structures. Still be suspicious in this circumstance. This picture I've shown you before, it's adenoid cystic carcinoma arising within a lacrimal gland and extending along the branches of the third cranial nerve. Adenoid cystic carcinoma of course famous for perineural spread. How about these, this lesion, this is a huge lesion. It is centered however not within the orbit itself but within this triangle of bone behind the orbit. This is the sphenoid buttress and this is a bone lesion that is secondarily involving the orbit, temporalis fossa and the middle cranial fossa. It's expanding in all directions out from this bone and if you look carefully you'll see that it has a counterpart somewhat smaller on the other side. This is metastatic disease, this happens to be breast cancer. But metastatic disease from any source to bone could do something like this. Now this is a very interesting appearance. Notice in this case that there is abnormal enhancing tissue that completely fills the normal fat spaces of the orbit. This should all be filled with fat, orbital fat. Instead it is filled with enhancing soft tissue. And yet, instead of the proptosis that you would expect, expanding the globe out from the eye, instead the globe has been retracted back. This patient has enopthalmos, not proptosis. So how can you have an infiltrative mass that causes negative mass effect that pulls back on the eye? This is a classic appearance of scurus breast cancer metastases. Breast cancer is unique in doing this and with retracting the globe back as it fills the orbit with tumor. Here's the same thing on an MRI. You can see that the normal, bright fat of the orbit has been all replaced by this tumor. And the globes have been retracted back enopthalmos from metastatic disease. Classic scurus breast cancer.