FLEX February 2024

Stern et al

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Fig. 23. Langerhans cell histiocytosis. Axial fat-suppressed postcontrast T1 weighted MRI shows an expansile enhancing lesion in the left frontal calvarium, with an associated soft tissue mass extending into the left frontal extracranial soft tissues ( arrow ).

On MRI, the skull lesions often have intermediate signal on T1 weighted images, intermediate-to-high signal on T2 weighted images; they demonstrate enhancement on postcontrast T1 weighted images. Furthermore, Langerhans cell histiocystosis can display diffusion restriction, a feature that can be seen with malignant lesions ( Fig. 23 ). 20 The boundaries of the skull and extracranial head and neck lesions are well delineated on MRI, specifically with fat-suppressed postcontrast T1 weighted sequences, which are helpful in elucidating commonly associated soft tissue masses. Similarly, MRI is an excellent modality for evaluating intracranial involvement. 29,30

Fig. 24. Juvenile nasopharyngeal angiofibroma. Axial noncontrast CT image in bone algo rithm demonstrates widening of the right pterygopalatine fossa with associated bony erosive changes.

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