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2. Reflex Testing and Pelvic Examination
Keywords
Lumbar plexusSacral plexusCoccygeal plexusPudendal nerveAbdominal reflexesCremasteric reflexAnocutaneous reflexClitoral-anal reflexBulbocavernosus reflexGuarding reflex2.1 The Somatic Component
Somatic, parasympathetic and sympathetic components innervate the organs contained in the pelvis. The clinical evaluation of the perineum sensitivity must pay particular attention to the fact that adjacent areas of skin surface (adjacent dermatomes such as L1–L2 and S2–S3) refer to metamers which are well distant at a spinal cord level: during development, in fact, the rotation of the lower limb causes this apparently unordered distribution [1].
The sensitivity evaluation of the perineal area is performed on the supine patient with his/her hip and knee bent, in order to explore the various areas which will be stimulated, usually with a cotton stick, to evaluate the exteroceptive tactile and pain sensibility, including visually.
The “touch” of the cotton stick aims to explore the urogenital and the anal triangle, which are both innervated by the pudendal nerve [2–5], with some thoracolumbar nerves overlapping with it in this area.
The anterior branches of the spinal nerves from T12 to L4 form the lumbar plexus, which has close relations with the posterior abdominal wall, running along the psoas muscle; the sympathetic afferents run in the upper hypogastric plexus, while the parasympathetic ones in the inferior hypogastric plexus.
Anterior cutaneous branches from T7 to T12 provide the somatic innervation of the abdominal wall; in particular, the area innervated by the iliohypogastric nerve includes the superior lateral skin portion of the buttock and comes up to the suprapubic skin.
Sensory innervation in the female perineum
Sensory innervation of the male perineum
The sacral plexus is formed by the roots L4–S4, emerges from the sacral foramen and moves sideways in close contact with the piriformis muscle, innervated by the first and second sacral nerves.
The inferior gluteal nerve (posterior branches of L4, L5 and S1) innervates the gluteus maximus muscle, passing below the piriformis muscle; the femoral cutaneous provides innervation to the anterolateral part of the perineum [6, 7].
There are some controversies about the constitution of the pudendal nerve trunk: it is usually described as originating from S2, S3 and S4; there are some observations which hypothesise a contribution also of the S1 root [8–10].
Running between the piriformis muscle and the coccygeal muscle, it enters the perineum through the small ischial foramen, and runs in the Alcock’s canal to then divide into its terminal branches. The pudendal nerve guarantees the sensitivity of the anterior and posterior perineum, conveying within itself afferent but also efferent somatic fibres, sympathetic and parasympathetic efferent fibres and visceral afferent fibres [2–5, 11, 12].
The dorsal nerve of the clitoris (in the female) and the dorsal penile nerve (in the male) run along the ischiopubic ramus and provide skin innervation to the clitoris or the penis; a second branch, the inferior rectal nerve, after having run through the Alcock’s canal reaches the perianal area, ensuring motor and sensory somatic innervation to the external anal sphincter, the anal canal and the adjacent cutaneous area [13–15]. The last branch, the perineal nerve, provides innervation of the cutaneous area corresponding to the perineal body; its deep component supplies the transverse muscles of the perineum, the bulbospongiosus muscle, the ischiocavernosus muscle and part of the external anal sphincter.
The coccygeal plexus is formed by a small branch descending from the IV sacral root, the V sacral root and the ventral coccygeal branch. The V sacral root exits the sacral hiatus, and crosses the coccygeal muscle to reach the perineum. The levator ani muscles and the coccygeal muscle, together with the sacrococcygeal articulation and the skin over the anococcygeal raphe, are innervated by the coccygeal plexus.
The sensory innervation of the anus and rectum ensures two functions: the rectal “sampling” and the detection of the degree of distension of the rectal walls in order to trigger the recto-anal inhibitory reflex (RAIR) for beginning the defecation or, on the contrary, the voluntary contraction of the muscle-sphincter complex to postpone it and the anal sensitivity [16, 17].
In the anorectal area, the afferent nerve impulses are conveyed by the pudendal nerve [18] by both myelinated and non-myelinated fibres [19].
2.2 The Sympathetic and Parasympathetic Components
The greater splanchnic nerve (from the sympathetic thoracolumbar fibres T5 to T9) connects with the celiac plexus and innervates the small intestine and the colon. The fibres from T10 and T11 form the minor splanchnic nerve which equally innervates, through the upper mesenteric plexus, the small intestine and the colon; the last splanchnic nerves originate from T12 and send fibres to the renal and ovarian plexuses [14, 20].
The lumbar splanchnic nerves, through the inferior mesenteric plexus, in part innervate the colon and through the rectal upper plexus the rectum, the anal canal and the internal anal sphincter; in the caudal area, it takes the name of superior hypogastric plexus (exclusively sympathetic plexus), which innervates the sigmoid, ureters and uterus. Each hypogastric nerve receives a component from the sacral splanchnic nerves and forms the pelvic plexus (inferior hypogastric plexus) with a sympathetic and parasympathetic double component, which innervates the bladder (bladder plexus), the uterus and vagina (uterovaginal plexus) and the rectum (rectal plexus).
The parasympathetic system has a sacral protrusion with fibres that originate from the cranial nerves with some components of the sacral spinal nerves. In contrast to the sympathetic neurons, preganglionic fibres contract synapses with the postganglionic fibres in the vicinity of the target organs. The abdominal-pelvic area is innervated mainly by the vagus nerve; the vagal fibres join sympathetic fibres in the upper and lower mesenteric and celiac plexuses and contract synapses with the postganglionic fibres in the enteric ganglia (in the Meissner and Auerbach plexuses) to innervate the small intestine, colon, kidneys and ureters. The sacral parasympathetic fibres (anterior branches of S2, S3 and S4) innervate the digestive tract and the urogenital organs through the pelvic plexus.
2.2.1 Clinical Evaluation of Reflexes
2.2.1.1 Surface or Exteroceptive Reflexes (Polysynaptic Reflexes)
The evaluation of reflexes allows the possibility of identifying the level of injury in the CNS during a general neurological examination. Put simply, all reflexes represent a sensorimotor arc with a single link between the afferent branch and the efferent one (monosynaptic reflex) or with one or more interposed neurons (polysynaptic reflex). They can be controlled by inhibitory and/or excitatory influences that reach the spinal level, originating from different areas of the CNS, which are therefore able, in the presence of any disease, to modify the reflex response. Superficial or exteroceptive reflexes are mediated by a polysynaptic arch, therefore substantially different from monosynaptic proprioceptive reflexes, since their processing takes place thanks to the intervention of interneurons also at a supraspinal level; the receptors consist of mechanoreceptors and nociceptors of the skin and mucosa, the afferent pathway of T cells with myelinated axons and the efferent pathway from the alpha motor neurons. In the case of exteroceptive reflexes, the stimulus and the response to the stimulus are shown in different organs or apparatuses, and different peripheral nerves or nerve roots represent the afferent pathway and the efferent pathway of the reflex; usually triggered by stimulating the skin with a “rubbing” movement (usually the stimulation is carried out with a rigid and rounded object, in this case, a wooden stick), these are evaluated as “present” or “absent”, considering that marked-side asymmetries must be considered as pathological.
The repeated attempt to trigger the reflex makes the response less evident and exhaustible.
Their abolition may be secondary to a lesion of the afferent nerves or the second motor neuron efferent and of all cases of interruption between the brain and spinal cord [21].
2.2.2 Abdominal Reflexes
Originally described by Rosenbach [22], it is recommended that they should be triggered initially by using the Wartenberg “pinwheel” [23]. Currently, it is suggested to cause the contraction of the abdominal muscles by stimulating the peri-umbilical skin with a blunt tip with a movement in the latero-medial direction towards the navel, performed bilaterally in the four abdominal quadrants, above and below the navel [24], with the patient in a supine position, relaxed, looking for reflexes at the end of an exhalation; the afferent nerve impulses are conveyed by the intercostal, ilioinguinal and iliohypogastric nerves [25].
The contraction generally determines the “displacement” of the navel itself towards the stimulated quadrant; it is, therefore, possible to trigger superior or epigastric reflexes (spinal segments T7–T9), medium reflexes (T9–T11) and inferior reflexes (T11–T12, overlapping with L1) [26].
They can be very lively in case of an anxious state or of a long-standing corticospinal lesion [27] and bilaterally absent in 15% of the population, in the elderly person, in the obese person and in the multipara. They are absent on one side in case of interruption of the reflex arc (shingles, abdominal surgery outcome, lesions of the second motor neuron), as well as in the case of an ipsi- or contralateral lesion of the cranial-spinal tract at the examined level. They can therefore assist in the diagnosis of thoracic spinal cord injuries [27].
An “inverse” response may rarely be triggered with a contraction of the contralateral muscles related to stimulation; they may be precociously absent in case of multiple sclerosis [28], a sign described by Ernst Adolf Gustav Gottfried von Strümpell in 1896.
They can be triggered instead in case of amyotrophic lateral sclerosis and of myasthenia gravis [26].
2.2.2.1 “Deep” Abdominal Reflexes
“Deep” abdominal reflexes have been described, triggered not by stimulating the skin of the abdomen, but by stretching the musculature itself, activating it with the hammer or Wartenberg pinwheel on the abdominal wall [29]. The absence of superficial ones in the presence of accentuated deep reflexes (dissociation between “deep” and “superficial” abdominal reflexes [30]) would suggest a bilateral lesion of the pyramidal tract above the T6 [31, 32].
2.2.3 The Cremasteric Reflex (in the Male)
Described by Monrad-Krohn and Kornfeldt in 1925, it is triggered by stimulating the afferent fibres of the ilioinguinal nerve in the medial area of the thigh and with the efferent motor response of the genital branch of the genitofemoral nerve [33]; the cremasteric muscle determines the elevation of the testis on the same side where the stimulation occurred.
Present after 2 years of age, the reflex cannot always be triggered even under normal conditions; it assesses the L1–L2 segment: it may be important in the diagnosis of lesions at the lumbar plexus, in diabetic neuropathy, lymphomas, autoimmune diseases and rarely Lyme disease or polyarteritis nodosa.
It can be absent in elderly persons or in the outcome of abdominal surgery for hernia or hydrocele or in lesions of the L1–L2 cranial contralateral pyramidal tract or L1–L2 spinal lesions [34–36].
The cremasteric reflex is a somatic motor reflex; it has also been described as the “dartos reflex” [33] or “scrotal reflex”, an autonomic reflex, but clinically similar to the cremasteric reflex since the afferent and efferent arcs of the reflexes differ only in the “dartos reflex for the sympathetic component” [37].
The dartos muscle is a cutaneous smooth muscle which adheres tightly to the deep layer of the scrotal bag skin, of which it is a tunica. Similarly to the cremasteric muscle, it receives fibres from the genitofemoral nerve, in particular also from a contingent of fibres of the sympathetic nervous system, which originate in the thoracolumbar cord (T12-L1-L2). This component is responsible for the “corrugation” of the scrotal skin, which manifests itself with a slightly higher latency than the testicular elevation [35, 37].
Triggering both reflexes thus confirms the integrity of the cord metamers T12 and L1 and of the afferent and efferent arcs; the presence of the “dartos reflex” also demonstrates the integrity of the autonomic innervation of the scrotum [38].
2.2.4 The Anocutaneous Reflex, Anal Wink, Anal Reflex, Perineal Reflex
Originally described by Rossolimo, the anocutaneous reflex is evidenced by the contraction of the external anal sphincter (EAS) (efferent fibres from S2-S3-S4), stimulated by cutaneous afferents of the pudendal nerve [39]. Its presence, according to authors, inserted in an anticipatory motor pattern with the increase of the intra-abdominal pressure when coughing [40], is indicative for the integrity of the S4 level; easily exhaustible, it is absent in geriatric age and, often, in cord lesions (like other polysynaptic superficial reflexes), of cauda equina and in lesions of the sacral roots.
In suprasegmental lesions of the central nervous system, the reflex did not differ from healthy subjects; however, it could be more pronounced and with a duration of a few seconds [41].
The superficial anal reflex or “anal wink” consists of the contraction of the subcutaneous portion [42, 43] of the EAS in response to stimulation of the skin or mucosa in the perianal area. After a short latency, the contraction first appears homolaterally to stimulation and subsequently contralaterally [44]. The reflex is mediated by the lower haemorrhoidal nerve (S3-S5) and is probably controlled by encephalic centres [45, 46].
The evaluation of the superficial anal reflex is particularly critical for the diagnosis of cauda equina or conus medullaris syndrome: the simultaneous absence and presence of the voluntary contraction of the EAS with the presence of the reflex and tone of the EAS are indicative of a suprasacral lesion.
The superficial anal reflex and the bulbocavernosus reflex are somatic motor reflexes while the internal anal reflex and the scrotal reflexes are autonomic reflexes [47].
The internal anal reflex is elicited when a gloved finger reaches the internal anal sphincter; if the reflex is altered (absence of the reflex contraction of the internal anal sphincter), there is a reduced sphincter tone and a non-immediate closure after defecation [41, 43].
2.2.5 Clitoral-Anal Reflex/Bulbocavernosus Reflex
The bulbocavernosus (or clitoral-anal reflex in the woman) or bulbospongiosus reflex or “Osinski reflex” [48] is a polysynaptic reflex which determines the contraction of the pelvic floor muscles at the compression of the glans or clitoris [49]. Initially described as a reflex capable of invoking the contraction of the bulbocavernosus and ischiocavernosus muscles [50], it was subsequently “modified” giving more emphasis on the contraction of the EAS [51], accessible to the examiner’s view or to the touch.
The compression of the glans penis (or clitoris) is carried out with delicate but firm compressions at intervals of 4–5 s [50, 52–55]; the stimulation uses the afference of the root S2 and the contraction of the bulbocavernosus muscle and the EAS are provided by the S4 and S5 roots.
The reflex is essential for the evaluation of the conus medullaris and the sacral cord metamers; in case of lesion of the cauda equina, it can be absent [56] and generally triggered in case of injury of the superior motor neuron [57].
The conus medullaris and the first lumbar vertebra are usually at the same level: a lesion of the 11th or 12th thoracic vertebra can cause suprasacral lesions of the cord, while a fracture of the first lumbar vertebra may involve sacral metamers.
The simultaneous presence of the superficial anal reflex and the bulbocavernosus (or clitoral-anal) reflex allows hypothesising a normal condition of the second, third and fourth sacral metamers, while its absence a lesion of the second motoneuron or of the corresponding sacral myelomeres; physiologically it may not be present in 20% of women without any neurological disease.
2.2.6 Guarding Reflex
Several authors have studied the increase in pressure which can be measured at the urethral level while coughing or the Valsalva manoeuvre [58, 59]; in addition to the response not equally distributed throughout the urethra (more significant at the distal level), an anticipation of the increase in urethral pressure of about 250 ms compared with the bladder one was also observed. The anticipated reflex activation of the pelvic floor, also demonstrated by ultrasound [60], is controlled by the CNS [61–63]. Clinically it may be triggered by asking the person being examined to cough and observing the “holding” movement of the pelvic floor (more easily detectable in a woman) or, in doubtful cases, by evaluating the palpation of PFM.
There is a response in people with a complete cord lesion above the lumbar level [62], and it is almost always absent in postpartum (although in this last case—as in all situations characterised by stress urinary incontinence [63, 64]—probably myofascial factors, dependant on the thoracolumbar fascia and the transverse muscle of the abdomen, play an essential role).
The reflex may be found in incomplete spinal cord injuries and suprapontine lesions [65].
The lack of “guarding reflex” supraspinal control in suprasacral spinal cord lesions is at the basis of the vesico-sphincter dyssynergia which occurs in this clinical situation [66], and its alteration could be involved in a detrusor overactivity not correlated with clear neurological pictures [67].
2.3 Reflex Alterations and Clinical Pictures
Reflexes are altered in case of pathological situations which compromise the recruitment of the muscles activated by the efferent arc, such as in the case of large scar tissues or the degeneration of muscle fibres observed at the IAS in systemic sclerosis or of the EAS in ALS [68, 69].
In the case of peripheral neuropathies, reflex responses can be precociously compromised, often not corresponding to the recruitment deficit (often minimal), due to the early and prevailing involvement of the afferent component of the reflex itself. In radiculopathies, reflexes can often be normal due to the joint participation of several roots in producing the reflected arc itself; the extensive damage of several roots, however, determines the disappearance of the affected reflexes (cauda equina syndrome) in association with a sensitivity deficit and reduced muscle recruitment.
Superficial reflexes are absent in case of injury of the spinal metamer involved and often absent or normal in case of injury above the metamer itself (epicone syndrome caused by a spinal cord injury to the T11–T12 vertebra). In particular, in case of lesion of the corticospinal tract, it is possible to observe their absence but, in particular as concerns abdominal reflexes, it is essential to correlate the datum to the remaining clinical picture: advanced age, abdominal scars, obesity and multiparity are often associated with their absence.
No significant changes in surface reflexes are observed in cases of cerebellar lesions or those of basal ganglia. In the case of a unilateral encephalic lesion, there is a pattern characterised by the accentuation of proprioceptive reflexes, together with the reduction of superficial reflexes, contralateral to the lesion; bilateral lesions will determine bilaterally similar patterns [70, 71].
