Ecchordosis physaliphora and its variants: proposed new classification based on high-resolution fast MR imaging employing steady-state acquisition

To propose a new classification for ecchordosis physaliphora (EP) using fast imaging employing steady-state acquisition (FIESTA). We evaluated 974 consecutive patients and selected for further study 78 (8.0 %) who manifested an excrescence on the dorsal surface of the clivus (DSC) and/or clivus lesions. Lesions were defined as "classical EP" when they appeared as a hyperintense excrescence (cyst-like component) on DSC. Other lesions were defined as "possible EP". Of the 78 patients, 17 (22 %) were diagnosed with classical EP, the other 61 with possible EP. The 61 patients with possible EP were further classified into "incomplete EP = EP bud" (n = 55, 90.2 %), characterised by a T2 hypointense protrusion of the clivus, and into "EP variant" (n = 6, 9.8 %), characterised by hyperintense lesions within only clivus. FIESTA findings of incomplete EP were similar to those of classical EP except for lack of the hyperintense excrescence on DSC. Most lesions were located at the level of the Dorello canal at the midline of the craniospinal axis. Our results suggest that the magnetic resonance imaging appearance of EP is diverse. Based on our FIESTA results we propose a new classification for EP, i.e. classical EP, incomplete EP (EP bud) and EP variant. Ecchordosis physaliphora (EP) is a rare benign cystic congenital lesion arising from notochord. The classical type of EP is frequently associated with a T2 hypointense protrusion. T2 hypointense protrusions without clivus cysts may represent an incomplete type of EP. Third type of EP variant only harbours lesions within the clivus.