In which situation is additional imaging typically required after a mammogram?

Additional imaging is typically required when a lesion is only seen in one projection during a mammogram. This situation suggests that there might be an area of concern that requires further investigation to ascertain the nature of the lesion. Lesions that appear on a single view might be benign but could also indicate potential malignancy that needs confirmation. Therefore, supplementary views or different imaging modalities such as breast ultrasound or MRI may be performed to obtain a more comprehensive assessment of the breast tissue and to determine whether the lesion warrants further action or monitoring.

In contrast, while dense breast tissue can complicate interpretation and may warrant additional imaging, it is not a definitive reason for additional imaging since not all dense tissue correlates with lesions. Being under 40 years old does not automatically necessitate further imaging as the decision is primarily based on findings rather than age alone. The unavailability of an imaging technician is also not a clinical reason to pursue additional imaging; rather, it would simply delay the process until a technician is available. Hence, the requirement for additional imaging primarily arises when a lesion is only detected in one projection, directing the need for a clearer understanding of the area in question.