An Evaluation of the Role of fMRI in Patients with Lower Urinary Tract Dysfunction

Review Article

Austin J Urol. 2019; 6(1): 1062.

An Evaluation of the Role of fMRI in Patients with Lower Urinary Tract Dysfunction

Ghanem MA1,2*, Adawi EA1, Hendi AH3 and Ghanem AA4

¹Department of Urology, Jazan University, KSA

²Department of Urology, Menoufiya University, Egypt

³Radiology Department, Jazan University, KSA

4Gynecology and Obstetric Department, Mansoura University, Egypt

*Corresponding author: Ghanem MA, Department of Urology, Jazan University and Menoufiya University, KSA and Egypt

Received: September 09, 2018; Accepted: February 15, 2019; Published: February 22, 2019


Lower urinary tract dysfunction, including urinary incontinence and Overactive Bladder (OAB) syndrome, have detrimental effects on health-related quality of the life and also exert a significant economic burden on health care systems. The role of imaging in managing urinary incontinence is diagnostic and reserved only for situations based on clinical and/or neurophysiological test findings.

Recently, the field of fMRI has grown explosively and is fast becoming a regular feature in the news media. fMRI emerges a useful research tool for voiding dysfunction studies. With this modern brain imaging, it is now possible to identify the role of the supraspinal control system and brain areas in the living human brain involved in voluntary control of the micturition reflex.

So, the combination of anatomical and functional information by fMRI enabled us in the diagnosis of a wide range of diseases which may cause urinary dysfunction and to develop individual accepted recommendations for all patients. So, it assisted in the decision-making processes between invasive and conservative management for voiding dysfunction patients.

Keywords: Urinary dysfunction- OAB; Urinary urgency- fMRI


Patients with Lower Urinary Tract Symptoms (LUTS), including urinary incontinence and Overactive Bladder Syndrome (OAB) constitute a considerable part of urology patients. The prevalence of storage LUTS (men, 51%; women, 59%) was greater than that for voiding (men, 26%; women, 20%). The prevalence of OAB was 12% which was more prevalent than all types of urinary incontinence combined (9%) [1]. Also, OAB affects approximately 15% of urgency women and prevalence rates are higher in women than men [2].

The cause of the urinary dysfunction is usually multifactorial. Although urinary dysfunction may entirely be non-neurogenic, it may also present with an overt or occult neurogenic abnormality underneath [3]. Many clinically relevant methods have been put forward to allow an early diagnosis and identification of urinary dysfunction. A detailed patient's history, physical examination, and the determination of underlying pathophysiology are considered essential components of the initial evaluation of urinary dysfunction [4].

Beyond these assessments, there are no universally accepted imaging recommendations for urinary dysfunction and, to date, imaging is indicated only if pelvic pathology is suspected; Videourodynamics (VUDE) and cystourethrography are considered optional diagnostic tests and continue to be refined; fMRI is considered an important research tool in evaluating lower urinary tract disorders, but at present its clinical role remains investigational [5].

Neurophysiology and Pathophysiology of Micturition: Normal Volunteers

Peripheral and central processes control Micturition, in the conscious and unconsciousness states. Peripheral innervations arise from caudal segments of the sacral spinal cord, passes through the cauda equina to the sacral plexus, and via pelvic and pudendal nerves to the bladder and sphincter. The parasympathetic nervous system controls bladder contraction and micturition, and the sympathetic system becomes especially active during the last part of urine storage when micturition is actively postponed [6,7].

It is generally accepted that the brain plays an important role in normal micturition [8]. Depending upon the stage of storage and voiding process, a network involving subcortical and cortical structures was identified. A part of the pons and the Periaqueductal Gray (PAG) showed activity as the bladder filled and during emptying. Further activation was observed in some regions of the cerebral cortex, i.e. frontal lobe, insula and anterior cingulated gyrus, as well as in the cerebellum, putamen, thalamus, and hypothalamus. The activation of the insular cortex is triggered by sympathetic stimulation of the urethral sphincter [9,10].

Furthermore, the PAG plays a crucial role in regulating the micturition reflex. The PAG directly receives information about the bladder filling and if they exceed a certain threshold, the reflex is triggered and a signal is sent to an area in the dorsomedial pontine tegmentum, referred to as the Pontine Micturition Center (PMC) called Barrington’s area or M–region. PMC excitation will produce complete synergic micturition via long descending motor efferents pathways to the parasympathetic bladder motor neurons and to sacral GABA-ergic (gamma amino butyric acid) and glycinergic premotor interneurons that inhibit motorneurons in Onuf’s nucleus which would lead to sphincter and pelvic diaphragm relaxation. In addition, the excitatory parasympathetic pathway leads to detrusor contraction [9,11]. PAG is also known as an area responsible for emotional response, which explain the urge to void during anxiety and emotional stress [5,12]. However, the circuitry controlling micturition from the higher regions of the brain remained unclear.

Since the introduction of fMRI as an imaging modality, there has been a growing interest in its use as an investigative tool in the evaluation of patients with voiding dysfunction. Despite the increasing number of animal and human experimental fMRI studies, its application concerning central micturition control network and the voiding control mechanism in suprapontine structures is rare. To our knowledge little information has been reported on followup fMRI in these patients and to what extent this new modality may affect its management.

Basic role of fMRI in brain scanning

FMRI methods are used as a powerful tool for the noninvasive mapping of brain’s functional localization and connectivity. In functional brain MRI, the term may refer to congnitive function, while the actual brain function occurs in neuronal activity; fMRI is adept in characterizing the associated haemodynamic responses.

Based on Blood Oxygen Level Dependent (BOLD) contrast, fMRI takes advantage of the changes in signal intensity, which arise due to alterations in the local transverse relaxation times, associated with regional changes in cerebral deoxyhemoglobin concentration. FMRI quantifies paramagnetic properties of oxygenated and deoxygenated hemoglobin, which correlate with neuronal activity related changes in blood flow [13].

In noninvasive neuroimaging, neural activity is inferred from fluctuations in deoxyhemoglobin. FMRI BOLD signal demonstrated that there is a strong coupling between local field potentials and changes in tissue oxygen concentrations in the absence of spikes. These results imply that the BOLD signal is more closely coupled to the synaptic activity. So, neurometabolic coupling in cerebral cortex reflects synaptic more than spiking activity. Due to the small signal activity change which results, the correlation between the task activity and fMRI response identified in a statistical manner, using series of images acquired during alternating periods of activity triggered paradigm experiment or any trigger e.g. by pelvic floor muscle contraction in alternation with periods of rest. After this holding for a suitable level of statistical significance, the T-map of the correlation is displayed as a color-coded image in which the color is indirectly related to neuronal activation [14].

Furthermore, resting-state fMRI can elucidate and monitor multiple brain activity regions during voiding in normal persons and correlate with one another at rest. By using this method, better understanding of normal voiding under normal physiological conditions as well as changes that may occur in voiding dysfunction were studied [15]. Furthermore, Diffusion Tensor Imaging (DTI) enables visualization of brain tissue microstructure, which is extremely helpful in understanding various neuropathologies and neurodegenerative disorders. In DTI, the white matter tracts are analyzed by inference from the local diffusion of water molecules. So, the DTI method helps to identify the deficits in white matter that appear normal by conventional radiological imaging methods. Deficits of this region are more prevalent in younger patients and might lead to urgency [16].

Arterial Spin Labeling (ASL) is another type of fMRI technique that allows quantitative measurement of absolute cerebral perfusion [17]. Unlike PET scans that require the administration of radioactive intravenous contrast to measure cerebral perfusion, ASL uses inverted proton spins of magnetically labeled water in the blood as a tracer. ASL fMRI can non-invasively quantify perfusion changes in the brain using a non-catheterized oral fluid challenge paradigm that does not require repeated filling and emptying the bladder, unlike BOLD fMRI [17,18]. The advantage of an oral fill protocol is that it prevents false positive afferent signals induced by placement of a catheter, especially in conditions such as OAB that are characterized by increased afferent signaling. The disadvantage of this protocol is that it does not allow bladder filling volumes to be precisely controlled. The type of fill protocol used during imaging studies depend on the goals of the project [18].

Role of fMRI in studying brain- bladder control of micturition

Recent function imaging studies fMRI reveals a network of brain regions that responds to different signals provoked by bladder filling in response to water intake or furosemide. In the early stages of fMRI studies, urodynamic recordings were not possible in the magnetic field of the scanner. However, a recent study has adapted urodynamic methods to the fMRI environment, so as to monitor bladder pressure and brain activity in the scanner simultaneously during bladder filling [13].

Functional studies have shown that control of bladder is a complex process. The process of the central control mechanisms of bladder function involves spinal reflexes and interactions between the higher brain centers as well as many other brain regions [19]. The role of spurapontine brain structures in the voluntary control of voiding by fMRI based on the pelvic floor muscle function. The idea is that repeated pelvic floor muscle contractions during full bladder induce a stronger contrast of bladder sensation, desire to void, and the effect of this contraction was thought to be activation of the continence areas, and inhibition of the micturition reflex triggering, when the subjects were asked not to urinate. Activation maps calculated by contrast of subtracting the two different conditions were applied to reveal these brain areas that are involved during the inhibition of the micturition reflex [20].

Response differs in subjects with good or with poor bladder control. Among those with poor control, cortical responses were exaggerated at larger bladder volumes and are consistent with symptoms of urgency and frequency. These abnormalities are associated with adequate response to bladder filling in a specific bilateral region of the orbitofrontal cortex, an area known from clinical lesion studies to be crucial to voluntary bladder control. Among subjects with good control, this strengthening of response was prominent in the orbitofrontal cortex. This suggests a similar neurophysiological basis in dysfunction of the orbitofrontal cortex for poor bladder control in absence of neurological lesion [13].

FMRI detected activation of many brain regions involved in bladder control, including PAG, thalamus, insula, cingulate gyrus, ventromedial cerebellum, PMC and preoptic hypothalamus (Figure 1).

Citation: Ghanem MA, Adawi EA, Hendi AH and Ghanem AA. An Evaluation of the Role of fMRI in Patients with Lower Urinary Tract Dysfunction. Austin J Urol. 2019; 6(1): 1062.ISSN:2472-3606