Ecchordosis physaliphora: typical and atypical radiologic features.

Ecchordosis physaliphora (EP) is a distinct clinical entity defined as a notochordal remnant found on the dorsal surface of the clivus, occurring in about 2 % of autopsies. The aim of this study is to introduce typical and atypical imaging features of EP, which can be confused with those of clival chordoma. Forty-one patients with clinical suspicion for clival chordoma visited the outpatient clinic from June 2007 to August 2015. A retrospective review was performed with magnetic resonance imaging (MRI) and computed tomography (CT) studies to revise the diagnosis to EP. Eight of 41 patients (19.5 %) manifested lesions on the dorsal surface of the clivus that were well circumscribed and homogenous, with no septations or osteolysis. The lesions were all hypointense on T1, hyperintense on T2-weighted MRI, and had no enhancement with gadolinium. A distinct T2-hypointense pedicle, which is the hallmark of EP, was seen in five patients (62.5 %) and defined as typical EP. A characteristic T2-hypointense rim was observed in three patients and defined as atypical EP (37.5 %). The mean largest diameter of the lesions was 1.1 cm (0.6-1.8 cm). Lesion size did not change in all the patients who were followed for a mean of 3.6 years (1.4-8.2 years) by separate MRI scans performed every 6 months to 1 year. EP and clival chordoma represent different spectra of the same pathology. As the two lesions have completely different prognoses, precise knowledge of the imaging features of EP is very important. Accurate diagnosis is essential for proper treatment planning.