 So let's turn our attention now to tumors. We will talk about both malignant and benign tumors in the parotid submandibular and sublingual gland. This chart will outline what the frequency is of malignant and benign tumors in each of these glands. So in the parotid gland, the vast majority of the tumors we encounter are benign, thankfully. 80% benign within the parotid gland. But when we move to the submandibular gland, it's 50-50. Only about half of them are benign. Once we get to the sublingual and also the minor salivary glands, that ratio has reversed from the parotid and now 80% are malignant and only 20% of these tumors are benign. So what sort of tumors, what sort of histopathology are we encountering when we encounter salivary tumors? Well, in the benign category, there is a long list of tumors. But there are two that I think are really worth knowing the most about, pleomorphic adenomas and worthens tumors. That's why they're highlighted here. There are many others, adenomas, oncocytomas, oncocytic papillary cyst adenomas, and the list goes on and on beyond what I have put here. But the two that are most important are pleomorphic adenoma and worthens tumors. Similarly, on the malignant side, there is a long list, an even longer list of potential malignant tumors. But there are two that I think that are worth focusing on, mucoepidermoid carcinoma and adenoid cystic carcinoma. So we'll talk about those two. We'll mention briefly, carcinoma, x-pleomorphic adenoma, because it's an important concept. But these two are the two most common and the ones worth studying the most. So first, pleomorphic adenoma are most common, benign tumor. It has a synonym, benign mixed tumor. It generally affects females over the age of 40, a cluster of grapes appearance. Here is a standard appearance for a pleomorphic adenoma, well-defined, heterogeneous enhancement within the superficial lobe of the parotid. Here's a much larger tumor, and you might wonder, how do we know this is a pleomorphic adenoma? Well, it's difficult to be certain. This tumor is bright on T2, but not brighter than CSF. So it's not super bright, not that specific sign. But this gap right here, in between the mandible and the styloid process, the stylo-mandibular tunnel. This tumor is extending through the stylo-mandibular tunnel, and that is a good clue that you are dealing with a pleomorphic adenoma. It is a clue, it's not absolute, but it is a clue. Here's another example of a mass extending through that stylo-mandibular tunnel. Though most of the mass is in the deep lobe, it is extending through that stylo-mandibular tunnel. Now this lesion is so bright on T2, it is in fact brighter than the CSF. This is almost certainly a pleomorphic adenoma because of its benign appearance, that extension through the tunnel, and in particular, that bright T2 signal. Here's what it looks like when it recurs. When a pleomorphic adenoma recurs, there are innumerable, tiny foci everywhere of recurrent tumor, and those are those little tendrils of tumor that were not completely resected. So let's turn our attention to Wharton's tumor. Wharton's tumor also has some synonyms, adenolymphoma, papillary cyst adenoma, lymphomatosome. Wharton's tumor is famous for being multifocal. We think of the, is it being multifocal? But in fact, only 15% of Wharton's tumors are multifocal. They may be bilateral, they may be multiple in the same gland, but only 15%. It's famous for that because not much else is multifocal, but in fact, it's a minority of these tumors. Wharton's tumor undergoes cystic degeneration, and it can be detected using protectantate scans, although we don't often use those for that purpose. Here's a characteristic appearance of a Wharton's tumor. It does not enhance it as a cystic appearance centrally, but again, a very well-defined tumor. Here is an example on MRI. This, because these are cystic, they have a possibility of becoming super infected, as in this case, you can see all the surrounding inflammation. Now, this is an example of a multifocal tumor. Again, it's a minority of cases that end up being multifocal, but this patient had multiple examples of Wharton's tumor within a single gland. Onto the malignancies. Mucoepidermoid carcinoma is the most common alignancy to affect the parotid gland. Although adenoid cystic is more common in the smaller glands, the parotid gland, most commonly mucoepidermoid carcinoma. It comes in two forms. There is a high-grade form and a low-grade form. And the prognosis of the tumor is related to that grade. It's 30% five-year survival for a high-grade tumor, but 90% five-year survival for a low-grade tumor. You can tell these apart radiologically by how infiltrative the tumor is. An infiltrative, aggressive appearing tumor is a high-grade tumor, but a well-circumstribe tumor is a low-grade tumor. There is a high risk of metastatic disease from mucoepidermoid carcinoma, such that routinely a neck dissection will be performed, even if there is no radiologic or clinical evidence of a metastatic disease. These can undergo cystic degeneration and calcification, although it is uncommon. And they characteristically have a low T1 signal and a variable T2 signal, depending on the grade. The lower the T2 signal, the higher the grade of the tumor. So here's an example of a well-defined mucoepidermoid carcinoma. And this is likely to be a low-grade tumor. Here's another example on MRI, very well-defined, uniformly enhancing, a low-grade mucoepidermoid carcinoma. Here's an example of a very aggressive tumor with infiltrative disease, all through the gland, deep lobe, superficial lobe. This is what a high-grade mucoepidermoid carcinoma characteristically looks like. Let's look at another histopathology, the adenoid cystic carcinoma. Adenoid cystic carcinoma is famous for its propensity to perineural invasion, and rightly so, it really has a strong propensity to that. Lymphoma is the other disease that tends to do that. Unfortunately, adenoid cystic carcinoma is essentially incurable. However, these tumors can undergo a very prolonged remission, and patients who get local regional control may go for 10, 20 years, far longer than most of the tumors that we treat, without evidence of recurrent disease. When this disease does recur, it tends to be as distant lung metastases. So here's a characteristic example of an adenoid cystic carcinoma, very infiltrative, very angry appearance. I want to particularly note this spread medially along a nerve called the auricular temporal nerve. The auricular temporal nerve is a branch of the fifth cranial nerve. So the fifth cranial nerve comes down through Fraymino Valley and comes across the infertemporal fossa. As it's doing that, V3 is headed towards the mandible. It gives off a very important branch, the auricular temporal nerve. That branch comes laterally behind the mandible, behind the neck of the condyle, and then enters the parotid gland and feeds the skin overlying the parotid gland. Now we like to think that perineural spread of tumor comes along the facial nerve. So we like to think of perineural spread as coming along the facial nerve. But an alternate way of perineural spread for an adenoid cystic carcinoma of the parotid gland is to instead come medially along the auricular temporal nerve and then crawl up along V3 into Meckles Cave. So that is an alternate way for adenoid cystic carcinoma or other tumors of the parotid gland to reach the intracranial vault. And so here's an example of that perineural spread, where we've gone from the auricular temporal nerve into V3 up through the perineural valley, and there is even a nodular enhancement within Meckles Cave indicating spread of disease. I want to show another example of perineural spread from an adenoid cystic carcinoma, this time along V2 through perineural valley. You can really see it along its length on these axial images. Another example of perineural spread, this time back more classically along the facial nerve, when you see tumor filling up the stylamastoid foramen like that, make sure you check along the course of the facial nerve to see if there's enhancement along that vertical segment or even further along for perineural spread of disease. Yet another example of perineural spread, this time along the branches of the third cranial nerve, coming through the superior orbital foramen and into the orbit. And here's an example of the classic appearance of cannonball metastases throughout the lung, a characteristic way for this tumor to recur often after a long remission. So let's talk about masses that arise within the salivary glands, but are not of salivary origin. Lipomas are very common, and they are an easy diagnosis to make once you recognize them as fat-containing. Hemangiomas are surprisingly common, venous malformations. Hemangiomas are surprisingly common within the parotid gland. They are most easily identified by their brisk enhancement. If you can find phleboliths, that's another great clue. Lymphoma can arise as a primary disease within the parotid gland and usually affects more than one lymph node. Remember that the parotid gland is unique that it has lymph nodes, so lymphoma occurs within only the parotid gland, and it's usually multifocal, multiple nodes within the gland, and that is a good clue to that diagnosis. Metastases can come from anywhere in the body to this area. This happens to be a renal cell carcinoma. You would never have predicted such a thing. Metastasizing to the parotid gland, to a lymph node within the parotid gland. So looking back on salivary tumors, before we move on, a solitary mass is usually going to be a benign or malignant tumor. Plemorphic adenoma is the most common benign tumor. Adenoid cystic carcinoma, the most common malignant tumor, except in the parotid gland where mucoedermoid carcinoma comes out a little bit ahead. Multifocal masses, on the other hand, you have a different differential diagnosis. Think about warthans tumors. Think about lymphomas. Think about metastatic disease for multifocal masses. One of the, unfortunately, it's very difficult for us to distinguish between all of these things. You'll notice that many of the pictures I showed you looked very much alike. It's very hard to distinguish these different diseases. Sometimes a very aggressive tumor, we know it's a malignancy, but often we cannot come up with a specific diagnosis. To make a specific diagnosis, we require tissue sampling.