Perianal inflammatory disorders include perianal fistulas, ano-vaginal, rectovaginal fistulas, perianal abscesses, and perianal sinus tracts. These inflammatory conditions are in fact very challenging for surgeons as they have high tendency to resist treatment, recur after surgery and transform into a chronic inflammatory condition, which results in subsequent multiple surgeries, associated morbidities to the patient and high cost of recurrent hospitalizations [7].
Although MRI of the anal canal is the modality of choice in cases of perianal inflammatory disorders, it remains difficult to be applied in the necessary regular follow-up of these cases because of its high cost and limited availability in many centres [8]. Besides, despite EAUS is recommended in these cases, it is unsafe to be used in patients with anal strictures or anal pain which are considered frequent symptoms in these patients. Furthermore, EAUS is unable to assess pathologies away from the anal canal such as gluteal or scrotal lesions [3].
Consequently, a simple available and cheap diagnostic tool is mandatory for precise diagnosis and regular follow-up along the course of management of the perianal inflammatory disorders to ensure good healing, reduce the rate of recurrence, comorbidities and costs of repeated hospitalizations. Accordingly, the aim of our study was to assess the accuracy of TPUS in evaluation of perianal inflammatory disorders, helping the surgeon in decision of the appropriate surgical procedure and regular follow-up along the course of their management.
Regarding our approach, the radiologist who performed TPUS examination was blinded to MRI findings, in contrast to Fateh MS who declared that both TPUS and MRI examinations were interpreted by the same radiologist [9].
In our study, we have not instilled any injectable materials except for a case of high tract in which we injected only saline via the skin opening to distend the tract and visualise site of the internal opening (Fig. 2). Some researchers recommended the instillation of hydrogen peroxide through the skin opening of perianal fistula for better visualisation of its internal opening and side branches [3]; however, we preferred to avoid injection of hydrogen peroxide because it was reported by some authors that injection of hydrogen peroxide may cause series of artefacts degrading the image quality [10]. Besides, Nevler A. et al. concluded in their study that instillation of hydrogen peroxide have not improved visualisation of the side branches of perianal tracts [11].
Regarding our results in detection of the exact site of the internal opening of perianal tracts, which is considered one of the important risk factors of recurrence [2]; TPUS correctly detected the exact site of internal opening in (21/30, 70%) patients, which is comparable with Nevler A. et al., who reported that TPUS correctly predicted the presence and location of the internal opening of perianal tracts in 16/22 (72.3%) patients [11].
Our study showed that TPUS showed accuracy of 83.33%, with high sensitivity of 91.30% in detection of the internal openings of perianal tracts (Fig. 3). This is in agreement with a systemic review and meta-analysis by Maconi et al. [12], who reported sensitivity of 90.6% in detection of the internal openings of perianal tracts as well as Domkundwar et al. [13], who confirmed a sensitivity of 90–95% in identification of the site of the internal openings. On the other hand, Fateh SM [9] showed relatively lower overall accuracy of TPUS in detection of internal openings was 82%, with sensitivity of 85%.
Concerning the detection of perianal abscesses, a patient was diagnosed with a scrotal abscess by TPUS and was urgently drained by the surgeon. MRI images revealed the expected residual scrotal oedema (Fig. 4). TPUS failed to detect two (2/30, 6.7%) cases with abscesses. In the first missed case, MRI revealed a high left obturator externus abscess cavity; that is because TPUS has a limited penetration capability to see deep pelvic pathologies (Fig. 5). In the second missed case, the patient was in pain, and the radiologist could not proceed in the TPUS examination
. In our study, the overall accuracy of TPUS in detection of abscesses was 93.33% with specificity of 100%, which agreed with Mallouhi et al. [14] who declared specificity of 94–100% in visualisation of perianal abscesses. Our study showed that TPUS had PPV of 100% in detection of perianal abscesses, while Maconi et al. [12] showed PPV of 88.4%.
Regarding horseshoe collections, TPUS showed sensitivity, specificity and accuracy of 100%. This emphasises the ability of TPUS to detect horseshoe collections, which can change the surgical plan (Fig. 6). On the other hand, Nevler et al. [11] declared that two out of 27 patients had horseshoe collections, but TPUS failed to diagnose both of them.
Concerning detection of side branches of perianal tracts (Fig. 6), TPUS was able to detect the presence of side branches in (2/30, 6.7%) patients, comparable with Nevler et al. [11] who identified (2/27, 7.4%) patients with side branches. In disagreement with MRI, TPUS declined the presence of side branches in two cases (2/30, 6.7%) of our patients (Fig. 2). TPUS showed sensitivity of 50.00%, specificity of 92.31% and accuracy of 86.67% in detection of side branches.
Considering the visualization of supralevator extension, according to Lavazza et al. [3], we defined the presence of supralevator extension by the site at which the perianal tract breaches the anorectal junction or above, corresponding to the site of puborectalis muscle. TPUS reported the presence of supralevator extension of perianal tracts in (3/30, 10%) patients, in contrast to MRI which reported the absence of breaching of the levator ani muscle although these perianal tracts were high (Fig. 2).
Regarding the classification of perianal inflammatory disorders in relation to the anal sphincter, our study showed that TPUS correctly classified 23/30 (76.7%) patients, comparable with Nevler et al. [11] who correctly classified 23/27 (85.2%) patients of perianal inflammatory disorders.
Our study has points of strength, the radiologist who performed TPUS examination was blinded to MRI findings, to ensure the possible highest accuracy of our results. The time interval between TPUS and MRI examinations was less than 2 weeks, to avoid the expected changes of the radiological findings in case of long time interval between both imaging modalities.
Our study has limitations. TPUS is an operator dependant technique. TPUS examination may be limited by patient’s pain.