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Notizen: Abstract: Invasive lobular carcinoma (ILC) may be a difficult tumor to detect early by physical examination, mammography, or ultrasound. We undertook this study to describe the spectrum of gadolinium enhancement and morphologic features of ILC on magnetic resonance imaging (MRI). Nineteen patients with ILC who presented with a palpable mass, a mammographically visible abnormality, or an unknown primary underwent preoperative MRI of both breasts using a T1-weighted high-resolution gradient echo sequence (pre- and postcontrast), and an echoplanar sequence during the administration of gadolinium. Using a quantitative measure of gadolinium uptake over time, called the extraction flow (EF) product, and a normal tissue threshold EF level of 25 or less, enhancement for 15 of the 19 cancers was characterized. By consensus, three radiologists categorized the morphologic features of the lesions. For the 15 cases of ILC that had echoplanar data, analysis showed peak EFs ranging between 25 and 120, and the majority showed EFs in the 30s. A substantial portion of two tumors enhanced in a similar fashion to normal breast tissue, with EFs in the low 20s. Morphologically MRI showed a focal mass in eight cases, regional enhancement in five, segmental enhancement in one, segmental enhancement with multiple small nodules in one, a mixture of a focal mass and regional enhancement in one, diffuse enhancement in one, multiple small nodules in one, and bilateral disease in one. Of the focal masses, seven were irregular in shape and one was round; six had ill-defined margins and two had spiculated margins. All eight enhanced heterogeneously. Four cases had multifocal disease and one case had unsuspected contralateral disease discovered only on MRI. MRI using a combination of morphology and a quantitative measure of gadolinium uptake was able to detect the majority of cases of ILC. However, there was a variable morphologic appearance and contrast enhancement pattern on MRI. A few lesions were difficult to distinguish from normal tissue. This suggests that some cases of ILC may be difficult to detect on MRI.