Expanded A NEW DIMENSION IN COMPLEX SOFTNESS

SUMMARY: Visual hallucinations are relatively uncommon presentations in medical and psychiatric clinics, where they are generally regarded as a marker of possible underlying “organic” brain disease. Thus, patients with visual hallucinations are often referred for imaging of the brain. This article presents a pragmatic approach for the radiologist reviewing such imaging. Because conditions that can present with visual hallucinations are legion, a familiarity with the features of the hallucinations themselves, which can serve as clues to the underlying cause, can be helpful in interpreting such cases. We consider the nature of visual hallucinations and themechanisms underlying their formation. We then provide a framework to guide the search for their cause, first in terms of focal lesions along the visual pathway and then global conditions affecting 1 region. ABBREVIATIONS: CJD Creutzfeldt-Jakob disease; VH visual hallucination The presentation of visual hallucinations (VHs) to general medical and psychiatric clinics often triggers a search for underlying “organic” brain disease and a referral for imaging of the brain, first with CT and then MR imaging. If the findings are interpreted as normal, patients who in actuality have underlying organic disease can have delays in diagnosis and prolonged inappropriate management. Therefore, it behooves the reporting radiologist to be familiar with visual hallucinations and the possible causes thereof. The organic causes of VHs represent a veritable Augean stable of pathologies, ranging widely in etiology and location within the brain (Table 1). Although in some instances, a focal defined lesion can lead to VHs (eg, an occipital lobe cavernoma), pathology can also affect large or multiple areas simultaneously (eg, posterior cortical atrophy or Creutzfeldt-Jakob disease [CJD]). When one reviews scans of patients with VHs, it is important to assess not only each part of the visual system but also more diffuse, global, or multiregional pathologies. We have pragmatically divided this article into focal and global causes based simply on localization rather than on a clear understanding of the pathophysiology of VHs. We briefly consider the nature of hallucinations and clues in the clinical context on the request form. We then consider mechanisms underlying the formation of VHs to guide the search for their cause. We suggest looking first at focal lesions along the visual pathway and then conditions affecting 1 region. Only when no lesion is found and in the absence of other organic clinical features should functional causes then be considered. Types of Visual Hallucinations A hallucination is a “percept without object,” “a sensory perception that has the compelling sense of reality but that occurs without stimulation of the relevant sensory organ.” Hallucinations are distinguished from the following: 1) distortions, in which the real objects are perceived as changed in some way; 2) illusions, in which the perception of real objects is transformed in size (micropsia or macropsia), shape (metamorphopsia), or color (dyschromasia) or into other objects; or 3) pseudohallucinations, which arise from vivid inner mental experience and can often be recognized as such. Although hallucinations are experienced as real, patients experiencing them have varying degrees of insight into the nature of their experiences, which engender varying responses, from indifference to marked distress. Hallucinations vary in content and complexity and occur in every sensory technique: Visual hallucinations are commonly linked to underlying organic etiology but also occur frequently in psychotic states, though half as commonly as auditory hallucinations. Olfactory, tactile, and gustatory hallucinations occur From the Departments of Neuropsychiatry (T.T.W.-B., R.M., D.V.) and Radiology (A.T., F.G.), Royal Melbourne Hospital, Parkville, Victoria, Australia; and Melbourne Neuropsychiatry Centre (D.V.), National Neuroscience Facility, Carlton, Victoria, Australia. Please address correspondence to Frank Gaillard, Royal Melbourne Hospital, Grattan St, Parkville, 3050 Victoria, Australia; e-mail: [email protected] Indicates open access to non-subscribers at www.ajnr.org Indicates article with supplemental on-line table. Indicates article with supplemental on-line photo. http://dx.doi.org/10.3174/ajnr.A4636 774 Winton-Brown May 2016 www.ajnr.org less often and are seen in a variety of both psychiatric and organic conditions. The use of the term “organic” here is by convention and should not be taken to imply an absence of brain dysfunction in psychiatric illness. The content of visual hallucinations can offer some clue as to their origin (Table 1) and may relate to the mechanism of production. Simple Visual Hallucinations. Brief, stereotyped unformed flashes of light and color or indistinct forms may reflect stimulation or irritation of primary visual areas, for example by tumor, migraine, or focal epileptogenic lesions. Complex Visual Hallucinations. In contrast, complex visual hallucinations suggest disruption to the wider visual system and include branching or tessellated patterns, individuals or crowds of people, animals, and complex scenes often associated with sensory distortions. Lilliputian hallucinations, classically seen in alcohol withdrawal and delirium, are complex VHs consisting of miniature people in lines or groups performing strange actions and eliciting curiosity or wonder. Complex VHs due to psychiatric disturbance, delirium, or intoxication/withdrawal are often perceived as real and frightening, while those seen in peduncular hallucinosis or the Charles Bonnet syndrome may provoke indifference, and insight into the nature of the experience as unreal may be preserved. Associated symptoms such as headaches or focal seizures may help point toward a specific etiology, as may the presence of associated deteriorating cognitive function, focal neurologic symptoms, or psychiatric symptoms (Table 2). Visual Pathway and Mechanisms of Disruption The anatomy of the primary visual pathway is well-described: Information from the retina passes along the optic nerve, chiasm, and tract to the lateral genicuFIG 1. Visual pathways. A, Retino-geniculo-calcarine tract. Optical information from the retina (1) passes along the optic nerve (2) through the optic chiasm (3) and optic tract (4) into the lateral geniculate nucleus of the thalamus (5), where it receives input from the superior colliculus (7) via the pulvinar (6) and then traverses the optic radiation (8 and 9) through the temporal lobe (13) into the visual cortex (10–12). B, Intersection of ascending pathways. Optical information in the retino-geniculo-calcarine tract (1–8 and 11) is modulated by ascending input from the pedunculopontine and parabrachial nuclei (9) and raphe nuclei (10) via the superior colliculus (7).Hashed areas show regions where interruptions are known to produce visual hallucinations: in the retino-geniculo-calcarine tract via deafferentation, in the thalamus through reducing signal-to-noise ratio, and in the ascending pathways via removal of inhibitory control. Reproduced with permission from Dr. Ramon Mocellin. Table 1: Type of hallucination Feature Possible Cause Monocular Eye disease or optic nerve proximal to optic chiasm Limited visual field Focal lesion in visual pathway Simple, brief, unformed Eye disease, migraine, seizure, calcarine lesions Visual distortion Seizures, CJD Lilliputian Delirium, intoxication, withdrawal Frightening Delirium, hallucinogens, psychosis Unconcerned/preserved insight Charles Bonnet syndrome, peduncular hallucinosis Table 2: Associated symptoms Feature Possible Cause Vision loss Charles Bonnet syndrome Headache, nausea/vomiting Migraine Impaired/fluctuating level of consciousness Delirium, epilepsy Confusion/disorientation Delirium, intoxication, encephalopathy, dementia Focal neurologic signs Space-occupying lesion Agitation, depression, mania, anxiety, disordered/unusual thought content Delirium, intoxication, psychiatric disorders (psychosis, severe mood disorders) AJNR Am J Neuroradiol 37:774–81 May 2016 www.ajnr.org 775 late nucleus in the thalamus and then to the optic radiation through the temporal lobe to the primary and secondary visual cortices (Fig 1). The flow of visual information is modulated by ascending input from the pedunculopontine and parabrachial nuclei and raphe nuclei via the superior colliculi (Fig 2) and involves the cholinergic, GABAergic, and glutamateric systems (Fig 2). Interruptions to this system at any point, either in the primary direct pathway or in its ascending modulatory projections, may lead to visual hallucinations. One series by Braun et al suggested that the occipital and occipitotemporal regions were the most commonly implicated cortical regions, and the midbrain, cerebral peduncles, pons, and thalamus, the usual subcortical regions. A search for focal lesions on MR imaging should progress with this