Two Birds, One Hydrodissection - Riché-Cannieu Anastomosis identified with Carpal Tunnel Hydrodissection: A Case Report

Case Diagnosis: Riché-Cannieu Anastomosis with concurrent Carpal Tunnel Syndrome

Case Description or Program Description: 34 yo right-hand dominant, male presented for evaluation of carpal tunnel syndrome d/t endorsing pain and numbness in the median nerve distribution. EMG consistent with severe CTS. Diagnostic Ultrasound demonstrated CTS, but inconsistent to the severity demonstrated on EMG. Patient elected to undergo hydrodissection for symptomatic relief, 5cc total injectate of 4cc 1% lidocaine and 1cc 40mg/mL Triamcinolone, resulted in complete numbness of the hand, instead of strictly the median nerve distribution that would be expected under normal anatomic conditions.

Setting: Outpatient

Assessment/Results: Riché-Cannieu Anastomosis was identified from patient endorsed symptoms s/p hydrodissection and the evidence noted on EMG severity that was inconsistent with visualized CTS severity on diagnostic ultrasound.

Discussion (relevance): Riché-Cannieu Anastomosis (RCA) is a normal anatomic variant that can create confusing clinical, electromyographic, and surgical findings. In the past it has been argued as a rare variant, while more recent literature has documented its presence in 100% of cadavers to varying degrees, such as in the study by Caetano et al. RCA can be misdiagnosed as severe CTS when EMG is performed over the wrist/median nerve, which can result in unnecessary surgical intervention. On diagnostic ultrasound, our patient did have evidence of focal compression and adhesions of the median nerve, with proximal edema from the lesion which is why minimally invasive hydrodissection d/t failure of conservative treatment measures was performed that then revealed the RCA. It is for these reasons, between literature documenting higher rates of prevalence than formerly believed and in settings when EMG is not consistent with diagnostic imaging, that RCA should be further considered.

Conclusions: Riché-Cannieu Anastomosis is an important anatomical variant that should be considered when working up patients for median and ulnar neuropathies, as its presence can pose challenges in accurate diagnosis and in turn, appropriate intervention.