Studies

Conventional ultrasonography versus Tissue Harmonic Imaging for the assessment of the common bile duct in cholecystectomized patients



Discussion

The results obtained demonstrate the superiority of harmonic imaging over conventional US in the study of the common bile duct in patients who have undergone cholecystectomy.

In particular, the better axial and lateral resolution, the reduction in background noise and the better signal-tonoise ratio facilitate the study of the common bile duct even in the distal third, although as regards the interposition of air-filled structures harmonic imaging suffers the same limitations as conventional imaging.

It should also be recalled that the presence of scars and internal adhesions in patients who have undergone cholecystectomy, whether laparotomic or laparoscopic, hampers the examination by conventional ultrasonography, as do obesity and the poor co-operation of elderly patients. The use of THI lessens the impact of these unfavourable conditions.

Observation of the intraand extrahepatic bile ducts is easier with THI as these structures are at a depth where the intensity of the harmonic echoes is greatest. Because the production of these echoes is weaker in the deeper layers, harmonic imaging is less useful in the study of deep structures. In particular, in the study of the common bile duct, the reduction in background noise and the better signal-to-noise ratio typical of harmonic imaging allow greater diagnostic confidence in excluding or identifying the presence of stones.

For the preoperative, perioperative and intraoperative study of the choledocus, alternative methods to conventional ultrasound have been proposed in the past few years. In the preoperative phase, ERCP has recently been successfully associated with Magnetic Resonance imaging in the perioperative planning of video-laparoscopic cholecystectomy.

The introduction of this approach to cholecystectomy has promoted the development of other perioperative diagnostic imaging methods, such as endoscopic ultrasound and laparoscopic ultrasound whose use is, however, confined to a few specialised centres [23-30].

In the postoperative phase, MR-cholangiography and ERCP, which are recognised as the gold standard in the study of the bile ducts, are respectively limited by high cost and suboptimal visualisation of the bile ducts in the presence of metallic clips, and by an unacceptable degree of invasiveness for the routine imaging of patients who have undergone cholecystectomy.

The study of the patient who has undergone cholecystectomy therefore requires a widely available method, which is easily reproducible and capable of providing results with a high level of diagnostic accuracy. THI allows a more adequate study of the choledocus and in particular reduces dependence of diagnostic results on the operator’s experience.

Acknowledgements.—The authors thank Dr. Matteo Bottai, CNR (Consiglio Nazionale delle Ricerche) Pisa,Via Maruzzi 1, 56100 Ghezzano, PISA for providing the statistical analysis.