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Show ORIGINAL CONTRIBUTION Environmental Tilt Illusion as the Only Symptom of a Thalamic Astrocytoma AricJ. Aldridge, MD, LanningB. Kline, MD, and Christopher A. Girkin, MD Abstract: A 14- year- old girl experienced two episodes of environmental tilt illusion. During both episodes, which lasted less than 1 minute, she perceived all objects within view as rotated 45 degrees clockwise. There were no auras, accompanying symptoms, or sequelae. Neuro- ophthalmic examination findings were normal except for a right relative afferent pupil defect ( RAPD). Imaging disclosed a cystic mass in the left posterior thalamus with compression of the brachium of the left superior colliculus. Stereotactic biopsy revealed a pilocytic astrocytoma. This is the first case documenting environmental tilt illusion as an isolated symptom of a thalamic lesion. Disruption of vestibular connections between the posterior thalamus and the posterior parietal cortex may be the cause of this visual perceptive disorder. ( JNeuro- Ophthalmol 2003; 23: 145- 147) The illusion of environmental tilt is a disorder of visuo-spatial perception characterized by tilting, flipping, or inversion of the visual environment ( 1,2). This rare phenomenon has been reported to oc cur with pathologic lesions involving the occipitoparietal cortex, the dorsolateral medulla, and, less commonly, the labyrinth or cerebellum ( 1, 3,4). We report a patient who experienced the episodic perception of environmental tilt as the only symptom of a left thalamic astrocytoma. Her only neuro- ophthalmic abnormality was a right RAPD, presumably owing to compression of the left brachium of the superior colliculus ( 5- 9). We believe that this is the first case documenting environmental tilt illusion as an isolated symptom of a lesion in this location. CASE REPORT A 14- year- old girl reported two 30- second episodes of perceived environmental tilt. The first occurred at school Department of Ophthalmology, University of Alabama School of Medicine, Birmingham, Alabama. Address correspondence to Lanning B. Kline, MD, Suite 601, 700 South 18th Street, Birmingham, AL, 35233, USA; E- mail: LKline@ UABMC. edu Presented in part at the Annual Meeting of the Frank B. Walsh Society, Copper Mountain, Colorado, February 10, 2002. Supported in part by an unrestricted grant from Research to Prevent Blindness, New York, New York. as she approached the dining table and placed her lunch box on it. She experienced a 45- degree clockwise rotation of the table such that her lunch box appeared to lie on the floor. The entire room was noted to tilt during the episode. As she sat at the table, the rotation gradually resolved over a 30- second period. Several friends were with her during the event and none reported observing signs of seizure activity, loss of consciousness, or inappropriate behavior. In fact, the patient was entirely aware of what was happening for the duration of the episode. Approximately 5 months later, a second episode occurred in similar fashion at home with perceived rotation of the television set and room. The television set and the objects around it rotated 45 degrees clockwise. During this episode, she " followed" the perceived rotation by leaning to her right until it began to reverse at a point when she was lying on her right side. The entire episode lasted approximately 30 seconds. Her father witnessed the event and noted no associated signs. As with the first episode, she was fully aware of the phenomenon and there were no auras, loss of consciousness, headache, seizure activity, vertigo, or other neurologic signs or symptoms. Her medical and family histories were negative. Her only medication was loratadine ( Claritin, Schering [ U. S.]). She denied use of any psychotropic substances. General medical and neurologic examinations were unremarkable. Magnetic resonance imaging of the brain demonstrated a cystic mass in the left posterior thalamus with compression of the brachium of the left superior colliculus ( Fig. 1). Stereotactic biopsy of the lesion revealed a benign pilocytic astrocytoma ( Fig. 2). The patient was referred for neuro- ophthalmic consultation. Best- corrected visual acuity was 20/ 20 OU. Pupils measured 4 mm OU, briskly reactive to light with a right RAPD. Color vision was normal by Ishihara pseudo-isochromatic plate testing, and visual fields were full by manual and automated ( SITA- Standard) methods. Eye movements were intact, and anterior and posterior segment examination findings were within normal limits OU. Management options offered to the patient and her parents included stereotactic radiosurgery or observation with serial MRI scanning. The family chose to observe with serial scans. Imaging studies and clinical examinations have remained stable over 20 months of follow- up. Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. J Neuro- Ophthalmol, Vol. 23, No. 2, 2003 145 JNeuro- Ophthalmol, Vol. 23, No. 2, 2003 Aldridge et al. FIG. 1. A: Fluid- attenuated inversion recovery axial magnetic resonance imaging ( MRI) scan demonstrates a mass lesion { arrow) in the left posterior thalamus in the region of the brachium of the superior colliculus, explaining the relative afferent pupil defect. B: Unenhanced T1- weighted sagittal MRI reveals the mass to have a cystic component { arrow). DISCUSSION Environmental tilt illusion, also known as tilt of the subjective visual vertical, is a disorder of visuospatial perception ( 1- 4). This rare phenomenon has been reported to occur in association with pathologic lesions in seemingly disparate areas of the brain, such as the occipitoparietal cortex, medulla ( in dorsolateral medullary stroke of Wallenberg), otolithic pathways in the peripheral vestibular organ, labyrinth, cerebellum, and thalamus. Potential causes include tumor, infection, infarction, trauma, multiple sclerosis, seizure, and migraine ( 1,10- 14). The cause of the environmental tilt illusion is unknown. Tiliket et al ( 3) have suggested that it may result from a disorder of integration of visuospatial input. This disorder could arise from a lesion at the level of the brain stem, with abnormal integration of visual and otolithic inputs, or at the cerebral cortex, where there might be an inability to integrate visual and somesthetic information. The posterior parietal cortex has been shown to contain an abstract representation of space constructed from integration of inputs from several sensory modalities ( 15- 17). Pathologic lesions disrupting this area of higher order visuospatial processing can result in the phenomenon of visual environmental rotation ( 1). In our patient, the lesion was confined to the posterior thalamus, a complex relay center interposed between sensory and motor loci within the brain. It is subdivided into six FIG. 2. Biopsy of thalamus shows features consistent with pilocytic astrocytoma. A: Hypercellular neoplastic tissue on the left contrasted with normal tissue on the right ( hematoxylin and eosin, magnification X200). B: Neoplasm reveals small, pleomorphic hyperchromatic nuclei, disorganized architecture, and Rosenthal fibers { arrow) ( hematoxylin and eosin, magnification X400). Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. 146 © 2003 Lippincott Williams & Wilkins ENVIRONMENTAL TILT ILLUSION JNeuro- Ophthalmol, Vol. 23, No. 2, 2003 groups of nuclei, one of which is the largest and most posterior of the thalamic nuclei, the pulvinar, where our patient's lesion was centered. The pulvinar receives afferent inputs from the superior colliculus, as well as the temporal, parietal, and occipital lobes, and sends efferent information to these three cerebral hemispheric lobes ( 18). Mapping studies in the macaque monkey have shown that the inferior and lateral posterior- pulvinar subnuclei contain a complete visuotopic representation of the contralateral visual field. The inferior pulvinar receives inputs from the superior colliculus as well as corticothalamic projections from the primary visual cortex. It sends projections to extrastriate and inferotemporal areas. The lateral posterior- pulvinar complex also receives corticothalamic inputs from cortical areas containing visuotopic maps, including the primary visual cortex. It sends efferent projections primarily to the posterior parietal cortex ( 19). Additional mapping studies in the rhesus and macaque species have localized the vestibular thalamic nuclei to the posterolateral thalamus near the pulvinar. The specific subnuclei in the human believed to correlate most closely with those of these animals include the Vim ( nucleus ventro- oralis intermedius), Vce ( nucleus ventro-caudalis externus), Dc ( nucleus dorsocaudalis), and Vci ( nucleus ventrocaudalis internus) ( 2,20). Thalamic infarctions in this region have been shown to cause environmental tilt illusion in the absence of the other components of the ocular tilt reaction ( 20). The interaction of vestibular input with inputs from other sensory modalities has been demonstrated from the level of the vestibular nuclei in the brain stem to the thalamus and cortex. Mapping studies in the rhesus monkey have demonstrated vestibular input to a parietal area that may correspond to the vestibular area located within the human intraparietal sulcus of the posterior parietal cortex. Moreover, neurons in this region are known to be sensitive indicators of visual- field motion, demonstrating the role of vestibular input in spatial orientation ( 21). We suggest that disruption of vestibular connections between the posterior thalamus and the posterior parietal cortex is the cause of our patient's visual perceptive disorder. To our knowledge, this is the first case documenting visual tilt illusion in the absence of other neurologic findings ( except for a RAPD) in the setting of an isolated lesion of the posterior thalamus. Other investigators have reported this illusory phenomenon in thalamic disorders, but the patients have had other neurologic findings such as hemiparesis, hemisensory loss, or hemiataxia ( 20). More commonly, this illusion has arisen in the setting of lesions in the brain stem or cerebral cortex, areas previously incriminated as causing this phenomenon ( 22). REFERENCES 1. Girkin CA, Perry JD, Miller NR. Visual environmental rotation: a novel disorder of visiospatial integration. JNeuroophthalmol 1999: 19: 13- 6. 2. Brandt T, Dieterich M. Vestibular syndromes in the roll plane: topographic diagnosis from the brainstem to cortex. Ann Neurol 1994: 36: 337- 47. 3. Tiliket C, Ventre- Dominey J, Vighetto A, et al. Room tilt illusion: a central otolith dysfunction. Arch Neurol 1996; 53: 1259- 64. 4. Ropper AH. Illusion of tilting of the visual environment: report of five cases. J Clin Neuroophthalmol 1983; 3: 147- 51. 5. Eliott D, Cunningham ET Jr, Miller NR. 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