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Interpreting a Pituitary MRI
Sellar Anatomy, Imaging Indications, and Different ...
Sellar Anatomy, Imaging Indications, and Differential Diagnosis
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Video Transcription
So here, this is what I'm going to be talking about briefly. So just brief overview of the cellar anatomy, talk about indications for cellar imaging, imaging protocols, what the normal pituitary looks like on MRI, and then review, present an overview of the differential diagnosis of cellar masses, and then I'll share with you some of our cases, and hope to convince you that the radiographic features of a cellar mass can help you arrive at a presumptive diagnosis preoperatively in many cases. So here's what the cellar looks like on a coronal section. You're familiar with it, but just to review briefly with you, you see the pituitary, the into the hypothalamus, the optic chiasm in the supercellar cistern, and then bounded laterally by the cavernous sinuses that contain important structures, the carotid artery, and then the third, fourth, sixth, and the first two branches of the fifth nerve. Of course, the sphenoid sinus shown inferiorly here with the septations, and these are important both clinically, radiographically as well. Cellar lesions can impinge upon some of these structures. And of course, optic nerve compression can lead to a variety of visual field effects, as you know, classically by temporal vision field loss. But also, lateral extension can compress these nerves that are in the cavernous sinus, leading to, for example, oculomotor or other nerve pulses. And these are typically seen in lesions other than pituitary adenomas. Unless they bleed, will very rarely lead to dysfunction of these nerves in the cavernous sinus. And this is actually very helpful clinically. So again, when should you be thinking about imaging the pituitary, first of all? Well, one situation is mass effect on paracellar structures. Already touched upon this, that cranial nerve dysfunction involving the second, third, fourth, fifth, or sixth cranial nerve is a situation when you want to think about imaging the cellar. Severe headache, particularly if acute onset and associated with cranial nerve dysfunction that raises the possibility of apoplexy, bleeding into a cellar mass. And then evidence of pituitary hormone excess or hypopituitarism. So it's very important for everyone to consider that when imaging of the cellar is requested, one should specifically ask the radiologist for a pituitary protocol MRI, not just any MRI. Because on a regular MRI, you'll be lucky if you'll get a sagittal view of the cellar, which is non-magnified. But you're not going to get focused views of the cellar. So if you ask in our center and in many hospitals, radiologists have agreed on what a pituitary protocol MRI should be. So when you actually wish to image the cellar, you need to specifically request one. So a pituitary protocol MRI should include, at the minimum, coronal and sagittal T1-weighted views of the cellar that are high resolution with a large field of view to encompass the cellar. And also thin slices, 2 to 3 millimeter thin slices, so that adequate views of the cellar can be obtained. And these should be obtained both before and after gadolinium administration. In addition, these are usually supplemented by coronal T2-weighted sequences, which can be very helpful to detect particularly cystic fluid or blood. And I'll show you some of these examples. Now, even though the focus is the cellar, it's very helpful many times to look at the rest of the brain, because there are some cellar pathologies that can involve other brain areas. And I'll show you some examples. OK. So what about a CAT scan? A pituitary protocol CAT scan can be helpful and, in fact, can be the only option in some patients who have pacemakers, especially older pacemakers that are not compatible with use of MRI imaging. In addition, there are some situations when a CAT scan can be advantageous to MRI, specifically looking at bone erosions, large tumors that erode the clivus or the sphenoid. You can look at the bone more closely with a CAT scan. You can look at patients of cellar calcifications, which can be seen, for example, in patients with craniopharyngiomas, among other tumors that can be appreciated much better with a CAT scan as opposed to an MRI. Or very acute hemorrhage within the cell is more obvious on a CAT scan. So what does the normal pituitary look like on MRI? This is a sagittal view. And this is a T1-weighted sequence that you see. It's obtained before contrast administration. So you can see, of course, the anterior pituitary here in this image, which is isointense to white matter on T1-weighted images. And I think it's important for you to remember that the anterior pituitary enhances after gadolinium. And this is in contrast to most of the rest of the brain, where enhancement is usually is always abnormal, indicating breakdown of the blood-brain barrier. But because the pituitary and the stock is outside the blood-brain barrier, enhancement is actually physiologic. Now, the posterior pituitary, as you see on this image, is actually brighter than white matter on T1-weighted images. And this is because it is thought that the presence of the neurosecretory granules in the axons that come from the hypothalamus, and these granules contain ADH and oxytocin, these give rise to this bright signal. And this is also important clinically, because patients, the vast majority of patients with postnatal diabetes insipidus will lack this bright signal on MRI. The shape of the pituitary, as you can see, tends to be flat or concave, a superior border. In adolescents, young adults, one may see an upward convexity. Also early postpartum, convex superior shape of the pituitary is common as a result of lactotroph hyperplasia, which is physiologic during pregnancy. So what about the dimensions? You can see that the normal pituitary measured on the sagittal plane, the height is up to 8 millimeters in men or 10 millimeters in women, again, somewhat greater early postpartum. And also, one should pay attention to the stock. As you can see, a stock dimension, a diameter above 4 millimeters is considered generally abnormal. One can see fine cellar masses during evaluation, either of mass effect or hypopituitarism or evidence of hormone excess. But also, they can be incidental findings, in fact, not uncommon. The data from Dr. Freda, in which the vast majority, at least in the surgical series, but also among incidentally found lesions, the vast majority of the lesions in the cell are pituitary adenomas, at least 90%. And in that series, in this particular series I show here from New York, about 40% were clinically non-functioning pituitary adenomas, which are generally of gonadotroph lineage. Notice that prolactinomas are underrepresented here because most of them are treated medically. And then you see the usual breakdown between growth hormone, corticotropin secreting, and thyrotropinomas, which are, of course, the least common of them. But in addition to the pituitary adenomas, there is the other 8% to 9% of cellar masses. They come in a wide variety of lesions. You can see that there are both benign tumors, such as craniopharyngiomas or meningiomas, as well as malignant tumors, germ cell tumors, gliomas, and a variety of others. Cystic lesions, rathies, cleft cysts, arachnoid cysts, and others, vascular lesions, and empty cellar. There is a variety of inflammatory lesions, both primary hypophysitis or systemic hypophysitis as a result, for example, of sarcoidosis or Langerhans cell histiocytosis. In addition, very occasionally, one can see infection in the cellar, bacterial, tuberculous, fungal, and others, more rarely. About the occurrence of pituitary hyperplasia, lactotrophic hyperplasia is, of course, physiologic during pregnancy, but also severe target gland hypofunction may lead to hyperplasia and familiar example is patients with very severe untreated primary hypothyroidism sometimes present with a large cellar mass representing thyroid hyperplasia, and this is actually reversible upon institution of thyroid hormone replacement. So this is important to recognize clinically to avoid unnecessary surgery. So there's a wide differential diagnosis, and I'm just going to share with you some cases to hopefully convince you that reviewing the imaging features of cases can actually help arrive at the presumptive diagnosis preoperatively. These are patients who did not have pituitary adenomas, and they were operated over a 10-year period. And you can see among the non-adenomatous lesions, cystic lesions are most common, followed by benign tumors. Malignant tumors are an important category, slightly less common in this series. And then inflammatory lesions, only 9%, but inflammatory lesions are often treated medically, so this is probably underrepresented somewhat.
Video Summary
The video discusses various aspects of cellar anatomy and the importance of imaging in diagnosing cellar masses. The speaker explains the indications for imaging, the protocols involved in a pituitary protocol MRI, and the radiographic features of a normal pituitary on MRI. The video also delves into the differential diagnosis of cellar masses, including benign and malignant tumors, cystic lesions, inflammatory lesions, and vascular lesions. The speaker presents cases to showcase how reviewing imaging features can help reach a presumptive diagnosis before surgery. No credits are mentioned in the video. Overall, the video emphasizes the importance of proper imaging techniques for accurate diagnosis of cellar masses. (138 words)
Keywords
cellar anatomy
imaging
diagnosing cellar masses
pituitary protocol MRI
differential diagnosis
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