What differentials would you entertain?
The differential is long but is limited to non-aggressive lesions. Epidermoid/dermoid is most likely given the increased T1 signal, margins and location. Mucocele, however it is very lateral and no definite communication with the right frontal sinus is identified. . Eosinophilic granuloma would usually demonstrate more enhancement and usually is not associated with bone expansion. Fibrous dysplasia in this age group is usually not cystic. Haemangioma would demonstrate more enhancement. Leptomeningeal cyst is unlikely without a history of trauma/intracranial cystic component.
MRI demonstrates an expansile lesion centred in the right frontal bone adjacent to the right frontal sinus measuring 4.4cm * 1.9cm). It is well-defined. There is some extra-osseous extension into the subcutaneous tissue (best seen on the T2 GRE images). It is hyperintense on T2 weighted imaging, iso-intense on T1 weighted imaging. It is of intermediate signal on DWI without associated decreased in ADC values.
Within it there is dependant / posterior debris seen within it which is hyperintense on T1 imaging. The periphery of this lesion enhances. There dura / periosteum seen adjacent to this lesion (intracranial and intra-orbital) demonstrates enhancement. No flow voids seen within this lesion. The pituitary stalk is normal. No other lytic lesions seen within the visualised skull.
The visualised brain has normal appearances.