This 56 year-old male patient presented with headaches and a long history of progressive spastic paraparesis. An incidental finding on MR of brain and spine was a lesion in the region of the cribriform plate which was of high signal on T2 and FLAIR, and intermediate signal on T1. The appearance is typical of a small mucocoele. The differential diagnosis includes encephalocoele. There appears to be a bony plate between the lesion and adjacent frontal lobe, making encephalocoele less likely.

Mucocoeles are due to blockage of a sinus ostium and filling of the sinus with mucus, which acts as a slow-growing mass lesion. Posterior ethmoidal mucocoeles may cause pressure effects on the optic nerve. Frontal or anterior ethmoidal mucocoeles may expand into the orbit to cause proptosis. Infection of a mucocoele is a surgical emergency as rapid spread of sepsis may occur.

CT is most useful for diagnosis, as the characteristic sinus expansion and bone thinning is demonstrated. Mucocoeles are often of high signal on T1 due to the high protein content.

Reference: Grainger RG, et al. Diagnostic Radiology: A Textbook of Medical Imaging. 4th edition. Churchill-Livingstone 2001

Credit: Dr Laughlin Dawes