- •While considered essentially pathognomonic of Rathke’s cleft cysts, the presence of an intracystic nodule on MRI – the so-called ‘dot’ sign – has not been comprehensively described for colloid cysts of the third ventricle.
- •Here, we retrospectively characterized the prevalence and MRI characteristics of the ‘dot sign’ in colloid cysts at a single-institution.
- •The ‘dot sign’ was observed in 38% of radiologically verified colloid cysts – the ‘dot’ displayed low intensity with respect to cyst fluid on T2-weighted sequences in all cases.
- •An intracystic low T2 ‘dot’ is a common MRI feature of colloid cysts of the third ventricle, and to our knowledge not previously systematically described.
To determine the incidence of the ‘dot sign’ in patients with colloid cysts of the third ventricle and to characterise its MRI appearances.
Materials and Methods
Single institution retrospective analysis between January 2007 and October 2016 of all patients with either an imaging or imaging and histology-confirmed diagnosis of colloid cysts of the 3rd ventricle was undertaken. For all cases, MRI signal intensities of the cyst fluid component were graded by two independent radiologists relative to brain parenchyma. Presence of a dot, and if present, its size and relative position within the cyst were recorded. Signal intensities of the dot were then similarly assessed.
37 cases of colloid cyst were identified. Of these 37.8% (n = 14) demonstrated the dot sign. The majority (11 of 14) were observed inferiorly within the cyst; two cases were anteroinferior, and one other was posterior. All identified intracystic nodules displayed low signal intensity with respect to cyst fluid on T2 weighted sequences, and only two nodules were hypointense to fluid on T1-weighted imaging, with the remainder either iso- or hyperintense.
An intracystic low T2 ‘dot’ is a common MRI feature of colloid cysts of the third ventricle, and to our knowledge not previously systematically described. Presence of such a dot should not only not dissuade from a diagnosis of colloid cyst being made, but should in fact be used to strengthen the imaging diagnosis.
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Published online: November 26, 2018
Accepted: November 10, 2018
Received: September 25, 2018
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