FLEX February 2024

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Fig. 4. Second branchial cleft cyst. Axial ( A ) and recontructed sagittal ( B ) contrast-enhanced CT images show a unilocular low density collection at the angle of the mandible, postero lateral to the submandibular gland ( curved white arrow ), and anteriomedial to the SCM ( curved black arrow ).

tracts may be collapsed, rendering them difficult to identify on any imaging modality. Uncomplicated branchial cleft cysts appear as hypoattenuating lesions with a thin wall ( Fig. 4 ). In cases of infected branchial cleft cysts, CT demonstrates a hypoattenuating cystic lesion, which may have a thickened wall, and inflammatory changes in the sur rounding soft tissues ( Fig. 5 ). MRI may be helpful in evaluating atypical features of branchial cleft cysts, which can result from intracapsular hemorrhage or solidification of cystic fluid, appearing as abnormal signal intensities of the contents ( Fig. 6 ). In particular, intracystic hemor rhage can demonstrate hyperintensity on T1 and T2 weighted images, while solidifica tion of cystic fluid displays homogeneous hypointensity on T2 weighted images without enhancement. 16 Atypical branchial cleft cysts can be difficult to differentiate from cystic malignancies even on MRI, and tissue sampling may ultimately be necessary. 17

Fig. 5. First branchial cleft cyst. Axial ( A ) and recontructed coronal ( B ) contrast enhanced CT images demonstrate a low-density periauricular cyst ( white arrows ) adjacent to the external auditory canal (EAC) with inflammatory changes of the surrounding soft tissues.

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