The bell-clapper deformity of the testis: The definitive pathological anatomy.

Introduction: The bell-clapper deformity (BCD) predisposes to intravaginal torsion (IVT) and is classically bilateral. The precise pathological definition of what constitutes a BCD is not clear. The current study aims to clarify the specific anatomic details of this anomaly.
Methods: A systematic review was performed utilizing the PRISMA principles. Studies are presented chronologically based on their level of evidence. They are further divided into study types: autopsy and operative studies of acute torsion, intermittent torsion and studies of the contralateral testis in vanishing testis.
Results: The bell-clapper deformity is best defined by complete investment of the testis, epididymis and a length of the spermatic cord by the tunica vaginalis. Based on autopsy studies the rate of BCD in scrotal testis varied from 4.9% to 16%; with bilaterality in 66%-100%. In cases of acute IVT bilaterality was noted in 54%-100%. The most disparate results were in cases of testicular regression syndrome where contralateral BCD was noted in 0%-87% of cases.
Conclusion: We suggest future studies employ the strict anatomical definition above. As there is evidence of age-dependent investment of the testes, it will be important to develop age-standardized measurements of intravaginal length of spermatic cord. This critical morphometric measurement will allow a better understanding of the risk of IVT.
Level of Evidence: Systematic review of diagnostic studies: lowest level of evidence of included manuscripts Level IV (case-control studies with a poor reference standard).
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