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Role of Transcutaneous Perianal Ultrasound in Evaluation of Fistula in Ano
Shilpa Domkundwar* , Girish D Bakhshi+, Waqar A Ansari++, Atul B Shinagare**, Benazir Palekar+++, Siddharth Sarangi+++ |
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Abstract
Aims and Objectives : To evaluate role of transcutaneous perianal ultrasound (TPUS) in evaluation of fistula in ano and to assess its possible role as a substitute to MRI and endoanal ultrasound.
Material and Methods : TPUS was performed in 15 patients of fistula in ano using Toshiba Eccocee, Justvision, Nemio (Japan) with a 3.5MHz sector probe, 7-11MHz linear probe and 5-7MHz endocavitatory probe. Patients were followed up clinically and at surgery to assess the accuracy of TPUS.
Results : TPUS reliably and adequately demonstrated majority of fistulas and abscesses. It cannot adequately evaluate suprasphincteric type of fistulas, which are the least common. It acts as a good and cheap modality in the evaluation of patients of fistula in ano and also helps in follow up of these patients. It can also be used as a screening procedure to select patients who need MRI.
Conclusion : TPUS has a potential to obviate need of MR evaluation for fistula in ano in a majority of patients. |
Introduction
Fistula in ano dates to antiquity.
Hippocrates has made references to this entity. Louis XIV was treated for fistula in ano in 18th century. In a government hospital in India, where a large majority of patients are from lower socio-economic class and with poor personal hygiene fistula in ano is a common affliction. It has propensity for chronicity and needs frequent follow-up. In view of high cost and scarcity of MRI or CT and of the discomfort associated with endoanal ultrasound, there seems a need of simpler, cheaper and easily available method which can adequately evaluate perianal fistulas and abscesses. Transcutaneous Perianal Ultrasound (TPUS) holds such a promise.
Aims and Objectives
1. To study the role of TPUS in evaluation of fistula in ano.
2. To assess the role of TPUS as an initial screening method to select patients needing MRI.
3. To evaluate its role in follow up.
Material and Methods
Fifteen patients with a long term history of discharging sinuses were studied by TPUS and followed up in surgery department till surgical cure or discharge and follow-up. One female and 14 male patients were studied. Patients were in age range from 24 to 46 years.
No specific patient preparation was used. TPUS was performed under hygienic conditions in lithotomy position. Left lateral position was used wherever necessary.
Patients were scanned using Toshiba Eccocee, Justvision or Nemio machines as per availability in the department, with 3.5-5MHz sector probe, 7-11MHz linear probe and 5-7MHz transvaginal probe.
Examination started with visual inspection of perianal region with regards to number and position of sinus openings, their distance from anus, whether or not discharging and palpation of area of induration and tenderness. These findings help guide the study. For example, deep postanal or ischiorectal extension is suggested by lateral or posterior induration.
3.5MHz sector probe was used for initial screening in sagittal, and parasagittal planes. This gives better orientation of anatomy as regards to position of bladder, prostate, rectum, etc. Then high resolution linear and endocavitatory probe was used percutaneously. It has the advantage of better access in the cleavage of buttocks due to its small head. It took some experience to get proper orientation of anatomy using this probe. 5 – 7.5 MHz probe allows imaging of superficial and deeper structures using the same probe and position.
The path, direction, extent, diameter and internal branching and openings of tracts were mentioned in lithotomy position. Presence, location and extent of any collection/abscess was also noted.
Midsagittal view was used to visualize the pelvic diaphragm and its relation to the tract or collection. Patient was asked to bear down in order to see the movement of pelvic diaphragm.
Findings of TPUS were confirmed with intraoperative findings in twelve cases. Two patients were followed up clinically till tracts closed. There was one case of gluteal abscess.
Results
Fistulae and sinus tracts are seen as hypo to anaechoic tracts, usually 3 to 6 mm in diameter. In some of them, hyperechoic specks were seen representing air, movement of which could be seen. Air in fistula tract is a good sign of an active fistula. In some cases the movement also helps to find the internal opening of the tract. Fibrous tracts are seen as more well defined, echogenic structures. Inflamed tracts had fuzzy margins.
Some showed presence of a collection or abscess. Well formed abscesses were seen as hypo to anaechoic collections. Depending on the chronicity and localisation, walls of abscesses ranged from ill defined to well defined. Incompletely liquefied areas appeared more heterogenous. Organised chronic abscesses were more heterogenous and echogenic, but showed better defined margins. Occasionally the internal opening into the anal canal could be demonstrated. Out of 15 cases, single internal opening was found in 7 cases, multiple internal openings were found in 4 cases. Two cases showed no internal openings on TPUS, out of which one was blind and in one case, internal opening was detected on surgery.
Ten patients had single external opening and four others had multiple external openings. Out of the 10 cases with single external opening 4 had complex tracts within. One patient had an internal collection and a tract with no external opening. Of all the cases 9 cases had internal collections, of which 3 had multiple collections (Table 1). One patient had a gluteal abscess with no internal connections. One patient had an extrasphincteric collection.
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Fig. 1 : Anatomy of perineal region as seen on TPUS. |
Fig. 3 : Looser zones and micro fractures, Dec. 2003. |
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Fig. 1 : Anatomy of perineal region as seen on TPUS. |
Fig. 3 : Looser zones and micro fractures, Dec. 2003. |
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| Fig. 1 : Anatomy of perineal region as seen on TPUS. |
Fig. 3 : Looser zones and micro fractures, Dec. 2003. |
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Discussion
Fistula in ano is a hollow tract lined with granulation tissue with one opening in anal canal and outer secondary opening in perianal region. Multiple secondary tracts are known to occur.
Anal canal glands situated at the dentate line afford the path for the infecting organisms to reach the intermuscular spaces leading to anorectal abscess, which in turn leads to fistula formation. Other causes include trauma, Crohn’s disease, anal fissures, malignancies, radiation therapy, tuberculosis, actinomycosis, chlamydia, etc.
The prevalence rate is 8.6 cases per 100,000 population. The prevalence in men is 12.3 cases per 100,000 population. In women, it is 5.6 cases per 100,000 population. The male-to-female ratio is 1.8:1. The mean age of patients is 38.3 years.1
Clinical presentation:
- Perianal discharging sinuses
- Pain, swelling
- Skin excoriation
- Diarrhoea, altered bowel habits
- Weight loss
Predisposing factors for recurrence:
- Inflammatory bowel disease
- Diverticulosis
- Tuberculosis
- Steroid therapy
- HIV infection
Differential Diagnosis includes:
- Bartholin gland abscess in females
- Pilonidal disease
- Infected inclusion cysts
But these do not communicate with the anal canal.
Anatomy
In order to understand the classification system of fistulous disease, one must understand the pelvic floor and sphincter anatomy.
The external sphincter is made up of striated muscle arising from anococcygeal raphe. It has 3 components- submucosal, superficial, and deep muscle. Its deep segment is continuous with the puborectalis muscle and forms the anorectal ring, which is palpable upon digital examination.
The Sphincter ani internus is a muscular ring which surrounds about 2.5 cm of the anal canal. It is a smooth muscle which is an extension of the circular muscle of the rectum. Its lower border is about 6 mm. from the orifice of the anus.
Goodsall’s Rule
Fistulae with an external opening anterior to a plane passing transversely through the centre of the anus will follow a straight radial course to the dentate line. Fistulae with their openings posterior to this line will follow a curved course to the posterior midline. Exceptions to this rule are external openings more than 3 cm from the anal verge. These almost always originate as a primary or secondary tract from the posterior midline, consistent with a previous horseshoe abscess.
Parks classification: 4 types of fistula-in-ano-
l Intersphincteric: These account for seventy per cent of all anal fistulae. They course via internal sphincter to the intersphincteric space and then to the perineum. Variations like absence of perineal opening, high blind tract, high tract to lower rectum or pelvis are seen.
l Transsphincteric: this type extends through internal and external sphincters into the ischiorectal fossa and then to the perineum and accounts for 25% of all anal fistulae.
l Suprasphincteric: Via intersphincteric space superiorly to above puborectalis muscle into ischiorectal fossa and then to perineum. Five per cent of all anal fistulae
l Extrasphincteric: Extend from perianal skin through levator ani muscles to the rectal wall completely outside sphincter mechanism. One per cent of all anal fistulae.
Parks Classification doesnot contain subcutaneous variety which is secondary to fissures or anorectal procedures such as sphincterectomy.
Currently the imaging evaluation of fistula in ano rests on:
Fistulography: it is a simple procedure but accuracy rate is only 20-50%. In addition, it may not show branching tracts, blocked tracts and internal openings and collections reliably.
Endoanal/endorectal ultrasound:
This study is done using 7 to 10 MHz transducer introduced into anal canal. It gives accurate and high resolution definition of muscular anatomy, thus being able to distinguish between intersphencteric and transsphincteric lesions. With a help from a water-filled balloon transducer, suprasphincteric extension may be evaluated. Internal openings are likely to be missed but it is still better than physical examination for this purpose. It does not allow imaging of gluteal region. It is uncomfortable for the patient and in our setup, many patients refuse to undergo this procedure. It is not routinely used for evaluation of fistula.
CT Scan:
CT scan is helpful for evaluation of perirectal inflammatory disease. But it is not reliable in delineating small fistulous tracts. Also, it does not delineate the muscular anatomy well and pelvic diaphragm can not be adequately evaluated.
MRI:
MRI shows 80-90% correlation with intraoperative findings in outlining primary and secondary tracts. It has also shown to reduce recurrence rates by providing information on otherwise unknown extensions. It is becoming the study of choice when evaluating complex fistulae.
Disadvantages of MRI:
- Lacks the definition of high resolution ultrasound
- Expensive
- Specialised equipment needed
- Time consuming
- Less feasible for follow-up on account of it being costly and time consuming.
- Real time correlation not possible.
Transcutaneous Perianal Ultrasound
Our study showed that TPUS has the potential to become the initial and most cost-effective investigation for fistula disease, which may alleviate the need for MRI in most patients.
Its advantages are:
1. Excellent detection rates of primary and secondary tracts, their course and extent, even in blocked tracts which are not evaluable by fistulography.
2. Levator ani and external sphincter are well evaluated. Muscle mobility can also be judged. Suprasphincteric type can be easily identified.
3. Good detection of perianal abscesses.
4. Air in fistula tract is a reliable sign of active fistula.
5. Can be performed in patients with anal stenosis (Endoanal ultrasound can not be performed in these patients).
6. Real time visualisation (CT, MRI lack this).
7. Multiplanar capability.
8. Can be used intraoperatively to delineate the tracts.
9. No specialised equipment needed. (Important consideration in our setup.)
10. Easily available
11. Cheap
12. Rapid evaluation
13. Easily reproducible
14. Easy to perform (though requires some experience to get oriented to anatomy)
15. Painless (as opposed to endoanal ultrasound)
16. Ideal tool for follow-up cases.
17. No patient preparation required.
We found following shortcomings of TPUS:
1. Assessment and differentiation between internal and external sphincter and intersphincteric collections was less satisfactory than endoanal ultrasound. But patients needing endoanal ultrasound can be identified, thus limiting the use of this modality to certain selected patients. Internal openings are not always adequately demonstrated.
2. Being operator dependent, orientation to anatomy may be difficult for surgeons initially. But we were able to reduce this problem by scanning the patients in presence of surgeon, which also helped in planning the surgery.
3. Difficulty in evaluating high type of fistulas.
Conclusion
At present, combination of MRI and Endoanal Ultrasound gives highest sensitivity. But considering above mentioned advantages and disadvantages of TPUS, we propose its use as a powerful screening modality, which can obviate the need of MRI in a majority of cases. It can be combined with Endoanal Ultrasound for better results and both these procedures can be performed in a single sitting. Together, these have the potential to reach the sensitivity of MRI and Endoanal Ultrasound combination. It can also help us select a small group of patients who need MRI, thus limiting the use of MRI. TPUS has its greatest advantage in being cheap, easily reproducible and an excellent modality for follow-up.
References
1. Jochen Wedemeyer, Timm Kirchhoff, Gernot Sellge, et al. Transcutaneous perianal sonography: A sensitive method for the detection of perianal inflammatory lesions in Crohn’s disease World J Gastroenterol 2004 October.
2. Bonatti H, Lugger P, Hechenleitner P et al. Transperineal Sonography In Anorectal Disorders Ultraschall Med 2004 Apr; 25 (2) : 111-5.
3. Gary S. Sudakoff, Francisco Quiroz, W. Dennis Foley. Sonography of Anorectal, Rectal, and Perirectal Abnormalities. AJR 2002; 179 : 131-6.
4. Stewart LK, Wilson SR. Transvaginal sonography of the anal sphincter: reliable, or not? Am J Roentgenol 1996; 173 (1) : 179.
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