Transperineal ultrasound in perianal fistulas & abscess

Dr.Priyatamjee Bussary

I. Introduction

Transperineal ultrasound(TPUS) is an sonographic technique used in the detection of conditions around anal canal and pelvic floor.It is a simple,fast and well tolerated technique which detects , evaluates and classifies perianal fistulas and abscesses, which are two common yet serious conditions that can cause severe pain and discomfort.This scan is as reliable as MRI in diagnosing perianal conditions.

A. What is the transperineal ultrasound?

Transperineal ultrasound is a non-invasive imaging technique used to diagnose and monitor conditions associated with perianal region. It can be used to detect and evaluate infections such as abscesses and fistulae. The procedure involves scanning perineum with an ultrasound probe to produce images surrounding anal canal. This technique has become increasingly popular due to its ability to accurately identify anatomical features and provide detailed information and pathology without requiring MRI.

Transperineal ultrasound vs Endoanal ultrasound EUS

Endoanal ultrasound offers 360° view of anal canal and the whole perineum. It is considered a gold standard for evaluation of fistula however it has few limitations.

Limitations of EUS

Penetration of endoanal transducers are limited and hence may not trace the entire extrasphincteric fistulous tract
Severe painful conditions like anal fissure & abscess are not well tolerated by patients who want to undergo endoanal usg
Availability of equipment-very few ultrasound equipment vendors have 360° endoanal transducers
Endoanal transducers are difficult to manufacture and hence are 3-5 times expensive compare to regular transducers.

B. Overview of perianal abscess & fistulas

Perianal fistulas and abscesses are infective & inflammatory conditions that occur in perineum. Perianal abscess is collection of pus caused by bacterial infection, while perianal fistula is an abnormal connection between skin and anal canal.

Perinal fistulas can be classified into intersphincteric,transsphincteric, suprasphincteric and extrasphincteric fistulas.

Perianal abscess can be crypt abscess, intersphincteric,ischioanal,ischiorectal and superficial abscess.

Imaging techniques such as magnetic resonance imaging MRI, endoanal ultrasound, perineal ultrasound TPUS can be used to diagnose these conditions. Treatment typically involves drainage of the abscess or surgical removal of the fistula tract. In some cases antibiotics,analgesics may be prescribed to help reduce infection & inflammation. Perianal abscesses and fistulas can cause long-term problems if left untreated so it is important for individuals to seek medical attention if they experience any signs or symptoms associated with these conditions.

II. Benefits of Transperineal Ultrasound in Diagnosis of Perianal Abscess & Fistulas

A. Accuracy of diagnosis

"TPUS showed sensitivity of 50.00%, specificity of 92.31% and accuracy of 86.67% in detection of side branches."Hence it is fairly accurate, reliable and specific when done correctly. In most cases, diagnosis can be sensitive enough to detect even the early crypt abscess at the begenning of the symptoms.

transperineal ultrasonography can accurately differentiate between different types of fistulas. It also allows them to make decisions about treatments quickly and effectively. With the right tools and training, diagnosing a patient can be done with utmost accuracy and reliability.

B. Easier visualization of deeper structures

Transperineal ultrasound can easily detect perianal infections in superficial structures like anal canal and vagina. Visualization of deeper structures, such as rectum and prostate can be challenging.

III. Procedure Description

A. Preparation for the exam

There is no need for any special preparation. No Fasting needed. It is also important to take any medications prescribed by the doctor in order to manage any pain or other symptoms.

B. What to expect during the exam

Doctor may also ask few questions about any symptoms experienced by the patient in order to get a better idea of what could be causing them.During the exam, patient will be asked to lie down in lithotomy position and doctor will expose and clean the area if needed. Digital rectal examination is performed to assess any tenderness or mucosal changes in anal canal. A probe with small amount of jelly is used to glide over the perineum.Patient may experience some discomfort during the procedure, but it should not be painful. The entire process may take around 20-30 minutes.

IV. Limitations

Resolution of TPUS is limited when compared to EUS

Ultrasound cannot differentiate between a small abscess and fibrous tissue, as both are hypoechoic.

Fistula with internal opening at rectal wall cannot be optimally visualised due to air shadows.

Severe perineal pain can limit optimal evaluation of perianal abscess.

V. Conclusion

Transperineal ultrasound (TPUS) is a fast and simple sonographic technique used to detect and classify perianal fistulas and abscesses, which can cause severe pain and discomfort. It is as reliable as MRI in diagnosing perianal conditions. TPUS is a valuable and accessible diagnostic tool that can lead to more effective treatments and better outcomes for patients.

References

1.Roman Boles, M.S., Awadallah, M.Y., Shawali, H.A.S. et al. Role of transperineal ultrasound in evaluation of patients with perianal inflammatory disorders. Egypt J Radiol Nucl Med 53, 141 (2022). https://doi.org/10.1186/s43055-022-00812-1