Magnetic Resonance Imaging for Stage IV Melanoma During Pregnancy

In their recent article, Beyeler et al¹ conclude that “staging procedures must avoid ionizing radiation” and state that “magnetic resonance imaging [MRI] is harmless to the fetus.” This statement is misleading.

In the United Kingdom, the National Radiological Protection Board (NRPB), now the Radiation Protection Division of the Health Protection Agency, suggests that pregnant women should not be offered MRI in the first 3 months of pregnancy. Although the results of studies on mammals were mostly negative, the National Radiological Protection Board considered it prudent to avoid MRI of pregnant women during the first trimester, until the consequences of exposure to time-varying magnetic field gradients become more clearly established. The radiofrequency fields used during MRI can cause heating effects in the mother and fetus. These, in turn, can cause adverse effects that may be avoidable if the temperatures in the tissues do not exceed 38°C. On this basis, the NRPB concluded that until further information becomes available, pregnant women should not undergo MRI in the first 3 months of pregnancy unless the only reasonable alternative imaging method involves the use of x-ray procedures.

This advice still stands, and since the 1991 NRPB report,² there have been strong concerns about the risk to the fetus when the mother is exposed to high noise levels such as can occur during MRI. Exposure to excessive noise during pregnancy may result in high-frequency hearing loss in newborns and may be associated with prematurity and intrauterine growth retardation.^{3 - 4}

Magnetic resonance imaging in pregnancy is safer than techniques such as computed tomography, which involve ionizing radiation, and it is still the method of choice in the assessment of possible nodal disease in the abdomen and pelvis. Ultrasound may miss significant lymphadenopathy, which can potentially be obscured by the gravid uterus. Magnetic resonance imaging should not, however, be considered harmless to the fetus. This suggestion may encourage its use in pregnant patients with more minor diseases than stage IV melanoma. Computed tomography of the chest may still be required, because intrapulmonary metastases are not always visible on MRI; however, by careful attention to technique, the radiation dose to the fetus can be minimized without compromising diagnostic accuracy.

Dr Beyeler and colleagues suggest that to evaluate risks properly and to counsel the patient and her family appropriately, a collaborative approach by dermatologists, oncologic surgeons, obstetricians, and neonatologists is required. We suggest that radiologists should be included in this group to ensure an appropriate imaging strategy. Such an approach would minimize the risk to the fetus yet still allow adequate assessment of the mother, thereby optimizing the health and survival of both.

Correspondence: Dr C. Campbell, Department of Radiology, Southern General Hospital, Govan Road, Glasgow G51, Scotland.

Financial Disclosure: None.