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Incomplete partition type II in its various manifestations: isolated, in association with EVA, syndromic, and beyond; a multicentre international study

  • Paediatric Neuroradiology
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Incomplete partition type II (IP-II) is characterized by specific histological features and radiological appearance. It may occur in isolation or in association with an enlarged vestibular aqueduct (EVA). Among those with IP-II and EVA, a subset has a diagnosis of Pendred syndrome. This study aimed to explore the prevalence of isolated IP-II, IP-II with EVA, and cases with a genetic or syndromic basis in our cohort.


From a large, multicentre database of dysplastic cochleae (446 patients, 892 temporal bones), those with imaging features of IP-II were examined in detail, including whether there was a genetic or syndromic association.


A total of 78 patients with IP-II were identified. Among these, 55 patients had bilateral IP-II and EVA (only 12 with typical Mondini triad), 8 with bilateral IP-II and normal VA, 2 with bilateral IP-II and unilateral EVA, and 13 with unilateral IP-II (9 with unilateral EVA). Among the group with bilateral IP-II and bilateral EVA in whom genetic analysis was available, 14 out of 29 (48%) had SLC26A4 mutations and a diagnosis of Pendred syndrome, 1 had a FOXI1 mutation, and a few other genetic abnormalities; none had KCNJ10 pathogenic variants.


Bilateral IP-II-bilateral EVA may be seen in the context of Pendred syndrome (SLC26A4 or FOXI1 mutations) but, in the majority of our cohort, no genetic abnormalities were found, suggesting the possibility of unknown genetic associations. IP-II in isolation (without EVA) is favored to be genetic when bilateral, although the cause is often unknown.

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Research reported in this publication was supported by the National Institute of Health Biomedical Research Center at Great Ormond Street Hospital, London UK (unfunded).

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Correspondence to Amy F. Juliano.

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All procedures performed in the studies involving human participants were in accordance with the ethical standards of the institutional research committee (Clinical Research Adoption Committee) and with the 1964 Helsinki Declaration and its later amendments.

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Standard clinical informed consent was obtained at the time of the scan. Informed consent for this specific study was not applicable given the retrospective nature of this research.

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Supplementary Fig. 1

: Bilateral IP-II bilateral EVA phenotype in a patient with Pendred syndrome. Axial temporal bone CT scans showing bilateral EVA (thin arrows) and the rounded appearance of the apex of the cochleae, indicative of IP-II (thick arrows)”.

Supplementary Fig. 2: unilateral IP-II, enlarged vestibule and enlarged endolymphatic sac (i.e. unilateral “Mondini malformation”). Axial source images from a 3D CISS sequence in a 3-month-old female with left hearing loss showing unilateral IP-II (long arrow) and mild enlargement of the vestibule (when compared with the contralateral vestibule). Note is made of the extremely hypoplastic modiolus and mildly enlarged endolymphatic sac (short arrow).

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D’Arco, F., Kandemirli, S.G., Dahmoush, H.M. et al. Incomplete partition type II in its various manifestations: isolated, in association with EVA, syndromic, and beyond; a multicentre international study. Neuroradiology 66, 1397–1403 (2024).

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