Physiological Investigations

The primary aims of tests used in FI patients are to better elucidate the pathophysiology and address the treatment. This is particularly complex, not only due to the lack of comprehensive knowledge on pelvic floor morphology and physiology but also because of the wide variety of tests used, not always as standard procedures. This assessment must concern both function [mostly provided by anorectal manometry (ARM), rectal sensations investigation, and anorectal electrophysiology (AREP)] and structure [given by endoanal ultrasound (EAUS) and/or magnetic resonance imaging (MRI)] of all components, pelvic and extrapelvic, involved in the continence mechanisms. Due to the multifactorial nature of FI, no one test alone is sufficient to provide these two types of information, and an integration of investigations is needed. When FI occurs with diarrhea, other possible causes should be explored by endoscopy and stool tests. As well, when clinical examination suggests that FI could be secondary to metabolic, neurological, or neurosurgical disorders; trauma; bowel inflammation; irradiation; or psychiatric disturbances, specific investigations should be programmed.

Table 1. Physical examination of patients with fecal incontinence (FI)

Examinations

Signs

Perianal inspection

Skin excoriation/infection Perianal/perineal scars Patulous anus Perineal soiling Anal ectropion Hemorrhoidal prolapse Rectal prolapse Sphincter deficit Loss of perineal body Perineal descent Fistula

Palpation

Pinprick touch Resting tone Squeeze tone

Puborectalis at rest, squeezing, straining

Sphincter deficits

Perianal/perineal scars

Anal/rectal neoplasms

Intussusception

Rectocele

Endoscopy

Hemorrhoids Anal/rectal tumors Inflammatory bowel disease Solitary rectal ulcer

Neurological

Perianal sensation Anal reflex Mental status

Anorectal Manometry and Rectal Sensation

These procedures are usually performed in the same setting and include the evaluation of rectoanal reflexes and rectal compliance. Although they are the most frequently used diagnostic procedures in proctology, particularly in FI patients, they are carried out het-erogeneously because of wide technical variations in computer software, probes (water perfused or solid state; uni- or multichannel; difference in number, location, and shape of openings; difference in location and material of balloon), acquisition modality of pressures (pull through or stationary), and sensations (inflation of either air or water or using baro-stat). For these technical differences, it is not possible to standardize either examination or normal values. Therefore, it is advisable to establish procedure and normal values in each laboratory according to age-and gender-matched healthy subjects [7]. In a study by Simpson et al. [8], five different manometric procedures (water-perfused side hole, water-perfused end hole, microtransducer, microballoon, air-filled probe) were compared; no significant variations in anal pressures were found using standard manome-try techniques, whereas pressures recorded by the air-filled probe were lower.

In incontinent patients, both resting and squeeze pressures should be calculated (Fig. 1). The investigator should be very careful to evaluate not only the

Fig. 1a, b. Anorectal manometry. a Resting pressure profile and b squeeze pressure profile in a patient with fecal incontinence (FI) due to a lesion of both internal and external anal sphincters numeric value (i.e., mean or median) but also to consider pressure profiles, providing information on asymmetry in the anal canal [due to a limited lesion of the internal anal sphincter (IAS) or the external anal sphincter (EAS)] or decreased EAS endurance to muscle fatigue during prolonged squeeze. Based on a multichannel acquisition of resting-pressure profile, it is usually possible to visualize a "vector manometry" and identify segments of the anal canal with increased or decreased pressure (Fig. 2). Following the routine use of EAUS, clinical utility of vector manometry has progressively reduced [9], even if, more recently, an inverted vector manometry has been suggested, giving good correlations with EAUS and providing combined functional and anatomic information [10]. On the other hand, in a number of incontinent patients, resting and/or squeeze pressures could be normal, related to a nontraumatic pathophysiology of their incontinence. Although the rectoanal inhibitory reflex (RAIR) is routinely evoked (Fig. 3), its meaning in pathophysiological assessment of FI is not well established. With this test, the threshold of the reflex and the percentage of sphincter relaxation, as well as relaxation time and

Fig. 1a, b. Anorectal manometry. a Resting pressure profile and b squeeze pressure profile in a patient with fecal incontinence (FI) due to a lesion of both internal and external anal sphincters contraction time, can be calculated. Other reflexes (coughing) should be elicited to investigate the level of possible spinal cord lesions. Very important parameters to be investigated in FI patients are rectal sensations, commonly studied by inflation of air in a rectal balloon to elicit threshold and urge sensations, and maximum tolerated volume. It seems that other modalities using either electrical or thermal stimulation cannot be standardized at this time [9].

Altered values can be found in FI patients with metabolic or neurological diseases or following bowel irradiation, as well as in "idiopathic" FI; however, in other incontinent patients, rectal sensation values could be within normal range. Indeed, either a normosensitive, hypersensitive, or hyposensitive rectum can be found in FI. Despite these different patterns, rectal sensation assessment should be regarded as one of the most useful parameters. In comparison with baseline values, variations in rectal sensation measured under treatment can be of help in the evaluation of therapeutic effectiveness. Rectal compliance is assessed by progressive inflation (with air or water, manually or with barostat) of a rectal balloon and registration of rectal pressure; it is defined

Fig. 2a, b. Vector manometry in a patient with fecal incontinence (FI) due to lesion of middle-lower internal anal sphincter, a "standard" vector, b "inverted" vector

Fig. 2a, b. Vector manometry in a patient with fecal incontinence (FI) due to lesion of middle-lower internal anal sphincter, a "standard" vector, b "inverted" vector

Rectoanal Inhibitory Reflex
Fig. 3. Rectoanal inhibitory reflex (RAIR). R relaxation time, C contraction time

by the ratio of rectal capacity to gradient pressure. Compliance reduction may cause rectal urgency and frequent defecation and is usually found in inflamed rectum (irritable bowel syndrome, ulcerative colitis, radiation injury), diabetes, or following low spinal cord lesions. Compliance may be increased in higher spinal cord lesions.

Endoanal Ultrasound

Specifically designed ultrasound probes and software are available to investigate the anal canal and rectum with EAUS. The most useful are those including radial probes with a full 360° field of view and a frequency range between 5 and 16 MHz. The probe outer diameter is 1.7 cm or less to minimize any anatomical distortion. EAUS is usually performed with the patient in left lateral decubitus position. During the examination, the probe is inserted into the anal canal reaching the puborectalis sling showing the U-shaped aspect. From this level, a manual or mechanical pull-through examination is performed evaluating the distinct layers and structures of the anal canal: submucosa, IAS, longitudinal sphincter, EAS, puborectalis, anococcygeal ligament, puboanalis muscle, and perineal body (Fig. 4). By convention, when an axial view is visualized, the anterior edge of the anal canal should be shown on the screen at 12 o'clock, the left lateral at 3 o'clock, the posterior at 6 o'clock, and the right lateral at 9 o'clock. However, a more recent EAUS technique allows three-dimensional imaging (3D-EAUS): the 3D structure

Bidimensional

Fig. 4a-c. Bidimensional endoanal ultrasound (EAUS): normal aspect of a upper, b middle, and c lower third of the anal canal obtained is the result of numerous axial, rapidly acquired, two-dimensional (2D) slices. Immediately after the examination and acquisition of these slices, the operator is able to navigate inside the 3D structure observing the anal canal not only in the axial but also in longitudinal and oblique views (Fig. 5). An area or volume can be calculated if deemed useful. Sphincter lesion appears as an hypoechoic area involving a circumferential segment of the IAS, EAS, or both (Fig. 6). EAUS is also particularly useful in differentiating FI patients with and without sphincter tears. Clinical utility of 3D-EAUS measurement of the anal sphincter complex in FI patients is under investigation [11]. Moreover, a "surface render mode" application is available in the most recently implemented ultrasonographic systems for EAUS (i.e., B-K

Fig. 4a-c. Bidimensional endoanal ultrasound (EAUS): normal aspect of a upper, b middle, and c lower third of the anal canal

Medical Hardware, equipped with 2050 endoprobe). This image processing allows changing the depth information of 3D data volume to "see the content inside a box" and offers accuracy in localizing sphincter tears.

Anorectal Electrophysiology

AREP includes a few tests directed to patients already investigated with history and physical assessment and other procedures (mainly ARM and ultrasound) in whom pelvic muscular and/or nervous functions seem to be altered. These tests, used to study the anorectum, have been derived from myographic and nerve conduction examinations performed in other

Fig. 5. Tridimensional endoanal ultrasound (EAUS): normal aspect in a longitudinal view parts of the body. Since the mid-1980s, an evolution of instruments, techniques of examination, and indications has been registered. Electrophysiological studies are usually carried out with a neuromyograph system equipped with software dedicated to anorec-tal physiology to evaluate electrical muscle activity and nerve functionality. In performing such tests, either a recording function or an electrostimulating function or both can be requested. The neuromyo-graph instrument has to be connected to dedicated cables and electrodes. A ground electrode soaked in normal saline is placed around the thigh. The most preferred patient position is left lateral.

The purpose of electromyography (EMG) is to investigate the electrical activity of the EAS and the other striated pelvic floor muscles at rest and during squeezing and straining. Muscle denervation or reinnervation could be found in incontinent patients.

Fig. 5. Tridimensional endoanal ultrasound (EAUS): normal aspect in a longitudinal view

Over time, four different types of electrodes have been developed: concentric needle, monopolar wire, single fiber, and surface. The concentric needle electrode consists of a thin needle (0.1 mm in diameter) covered by an insulating resin, which is able to uptake electrical activity of the small area of the EAS or puborectalis where it has been inserted under the guide of digital exploration. This needle is unable to record single muscle fiber action potentials; recordings from the four anal canal quadrants should be obtained. This procedure is quite uncomfortable for the patient, and even if multiple recording samples are taken, the mapping obtained is considered far from sufficient to delineate accurately the area of normal and abnormal muscle. The monopolar wire should reduce discomfort and avoid the electrode sliding because it is kept in site by a small hook placed at the electrode tip. The single-fiber electrode is thinner than the monopolar wire and is able to record individual motor-unit potentials. An appropriate amplification of the signals recorded is necessary. Also, fiber density can be calculated based on 20 different recordings from each anal hemisphere. Evaluation with single-fiber electrode is more accurate than the two electrodes previously described but remains uncomfortable. Surface electrodes, mounted on an endoanal plug or a small external adhesive plaque, are able to record gross muscle activity but unable to delimit areas of functional deficit. They are more useful to study paradoxical contraction of stri ated muscles than to evaluate sphincter damage in incontinent patients. Small polyphasic motor unit potentials (MUPs) may be identified when myopathic damage has occurred, whereas large polyphasic MUPs are found in neurogenic damage; also, a mixed pattern can be found. This test should be used when a neuro-genic sphincter weakness is suspected and to distinguish selectively disorders of EAS and puborectalis.

Mucosal sensation can be evaluated with electros-timulation not only in the rectum (as with ARM) but also in the anal canal using a bipolar ring electrode (containing two platinum wires 1-cm apart) mounted on a Foley catheter. An appropriate setting of stimulus duration and rate must be done before starting the examination. During this test, the electrode is inserted into the anus first. From zero, the current amplitude is slowly increased until the patient feels a buzzing or tingling sensation in the anus. At least three measurements need to be taken, choosing the lower threshold value for the report. A similar procedure is used for mucosal sensation analysis in the rectum. Rectal ampulla must be reached by the electrode; under slowly increasing current (parameter setting is different compared with that used for anal sensation test), three values should be obtained, taking the lowest as the rectal threshold sensation to be reported.

Pudendal nerve terminal motor latency (PNTML) is measured, allowing evaluation of the pelvic floor neuromuscular integrity (Fig. 7). A disposable St.

Loose Pelvic Floor Rectal Prolapse Gifs

Fig. 7. Normal pudendal nerve terminal motor latency (PNTML)

Mark's pudendal electrode is used, mounted onto the volar side of the examiner's gloved index finger. The index finger is inserted into the rectum, reaching with the fingertip the course of each pudendal nerve and laying with the proximal finger phalanx within the anal canal. During this test, both electros-timulation and recording function have to be activated. Four cables run within the electrode, conveying stimuli (0.1- or 0.2-ms duration, 1-s. interval, not exceeding 15 mA) from the machine to the fingertip (to the anode and cathode) to stimulate the puden-dal nerve fibers, and from the fingertip to the machine to record the striated muscle response, which is visualized on the screen. The latency (expressed in milliseconds) from the onset of the stimulus to the first deflection of the response is calculated for each pudendal nerve (n.v.: 2.0±0.2 ms). Because only the fastest conducting fibers are elicited during this test, it is possible to find a normal PNTML value in the presence of pudendal neuropathy, sparing a small amount of conducting fibers. Imprecise reproducibility and uncertain sensitivity and specificity are other limits of PNTML.

Evoked potentials can be obtained by stimulating the cortex or sacral roots to assess the central and peripheral motor (MEPs) and somatosensory (SEPs) pathways. Either electrical or magnetic stimulation can be used, the latter having the advantage of being painless and able to stimulate deep nervous structures. Both MEPs and SEPs allow the evaluation of conduction time of the stimulus (i.e., latency) and excitability of the intracortical circuit. Sacral MEPs have been proposed to replace PNTML [12], although the technical artefacts rate (up to 25%) is relevant [13-15]. These have been attributed also to vicinity of recording electrodes to the magnetic field, and use of an intrarectal ground electrode has been proposed to minimize artefacts [16]. Evaluation of SEPs can be performed by application of stimulus to the rectum, anal canal, anal verge, penis, or clitoris; this test could be helpful in assessing sensory fiber lesions, particularly in cases of perineal deficits. [17-19].

AREP could also include quantification of electrical or thermal sensory thresholds (QSTs) within the anal canal, sacral anal reflex (SAR) latency measurement in response to pudendal nerve or perianal stimulation, and perianal recording of sympathetic skin responses (SSRs) [19]. Integration between different tests can allow a reliable assessment of neuropathy. Lefaucheur [19] suggests that "needle EMG signs of sphincter denervation or prolonged TML give evidence for anal motor nerve lesion; SEP/QST or SSR abnormalities can suggest sensory or autonomic neuropathy; and in the absence of peripheral nerve disorder, MEPs, SEPs, SSRs, and SARs can assist in demonstrating and localizing spinal or supraspinal disease".

As mentioned above, indications for AREP are usually decided on the basis of a patient's history and physical assessment if pelvic muscular and/or nervous disorders are hypothesized; moreover, data from other diagnostic procedures (mainly ARM and ultrasound) should confirm the opportunity to submit the patient to the AREP.

In patients with sphincter lesion, no electrical activity may be found in case of wide, complete replacement of normal muscular tissue with scar, or, more frequently, polyphasic potentials as signs of a reinnervation process. Polyphasic potentials do present multiple spikes of muscle activity, prolonged in duration, and an increased fiber density. In evaluating sphincter injury, EAUS has higher sensitivity and specificity compared with EMG in mapping the lesion; however, only EMG can assess neuromuscular integrity. In this view, these two procedures are complementary to each other.

Evaluation of anal mucosal electrosensitivity could have a clinical relevance in a few clinical conditions. In neurogenic incontinence, a wide spectrum of findings can be observed, probably related to the degree of pudendal neuropathy. Also, rectal sensation measurements by electrophysiological study are meaningful. In incontinent patients with sphincter lesion(s) only, mucosal electrosensitivity could be normal. In those with neurogenic incontinence, there could be a wide variability of findings. As concerning manometric rectal sensation measurement, its meaning has to be intensively interpreted and correlated to results from other tests.

Alterations of PNTML are identified in relation to patient's age, being more frequent in older subjects. In a large number of patients with FI (with or without urinary incontinence) and rectal prolapse, the PNTML is abnormally prolonged. PNTML levels are thought to have a predicting value in patients undergoing treatment, but this assumption remains controversial.

Defecography and Magnetic Resonance

Defecography is able to assess pelvic floor physiology, recording motions at rest and during squeezing, straining, and coughing. The anorectal angle (ARA) should be calculated. A perineal descent is frequently found in incontinent patients. Moreover, rectorectal intussusception, rectocele, ente-rocele, or sigmoidocele may also be diagnosed; pelvic muscle dyssynergia needs to be adequately evaluated because it can cause continence disturbances [20].

MRI of anal sphincters has been evaluated using phased-array coils, but an endoanal coil has been preferred in studying FI patients [21] because of a superior accuracy in delimitating the EAS and sphincter defect; these should be the major advantages of MRI when compared with EAUS. However, controversy exists about preference toward endoanal coil [22]. EAS atrophy is more adequately visualized by MRI than by EAUS, as sphincter thinning occurs due to a decreased amount of muscle tissue and replacement with fat [23]. However, more recently, it has been reported that external phasedarray MRI is comparable with endoanal MRI in depicting EAS atrophy [24]. Endoanal MRI and 3D-EAUS have a comparable accuracy in detecting atrophy and defects of the EAS, even if there is a substantial difference in grading of external anal sphincter atrophy [25]. On the other hand, idiopath-ic IAS degeneration, or IAS atrophy, is better investigated with EAUS. Terra and Stoker [26], in reviewing imaging techniques in FI, concluded that both external phased-array MRI and 3D-EAUS are "valuable tools in the diagnostic work up of faecal incontinence. Decisions about the preferred technique will mainly be determined by availability and local expertise".

More recently, use of MRI defecography suggested [27] to be included in the diagnostic workup of FI patients to detect previously missed functional alterations of anterior, middle, or posterior pelvic compartments. This examination should improve diagnosis of rectocele and internal prolapse when compared with clinical evaluation and allow the choice of a more adequate treatment.

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