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 4th 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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