Can we make an accurate diagnosis of pyriform sinus fistula by fetal MRI?

Aim: To review the fetal magnetic resonance imaging (MRI) features of pyriform sinus fistula (PSF) and to compare them with the postnatal clinical and surgical findings. The relevant medical literature is also discussed. Materials and methods: The location, shape, signal, effects of adjacent structures and in utero changes detected on fetal MRI were reviewed in three cases of PSF. The patient's respiratory status at birth, the application of ex utero intrapartum therapy (EXIT), infectious complications in the neonatal period, and the surgical and pathological findings were also reviewed and discussed. The study consisted of three pregnant women between 18 and 38 years of age, each with a single fetus. Fetal MRI was performed at 26 and 38 weeks of gestation in case 1, at 34 weeks of gestation in case 2, and at 34 and 38 weeks of gestation in case 3. Postnatal clinical follow-up extended from 9 months to 3 years. Results: All lesions were well-circumscribed unilobular cysts with slightly thickened walls at the neck area. Case 1 was irregular in shape, and the other two cases were oval and extended longitudinally along the neck. The fluid contents showed signals consistent with amniotic fluid. Close contact with the thyroid gland was demonstrated to be a fairly characteristic feature that could be recognised on fetal MRI. The in utero follow-up detected slight changes in the signal, wall characteristics, contour, and airway deviation. Case 1 was bilaterally affected, causing it to be initially mistaken as macro-cystic lymphangioma. The diagnosis was corrected with the aid of postnatal imaging; however, a prenatal diagnosis was correctly made in cases 2 and 3. Airway obstruction was not observed in any of the three cases, and thus, EXIT was not applied. The fetal MRI findings were in good agreement with the postnatal clinical and surgical findings. In addition to the higher spatial delineation provided by fetal MRI, as described in the literature, the observation of close contact with the thyroid gland and a flattened deformity of the thyroid gland are other characteristic features. Conclusion: Fetal MRI is useful for displaying characteristics of PSF that can enable an accurate prenatal diagnosis. - Highlights: • Features of pyriform sinus fistula on fetal imaging are comprehensively evaluated. • Another two prenatal cases were diagnosed accurately after a last reported one. • Fetal MRI is good at differentiating cystic masses at the neck area prenatally. • Fetal MRI is good at displaying the airway status to assess the need of EXIT. • A correct diagnosis is fundamental to valid medical procedures after birth.