How to read a 4D parathyroid CT

In this video, Dr. Katie Bailey describes how to review a 4D parathyroid CT for the presence of a parathyroid adenoma. We cover the features of a multiphase, or 4D, CT of the neck and the imaging characteristics which are typical of parathyroid adenomas.

What is 4D parathyroid CT?

It is a multiphase contrast CT, so you have three dimensions in space, and the 4^th dimension is time. It is often done to evaluate for the possible presence of abnormal parathyroid glands or a parathyroid adenoma. There are usually 4 parathyroid glands along the posterior margin of the gland.

How to find a parathyroid adenoma

If looking for a parathyroid adenoma, you should be looking for a round or oval nodule along the posterior margins of the thyroid. A good way to differentiate between a lymph node and a parathyroid is that the vessel often goes to the pole of a parathyroid but to a hilum of a lymph node. If you don’t find one in the expected location, you can check more distant places in the deep neck.

Appearance of parathyroid adenoma

On a noncontrast image, the nodule should be lower in density than the normal thyroid, which contains more iodine.

On arterial phase imaging, a parathyroid adenoma enhances more than the adjacent thyroid.

On venous phase imaging, the adenoma enhances less than the adjacent thyroid because the contrast washes out faster.

Practice case 1

In this practice case, you can see a nodule along the left inferior tracheoesophageal groove. It enhances avidly on the arterial image and washes out on the more venous phase. The sestamibi scan confirms the finding.

Practice case 2

This case shows a normal thyroid which is displaced anteriorly on the left. There is a heterogenous nodule along the posterior margin and extending along the esophagus. The greater heterogeneity of this lesion is caused by hemorrhage

Summary

4D CT is a focused tool to look for parathyroid adenomas in the setting of a clinically suspected adenoma, usually characterized by hypercalcemia. You can use it in conjunction with clinical features, nuclear medicine

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Neck Imaging Reporting and Data System (NI-RADS) Introduction

In this video, Dr. Katie Bailey walks us through an overview of the Neck Imaging Reporting and Data System (NI-RADS) system, including why it was created and a basic overview of the principles and categorization. You can learn more about the American College of Radiology (ACR) NI-RADS system from the ACR website. In this talk, we will walk through some NI-RADS categories, show examples of each, and go through a practice case.

Introduction

NI-RADS was designed to standardize surveillance and follow-up recommendations for tumors of the head/neck and aerodigestive track, including the oral cavity, nasal cavidy, nasopharynx, oropharynx, hypopharynx, and larynx. Most of these are squamous cell cancers but some, such as salivary gland, orbital, and sinonasal tumors are also included.

NI-RADS categories

NI-RADS categories include the primary tumor site and neck to look for recurrence. There are categories from 0-4 depending on the level of suspicion. Each category has a recommended management decision associated with it. Some of the categories are split into subcategories.

NI-RADS 1

Category 1 includes includes expected post-surgical changes and nothing concerning or masslike. Sometimes you can have linear enhancement or mucosal edema, but you definitely don’t have nodular or masslike disease. If you have PET, there will be minimal or no uptake. These patients can have expected follow-up.

NI-RADS 2a

In category 2a, there can be come focal mucosal enhancement, but it would be unlikely to be masslike. If there is FDG-PET, it would be mild to moderate uptake only. These patients may need direct inspection by scope.

NI-RADS 2b

Category 2b may have some ill-defined enhancement in the deep soft tissues. This distinction is important because any abnormal soft tissue may not be visible along the mucosa, so scoping will not be useful. These patients likely need a short-term follow-up.

NI-RADS 3

NI-RADS 3 has a new or enlarging primary mass or lymph node. These tend to be nodular or masslike and probably have intense focal uptake on PET. These patients probably need a biopsy.

NI-RADS 4

Category 4 is for pathologically proven or definite radiologic and/or clinical progression. Because this is definitive progression, these patients need new clinical management or treatment. On follow-up imaging, you may find new disease in a new or distant location. This would be described separately.

Practice case

This practice case is a maxillary sinus squamous cell carcinoma. The initial tumor is very extensive. The first posttreatment scan shows postsurgical changes, with a very small area of focal FDG uptake posterior to the flap. The MRI is very reassuring with no masslike or suspicious enhancement. However, because of the deep PET uptake, we’ll call this a 2b so that it gets short term follow-up.

On the short-term follow-up, the area of nodular enhancement seen previously has worsened considerably, and there is a great deal more involvement of the skull base and adjacent structures. The FDG-PET is very highly avid. We will call this a category 4.

Summary

In summary, we show a flow-chart with the NI-RADS categories so you can quickly review. Hopefully this helps your review of post-treatment head and neck cases go more smoothly.

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Salivary Glands

In this video, Dr. Bailey gives us an overview of salivary gland lesions, including briefly reviewing the normal anatomy and appearance of the salivary glands, common benign and malignant neoplasms, and other infectious, inflammatory, and systemic processes that may affect the salivary glands.

Salivary gland overview

There are three major sets of salivary glands, the parotid, submandibular, and sublingual glands. There are also minor salivary rests elsewhere. The parotid gland is the largest salivary gland, and drains through Stinson’s duct which empties near the 2^nd molar. The submandibular and sublingual glands are in the floor of the mouth in the sublingual space.

Benign salivary gland neoplasms

There are a lot of salivary gland neoplasms, most of which are benign. A good tip is that the larger glands are more likely to have benign lesions. Most parotid lesions are benign, while minor glands have a higher percentage of malignant gland. The parotid is the most common location for both benign and malignant lesions.

The most common benign lesions are pleomorphic adenoma (benign mixed tumor) and Warthin tumors. Pleomorphic adenomas are the most common and tend to be homogeneously dense on CT. On MRI, they are relatively homogeneous, hypointense on T1, and VERY hyperintense on T2. They may have a fibrous rim. Warthin tumors are also benign, and are more common in older men. They are often bilateral, and tend to be more heterogeneous and less T2 hyperintense than pleomorphic adenomas. Bilateral tumors are more likely to be Warthin tumors.

Malignant salivary gland neoplasms

Mucoepidermoid carcinomas are the most common parotid malignancy. There is a lot of overlap with the appearance of benign lesions, but the margins tend to be more irregular. They may also have lower signal on T2. When you have malignant salivary gland lesions, you should check specifically for perineural spread, which can occur along the facial nerve up to the geniculate ganglion or along the trigeminal nerve to the foramen ovale.

Adenoid cystic carcinomas are more common in minor salivary glands and are the most common sinonasal salivary tumor. As the grade increases, they tend to be more T2 hypointense. There are also well known for perineural spread.

Parotid metastases are quite common because of intraparotid lymph nodes. Skin cancers and melanoma as well as lymphoma are common causes of metastatic disease. Like the other malignancies, they tend to have very irregular margins.

Inflammatory and other

Sjogren disease is an autoimmune disease of exocrine glands which results in a multinodular appearance of the parotid glands. Patients may have atrophy of the lacrimal glands. These patients have an increased risk of lymphoma.

Lymphoepithelial cysts are multifocal cystic lesions which are most often seen in patients with HIV due to lymphatic obstruction. They appear as bilateral parotid gland cysts.

Sialolithiasis is formation of stones (calculi) in the duct or parenchyma of glands. They are most common in middle age me and in the submandibular gland. This appears as very dense, calcified and well defined lesions either in gland or along the duct.

Sialadenitis is inflammation of the gland which can be caused by infection or inflammatory conditions. Ascending bacteria from the pharynx is the most common, but viruses and immune mediated causes are also possible.

Practice case

This is a relatively well-defined lesion in the superficial aspect of the left parotid gland. It is hyperdense and somewhat homogeneous, but superficial to the gland. If you review further, there is an additional superficial nodule, and this is spread of an adjacent malignancy. So, this case is malignant. An important lesson in evaluating salivary gland lesions is that you often cannot tell the difference between benign and malignant lesions, so biopsy is required.

Summary

Hopefully these cases taught you something about the normal appearance and anatomy of the salivary glands, some common tumors (both benign and malignant), and other conditions affecting the salivary glands. Be sure to check out the other videos on other head and neck topics.

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MRI of the Orbits

In this video, Dr. Bailey reviews the orbit on MRI, with a focus on anatomy and a few of the most common pathologies.

Introduction

In this video, we’ll review the normal anatomy of the orbit and its appearance on MRI.

Orbital contents and normal anatomy

The postseptal orbit includes the intraconal (within the extraocular muscles) contents and extraconal contents. The muscles themselves are a muscular compartment, but it is useful to think of them in the extraconal compartment. There are many things you’ll find in the orbit, including the muscles, the optic nerve, arteries and veins, and fat.

On pre- and post-contrast imaging, you can identify which structures enhance. The optic nerves, for example, should not normally enhance. Lacrimal glands, the extraocular muscles, and sinus mucosa enhance normally.

Optic nerve

The optic nerve can be affected by masses, infection and inflammation, demyelination, and other pathologies. Optic neuritis is inflammation of the nerve, which is usually seen by enhancement in the optic nerve itself. Radiation can cause optic neuropathy, which may even be bilateral. Optic gliomas are tumors that affect the optic nerve and are associated with neurofibromatosis. Optic nerve ischemia can also cause optic neuropathy, often in the acute setting. Optic nerve atrophy is chronic volume loss that can occur from prior insult. It can be hard to determine which of the nerves is abnormal when they are asymmetric.

Optic nerve sheath and retroorbital fat

The optic nerve sheath and periorbital fat are subject to different pathologies, including perineuritis, idiopathic orbital inflammation, sarcoid, certain tumors such as meningioma, lymphoma, and metastatic disease, and idiopathic intracranial hypertension.

Globes

The globes can be affected by inflammation, tumors, and degenerative changes. Inflammation can affect the entire globe or only portions, such as the posterior sclera. Phthisis bulbi is a chronic atrophy of a non-functional globe. Melanoma is a relatively common malignancy of the uvea, but can be hard to see. It is sometimes manifested as an intrinsic T1 hyperintense mass. Retinal detachment can often be seen on MRI as well.

Orbital apex

Cranial nerves and vessels are the main things passing through the orbital apex, and pathologies that you see probably arise from one of them. Slow flow venous malformations (previously called hemangiomas) are well circumscribed vascular lesions often occurring in the orbital apex and orbit. Masses such as meningioma also occur at the orbital apex.

Extraconal compartment

The extraconal structures include the muscles, lacrimal ducts, fat, and the periosteum. A common cause of extraocular muscle abnormality is thyroid ophthalmopathy, which causes bilateral symmetric enlargement that spares the myotendinous junction. Lymphoma can cause masses of the extraocular muscles or lacrimal ducts and often restricts diffusion. Infection can extend from the sinuses into the extraconal compartment and even extend intracranially. The lacrimal glands are subject to their own specific pathology. They can get inflammatory changes related to idiopathic orbital inflammation or sarcoidosis. Dermoids are well-defined masses in the orbit, likely near suture lines. Osseous lesions can also extend from the orbits into the orbital walls.

Conclusion

Hopefully you learned a little bit about the anatomy and common pathology of the orbit. Be sure to check out the other videos on search patterns as well as all the other head and neck topics.

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