Jessica Williams, MD, Addresses Most Common Radiology Questions From Dermatologists

When pediatric dermatologists need a deeper look into their patient’s conditions, radiology can be enlightening. Jessica Williams, MD, of Radiology Associates of Albuquerque, New Mexico, joined the 2023 Society for Pediatric Dermatology Meeting on July 15 to offer insights into when to use radiology, how to order it, when to order contrast, and the best imaging for particular situations.¹

Ultrasound

Williams began her presentation discussing ultrasound. She said it is wonderful for kids and adults for a number of reasons. It does not require sedation, there is no radiation, and it is cost-effective. “If you remember nothing else that I say about ultrasound during this lecture, remember that ultrasound is like shining a flashlight in a dark room. You’re only going to see where it’s pointing the beam, so it helps to know where to look,” said Williams.

She emphasized that ultrasound is great for lumps and bumps, and for follow-up of a known abnormality that has already been identified by MRI or CT. For imaging of the spinal cord, ultrasound is preferably done before 3 months of age and definitely no later than 6 months because once the posterior elements of the spine ossify, the spinal cord can no longer be seen.

To distinguish between solid and cystic lesions, color Doppler can be added. By adding spectrum or Pulse Wave Doppler, providers can differentiate between arterial venous flow. Based on results, more advanced imaging can be ordered when necessary.

Williams’ take-away pearl on ultrasound was, “There is a subsequent discrepancy in diagnostic capabilities of cutaneous ultrasound in radiology departments.”

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Magnetic Resonance Imaging (MRI)

She continued her session by describing MRI as a great tool for distinguishing between different types of soft tissue contrast resolution. It offers a wider field of view than ultrasound and has no ionizing radiation. However, MRI is more costly and requires sedation or immobilization because of the longer time to obtain the MRI. In the first 3 months of life, imaging can be done without sedation using a swaddling technique. MRI provides excellent detail for surgical planning and can be used with ultrasound.

The pearl regarding this imaging is, “MRI is the best modality when the anatomy is complex.”

MRI Contrast Media

Adding contrast media to MRI provides a wealth of information. Lesions that would not be seen without Intravenous contrast agents can be detected. For lumbosacral anatomy (LUMBAR), head and neck anatomy, (PHACE), orbital lesions, and joints, MRI is preferred.

Williams discussed the controversy of gadolinium-based contrast media (GBCM) because of toxicity. However, she noted that the American College of Radiology (ACR) and the National Kidney Foundation (NKF) released a consensus statement. She summarized that, “Since the risk of NSF is so low with group II GBCM, the potential harms of delaying or withholding group II GBCM for an MRI in a patient with acute kidney injury or eGFR less than 30 mL/min per 1.73m2 is likely to outweigh the risk in most clinical situations.”

Williams offered two pearls regarding ordering contrast with MRIs. First, “Contrasted MRIs are always ordered without and with contrast.” She added that non-contrasted sequences are necessary to compare with post-contrast, however, this is not true with CT, where a multiphasic scan at a minimum doubles the radiation dose. Her second pearl was that an additional order may be required to add an MRA.

There are situations when contrast should not be ordered. These include when follow-up of a diagnosed vascular anomaly is being done for response to treatment, in surveillance of diagnosed optic pathway gliomas, and surveillance for subependymal giant cell astrocytoma (SEGA).

Special Cases 

Regarding neurocutaneous melanosis, Williams said a non-contrast brain MRI should be done in all patients with giant melanocytic nevi. This is best performed in the first 1 to 3 months of life. At that age, sedation is often not required and melanosis is most easily identified. If imaging is performed later in the first year, contrast is recommended.

Williams next discussed tuberous sclerosis, recommending that a follow-up brain MRI without contrast is performed every 1 to 3 years until the patient reaches age 25. Children with SEGA who begin treatment pre-symptomatically have better outcomes than those treated once symptoms appear.

She next talked about Stuge-Weber syndrome. She explained that “screening for brain involvement is not recommended in newborns and infants with a high risk of PWB and no history of seizures or neurological symptoms.” If treatment is being considered before the appearance of symptoms, however, routine screening should be considered.

Computed Tomography (CT)

Williams concluded her session discussing the pros and cons of CT scans. She said they are better than an MRI for spatial resolution and CT is fast. On the negative side, there is ionizing radiation. She said they are best for cortical bone, such as ACC skull defect.

Reference

1. Williams J. Radiology for pediatric dermatologists: Should I order contrast? Your radiology questions answered. Presented at the 2023 Society for Pediatric Dermatology Meeting; July 13-16, 2023. Asheville, NC.