*Jacek Piłat1, Sławomir Rudzki1, Jacek Bicki2, Wojciech Dąbrowski3
Progress in diagnostic imaging of anal inflammatory diseases
Postępy w diagnostyce obrazowej chorób zapalnych odbytu
11st Chair and Department of General Surgery, Transplantation and Nutritional Therapy, Medical University of Lublin
2Institute of Medical Sciences of the Faculty of Medicine and Health Sciences, Jan Kochanowski University in Kielce
3Chair and 1st Department of Anaesthesiology and Intensive Therapy, Medical University of Lublin
Autorzy przedstawiają zagadnienia z zakresu diagnostyki najczęściej spotykanych chorób zapalnych odbytu. W sposób szczególny zajmują się przetokami i ropniami odbytu. Przedstawiają różne metody diagnostyczne: począwszy od podstawowego badania proktologicznego poprzez metody instrumentalne. Oceniają przydatność, wady i ograniczenia poszczególnych metod. Najwyższą ocenę z przedstawionych metod diagnostycznych uzyskały dwa badania, tj. rezonans magnetyczny i badanie endosonograficzne w opcji 3D, wsparte użyciem opcji render mode lub wody utlenionej jako środka kontrastowego. Oba badania w pewnym sensie są porównywalne, jeżeli chodzi o choroby zapalne odbytu. W przypadku badania endosonograficznego zaletami są: niski koszt, powtarzalność i dostępność. Do wad rezonansu magnetycznego należą: wysoka cena badania, mała dostępność i ewentualna klaustrofobia pacjenta lub obecność metalowych implantów. Jednak niezaprzeczalną zaletą badania metodą rezonansu magnetycznego jest możliwość oceny przetok lub ropni odbytu zlokalizowanych wysoko, powyżej mięśni dźwigaczy. W ocenie zmian głęboko położonych przewaga rezonansu magnetycznego wynika z krótszego ogniska sondy endosonograficznej. Wysoka częstotliwość sondy daje dobrą jakość obrazu, ale okupiona jest krótszą penetracją w głąb promieni ultrasonograficznych. Użycie opcji render mode lub kontrastu – wody utlenionej – stawia badanie endosonograficzne w jednym rzędzie z rezonansem magnetycznym w diagnostyce płycej położonych, częściej występujących przetok i ropni. Mając na uwadze niższe koszty i powtarzalność badania endosonograficznego, jest ono cennym nowoczesnym instrumentem w diagnostyce zmian zapalnych odbytu.
The authors present issues related to the diagnosis of the most common inflammatory diseases of the anus. They deal with anal fistulas and abscesses in a special way. They present various diagnostic methods: from basic proctological examination to instrumental methods. They asses the usefulness, disadvantages and limitations of individual methods. The highest assessment of the presented diagnostic methods was obtained by two tests, i.e. magnetic resonance imaging and endosonographic examination in the 3D option, supported by the use of the render mode option or hydrogen peroxide as a contrast agent. In a sense, both examinations are comparable when it comes to inflammatory diseases of the anus. For endosonographic examination, the advantage is low cost, repeatability and availability. The disadvantage of magnetic resonance imaging is the high price of the test, the low availability and possible claustrophobia of the patient or the presence of metal implants. However, the undeniable advantage of magnetic resonance imaging is the ability to assess anal fistulas or abscesses located high above the levator muscles. In the assessment of deeply located lesions, the advantage of magnetic resonance results from the shorter focus of the endosonographic probe. The high frequency of the probe gives good image quality, but it is paid for the shorter penetration of the ultrasound rays. The use of the render mode or contrast – hydrogen peroxide option puts the endosonographic examination in a one row with magnetic resonance imaging in the diagnosis of the most frequent occurring fistulas and abscesses. Considering lower costs, repeatability of the endosonographic examination it is a valuable modern instrument in the diagnosis of inflammatory lesions of the anus.
Inflammatory diseases of the anus are one of most common causes of patients’ appointments at surgical clinics and wards. Inflammatory diseases include abscess, fistula, anal fissure, and proctitis. They are manifested by various signs and symptoms, mainly local ones (pain, redness, oedema, bleeding, bowel movement disorders, discharge of purulent or bloody contents within the anus) and sometimes general ones, i.e. inflammatory, e.g. for highly located abscesses. Appropriate diagnostics is important for the correct diagnosis and optimization of therapy.
The most common inflammatory diseases of the anus are anal fissures, fistulas and abscesses, which, besides basic proctological examination, often need additional imaging tests. The result of such an examination is to determine the course of the fistula canal or the abscess location (relation to sphincters), or to determine internal opening location. Anal abscesses are generally clinically manifested and the diagnosis does not raise any doubts. However, there are hourglass-shaped abscesses or abscesses located high above the levator ani muscles, which may not demonstrate any symptoms in the anal area, but general symptoms only. In these cases, extended diagnostics with additional tests is very important for the appropriate treatment. Pain in the anus area of unclear etiology is also an indication for expanded diagnosis, as basic proctological examination is not sufficient (fig. 1).
Fig. 1. A small abscess with evident air, deeply located between the pubic-rectal muscle brachium; clinically silent abscess between the arrows, with a size of 8.4 x 6.8 x 5.6 mm
Patients often visit medical facilities due to complications or recurrence of proctological diseases. Proper diagnosis and evaluation of already occurring damages caused by the disease and the treatment process affect the therapy and final result. Encopresis may be caused by systemic diseases, aging, but also by sphincter failure due to e.g. past procedures, anal canal injury.
Diagnosis of proctological diseases is based on a history and physical examination as well as additional tests. In addition to examining the perineum and perianal area and finger examination of the anus, the following examinations may be carried out: anoscopy or rectoscopy, transrectal or perrotal endosonography, defecography, balloon excretion test, fistulography, rectal-anal manometry, CT and magnetic MRI with or without rectal coil. All of these examinations have their advantages and limitations, the selection depends on the history and initial proctological examination, and the availability of the diagnostic method.
An anal fistula is a granulation tissue surrounding canal that connects the internal fistula opening located in the anal canal with the external opening – most commonly located on the skin around the anus area. According to the cryptic theory, infection that begins in Herman’s anal glands and spreads to the perianal area is the cause of abscesses and fistulas in this area. Acute infection forms an abscess, and a fistula is its chronic form (1, 2).
Other less frequent etiological factors include: inflammatory diseases (Crohn’s disease in particular, where the internal opening is often located deeper than in the perianal crypts), infection spreading from anal fissure, coccygeal cysts, tumors, foreign bodies, lymphomas, tuberculosis, HIV infection, post procedure complications in this area (3, 4).
The purpose of fistula diagnostics is to properly classify, i.e. describe, the fistula anatomical course. Currently, the Parks classification is the most commonly used one. This classification considers location of the internal opening and the course of the fistula canal in relation to the external sphincter muscle. The following fistulas are distinguished: submucous, inter-sphincteric, trans-sphincteric, supra-sphincteric and extra-sphincteric (5).
It is also important to determine whether the fistula transits the anterior or posterior or lateral part of the anal canal. This is particularly important in women where the anterior – perineal part of the anal canal has a shorter external sphincter and therefore fistula surgery in the anterior part is more exposed to complication in the form of sphincter failure (6, 7).
Goodsall and Miles classification is another classification that divides fistulas into: complete, i.e. of two openings – external opening on the skin around the anus, and internal opening to the lumen of the gastrointestinal tract, and incomplete, i.e. externally blind fistula, i.e. no external opening or internally blind fistula, i.e. without visible internal opening (8).
Many additional tests may be used in the diagnostics of anal fistulas, however there are practitioners who believe that basic physical examination is sufficient. This particularly refers to primary fistulas, untreated and uncomplicated. In other cases, additional tests should be performed (9).
The Salomon Goodsall’s rule is the first clue, although not very precise, as to the location of the internal opening when inspecting the perianal area. It divides the anus by means of a horizontal line to anterior and posterior parts. The location of the external opening in the anterior half suggests a suspected fistula with a straight canal going to the anterior crypt. If the external opening is in the posterior half, or more than 3 cm from the anus edge in the anterior half, then the fistula canal most likely goes to the posterior crypt – caudal. This rule works in circa. 80% of cases of fistulas with an internal opening in the posterior half, and only in circa. 50% of cases with an opening in the anterior half of a divided anus (10).
The most frequently performed additional tests in the diagnostics of anal fistulas include (11):
1. X-ray fistulography – rarely used currently due to the need to irradiate a patient and low accuracy, i.e. up to 25% in identification of internal opening in the appropriate crypt. Locating the internal opening in high extrasphincteric fistulas is its advantage – this allows, for example, for the contrast to enter the sigmoid diverticulum (12, 13).
2. Transanal and transrectal ultrasonography (TAUS – transanal ultrasound and TRUS – transrectal ultrasound) – used due to high accuracy and examination specificity as well as low cost and repeatability. The test is performed in the Sims position (i.e. on the left side), a high-frequency ultrasound probe (from 9 to 16 MHz) is introduced, ensuring a 360-degree image – which allows for entire anus view on the image. When examining the rectal ampulla (a water balloon should be used to ensure conduction of the ultrasound beam), a layered structure of a rectal wall may be viewed and analyzed and compared with an image of the entire cross-section (fig. 2a, b).
Fig. 2a, b. (a) Anal canal examination (hypoechogenic internal sphincter and surrounding external sphincter showing mixed echogenicity); (b) rectal ampulla examination (visible layered intestinal wall structure)
3D option of this ultrasound examination allows for scanning the anal canal or rectal ampulla up to a length of 65 mm and viewing the scanned area in each of three planes. This is helpful for fistula canal imaging and accurate assessment of its course in relation to the surrounding structures. Assessment in the frontal or sagittal plane helps measure the length of the anal canal and thus determine the distance from the external edge of the anal canal to the internal opening, which is very important for selection of fistula and abscess therapy (fig. 3a, b).
Fig. 3a, b. Posterior intersphincteric abscess: (a) transverse plane: posterior right abscess with visible defect of IAS internal anal sphincter (between white caves); (b) sagittal plane: visible internal opening 15 mm from the external edge of the anal canal at the length of the anal canal 40 mm (EAS – external anal sphincter)
To improve the diagnostic sensitivity and specificity, render mode options may be used additionally, i.e. digital improvement of particular voxels (individual images), which results in better visualization of image details with regard to small differences in the echogenicity of the examined elements. There are four variable parameters of the render mode option (opacity, luminance, thickness and filter) used to achieve the expected effect. By means of the render mode option, it is easier to distinguish the external anal sphincter from the pubic-rectal muscle. This helps view an abscess or internal opening of the fistula (14, 15) (fig. 4a-c).
Fig. 4a-c. Anal canal images: (a) TAUS (transanal ultrasonography); (b) RMTAUS (render mode transanal ultrasonography), high filter values, low values: luminance, thickness and opacity); (c) RMTAUS high luminance values, low values: filter, thickness and opacity
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