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Arquivos de Neuro-Psiquiatria

Print version ISSN 0004-282XOn-line version ISSN 1678-4227

Arq. Neuro-Psiquiatr. vol.67 no.4 São Paulo Dec. 2009 



Neuropareidolia: diagnostic clues apropos of visual illusions


Neuropareidolia: pista diagnóstica a partir de uma ilusão visual



Péricles Maranhão-FilhoI; Maurice B. VincentII

IMD, PhD, Department of Neurology, Federal University of Rio de Janeiro, Rio de Janeiro RJ, Brazil and Department of Neurosurgery, Brazilian National Cancer Institute, Rio de Janeiro RJ, Brazil
IIMD, PhD, Department of Neurology, Federal University of Rio de Janeiro, Rio de Janeiro RJ, Brazil and Assistant in Neuroscience. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, United States of America




Diagnosis in neuroimaging involves the recognition of specific patterns indicative of particular diseases. Pareidolia, the misperception of vague or obscure stimuli being perceived as something clear and distinct, is somewhat beneficial for the physician in the pursuit of diagnostic strategies. Animals may be pareidolically recognized in neuroimages according to the presence of specific diseases. By associating a given radiological aspect with an animal, doctors improve their diagnostic skills and reinforce mnemonic strategies in radiology practice. The most important pareidolical perceptions of animals in neuroimaging are the hummingbird sign in progressive supranuclear palsy, the panda sign in Wilson's disease, the panda sign in sarcoidosis, the butterfly sign in glioblastomas, the butterfly sign in progressive scoliosis and horizontal gaze palsy, the elephant sign in Alzheimer's disease and the eye-of-the-tiger sign in pantothenate kinase-associated neurodegenerative disease.

Key words: pareidolia, neuroimaging, progressive supranuclear palsy, Wilson's disease, sarcoidosis, glioblastomas, progressive scoliosis and horizontal gaze palsy, Alzheimer's disease, pantothenate kinase-associated neurodegenerative disease.


O diagnóstico em neuroimagem envolve o reconhecimento de padrões específicos indicativos de doenças particulares. Pareidolia, é a perceção equivocada de algo claro e distinto a partir de um estímulo vago e obscuro, por vezes benéfico a quem interpreta exames de imagem na procura do diagnóstico. A este propósito, alguns animais podem pareidolicamente ser reconhecidos em neuroimagens associadas a determinadas doenças específicas, promovendo mais rapidez na habilidade diagnóstica e naturalmente reforçando estratégias mnemônicas individuais na prática do diagnóstico neuroradiológico. Alguns dos sinais de neuroimagens relacionados a percepções pareidolicas de animais são: o sinal do beja-flor na paralisia supra nuclear progressiva; o sinal do panda na doença de Wilson; o sinal do panda na sarcoisdose; o sinal da borboleta no glioblastoma; o sinal da borboleta no escoliose progressiva e paralisia do olhar horizontal; o sinal do elefante na doença de Alzheimeir; e o sinal do olho de tigre na doença degenerativa ligada a pantothenato kinase.

Palavras-chave: pareidolia, neuroimagem, paralisia supranuclear progressiva, doença de Wilson, sarcoidose, glioblastoma, escoliose progressiva e paralisia do olhar horizontal, doença de Alzheimer, doença neurodegenerativa associada a pantothenate kinase.



Pareidolia (from the Greek para - beside; and eidolon - image, form, shape) is a psychological phenomenon characterized by misperceptions of vague stimuli, frequently images and sounds, as meaningful and significant1. Examples include involuntary interpretations of clouds as faces or animals, and perceptions of hidden messages in songs played backwards.

Pareidolia may explain certain visions and holy figures apparitions such as Our Lady silhouette depicted as a shadow on a wall, Saint George riding his horse in the moon, or God's face rendered in the sunlight reflex on a water surface. In Brazil, Saint George is associated with the moon due to influences of African religious traditions. The divinity "Oxossi" is linked to the moon and connected with Saint George. The gray shades seen in the full moon are believed to represent Saint George holding his sword on his horse. Some psychologists even encourage the use of pareidolia to approach patients' psyche using the Rorschach examination2.

Meshberger wrote on his neuroanatomical interpretation of the Michelangelo's oil "Creation of Adam"3. By comparing the image of God wrapped in a swirling cloak surrounded by cherubins depicted at the right side of the picture to a brain sagittal view, he probably provided the pareidolia example with the greatest repercussion in modern medical literature. In a pure pareidolia attempt, convinced that the left-handed master from Florence purposefully included anatomical messages in his pieces, two Brazilian authors wrote a book on putative interpretations of Michelangelo's paintings' details as organs, bones, joints, and a series of other aspects of the human anatomy4.

Macroscopic as well as microscopic aspects of several diseases have been traditionally compared with letters5, inverted letters6, comestibles such as orange7, mango8, rice grain9, onion-bulb10, pear11, tomato12, strawberry jam13, grapes cluster14, honeycomb14, and Swiss cheese15; or objects such as a pencil16, corkscrew17, and candle flame18, or botanic aspects such as leaves19 and bamboo20; or a tooth21.

New and powerful medical imaging techniques have not only significantly expanded our general diagnosis capability, but also inevitably increased pareidolical interpretations of particular visual aspects related to a multitude of nervous system diseases. Recognized as diseases' fingerprints, pictures carrying wildlife resemblance emerge paralleling the imaging technology development. The physician's creativity is the sole limit for medical pareidolia.

We review some of the most interesting illusions characterized by visual resemblance with animals perceived in the neuroimaging field indicative of several central nervous system ailments.



Progressive supranuclear palsy (PSP) is a degenerative disease of the Tau protein pathologies group described in 1964 as "heterogeneous system degeneration" by the neurologist J. Clifford Richardson in collaboration with neuropathologist Jerzy (George) Olszewski and the medical resident John Steele22. PSP is characterized by postural instability with early and frequent falls, axial rigidity-in-extension, supranuclear vertical gaze palsy, as well as pseudobulbar and frontal syndromes. It usually starts at middle age and progresses until decease around six years later, with very poor Levodopa response23.

The brain sagital magnetic resonance (MR) scan may be suggestive of PSP when a pareidolic aspect of either a hummingbird or a king penguin is seen as the result of a mesencephalic tegmentum atrophy with a relatively spared pons (Fig 1).



Reviewing data hitherto available and adding four new cases, Kinnier Wilson wrote his graduation monograph in 1912, a work ever since considered a cornerstone in the literature on the disease named after him24. Wilson's disease is a relatively rare autosomal recessive enzymopathy related with copper metabolism that affects between 1:30,000 and 1:100,000 people25. Symptoms usually start during the second / third decades of life, at first secondary to hepatic copper accumulation. The clinical picture is pleomorphic and includes neurologic, psychiatric, and hepatic signs and symptoms26. In more advanced phases patients may present recurrent hepatitis, cirrhosis, hepatic insufficiency, asterixis, rigidity, tremor, dystonia (with the fixed and rigid wilsonian smile) acatisia; depression, psychosis, phobias, and anti-social behaviour, and the so-called Kayser-Fleischer sign, a copper deposit at the Descement membrane.

The ATP7B gene related to this condition, located to the short arm of chromosome 13, encodes the transmembrane ATPase ATP7B protein that not only plays a role in the copper transport through the Golgi organelle membrane but also helps copper absorption by ceruloplasmine and biliary excretion. More than 300 mutations have been described in the ATP7B gene leading to abnormal copper deposit25.

The diagnosis is based on the clinical picture along with abnormal levels of ceruloplasmine (serum) and copper (serum and urine). The brain MR depicts widespread lesions involving the putamen, globus pallidus, caudate nucleus, thalamus, midbrain, and pons. There may be cortical atrophy and scattered white mater abnormalities as well.

The progressive midbrain involvement leads to the typical pareidolic sign in Wilson's disease: The Mesencephalic Panda Sign27,28 (Fig 2). This sign occurs when the MR signal is preserved at the red nucleus, lateral portion of the substantia nigra pars reticulata; is increased at the mesencephalic tegmentum; and decreased at the superior colliculi.28 Treatment is based on anti-copper agents such as D-penicilamine and Trientine, aimed at quelling copper toxicity. Zinc may be of help as it interferes with copper absorption at the gastro-intestinal tract and therefore reduces its uptake26.



Sarcoidosis is a granulomatous inflammatory multi-systemic disease. Heerfordt, a Danish ophthalmologist, first reported on the neurologic manifestations of sarcoidosis in 190929. The disease affects slightly more females than males, mostly during the third and fourth decades of life, with a prevalence of approximately 10-40:100,00029,30. Although sarcoidosis strictly restricted to the nervous system is unusual, neurologic involvement is relatively common and may represent a diagnostic challenge. The most frequent presentation of neurosarcoidosis is cranial nerve neuropathy, mostly facial and optic. Seizures (15%), chronic meningitis (26%), mental disorders (20%), and intracranial hypertension may also occur29.

The definite diagnosis is based on the clinical picture and histopathological examinations after other afflictions had been excluded. Blood and cerebral fluid tests point to inflammation within the nervous system. Magnetic resonance imaging is required in case of meningitis regardless the presence of sarcomatous parenchymal lesions. Whole-body Galium-67 scintigraphy may show symmetric radiotracer uptake at the lachrymal and parotid glands unveiling the "panda's face" pareidolic aspect (Fig 3). This appearance is not specific and may be found in malignant and inflammatory diseases such as tuberculosis, lymphoma (following irradiation), Sjögren syndrome, and AIDS29 .

Steroids, usually associated with immunosupression, remain as the leading treatment for sarcoidosis.



Glioblastoma (GB), the most malignant central nervous system tumour of the astrocytic cell line, is relatively rare, representing 25% of all malignant tumours, with an annual incidence of 2-3:100,00031. Histopathology shows cellular polymorphisms, nuclear atypia, exuberant mitotic activity, thrombosis with microvascular proliferation, and necrosis, the last two being required provisos for the diagnosis32. Symptoms include motor / cognitive impairment, seizures, and/or headache. Neuroimaging is mandatory. MR spectroscopy may reveal low N-acetyl-aspartate and creatine; high choline and lactate levels. GB appears as hypointense nodules irregularly enhanced by gadolinium in T1-weighed MR images, hyperintense in T2 and FLAIR.

GB tumours that extend from one hemisphere to the other through the corpus callosum may present as an image suggestive of a butterfly ("butterfly wings tumour", Fig 4). Due to its invasive nature, GB can hardly be completely removed, resulting in high post-operative relapsing percentages. One, three, and five years after the diagnosis survival rates remain respectively around 30%, 5% and 3%. Chemo-radiotherapy right after surgery is recommended. Temozolamide has been used as a valid alternative.



Horizontal gaze palsy secondary to progressive scoliosis is a rare autosomal recessive disorder characterized by two main features: (1) Complete or almost complete horizontal gaze palsy with normal convergence and vertical ocular movements; (2) Progressive scoliosis during childhood and adolescence. Asymmetric intermittent blinking and nystagmus may be present33-36. The pathophysiology of this interesting association between distinct neuro-ophthalmological and bone structural abnormalities remained obscure until 2004, when Jen at al. linked the picture to a mutation in the ROBO3 gene located to the long arm of chromosome 11 (11q23-25). The guidance receptor Robo3/Rig1 belongs to a transmembrane receptor family that expresses in growing axons and are indispensable for controlling axons grow, leading them to accomplish their task36. Since ROBO3 protein is required for hindbrain axon midline crossing, its dysfunction causes malformations in brainstem structures as well as non-crossing of corticospinal and posterior spinal tracts. Although the pathophysiology behind progressive scoliosis development remain partially unknown, it has been suggested that the lack of tracts crossing may contribute to bad regulation of the paraspinal muscles tonus and provoke scoliosis36.

The brain MR imaging depicts typical changes, especially in the brainstem. Because the olives are seen more prominent than the pyramids the insinuate aspect of a butterfly37 (Fig 5).



Alzheimer's disease (AD) was described by Alois Alzheimer in 1907 apropos of a 55 year-old patient who presented as first symptom of her ailment extreme jealousy towards her husband. AD is considered today the most frequent dementia38. Initial symptoms typically present as subtle memory deficits, followed by other cognitive impairments39. The definite diagnosis depends on the histopathological finding of extracelullar amyloid plaques and intracellular neurofibrillary tangles originating from abnormal tau protein. Neuronal death progressively leads to atrophy seen on neuroimaging studies.

Medial aspects of the temporal lobes, including the entorhinal cortex and hippocampus are initially affected39, causing the pareidolic aspect of an elephant trunk. - The elephant sign40 (Fig 6). Although hippocampal atrophy has been considered as a biomarker of Alzheimer's disease41. Such findings must be regarded with caution, as other dementias may present medial temporal lobe atrophy. Besides, lack of atrophy does not necessarily rule out Alzheimer's disease42.



Mutations in the genes encoding the pantothenate kinase 2 (PANK2), an enzyme responsible for the biosynthesis of coenzyme A, are associated with a phenotype known as pantothenate kinase-associated neurodegenerative disease (PKAN)43. PKAN typically starts during childhood, presenting progressive gait disturbances, spasticity, hyperreflexia, Babinski sign and cognitive impairment that may evolve to dementia associated with marked extrapyramidal abnormalities such as rigidity, dysarthria, dystonia and chorea43,44. Retinopathy and less frequently optic nerve atrophy may occur. The development is not necessarily constant, sometimes with marked deteriorations lasting two months separated by long periods of relative stability. More than 80% of the patients cannot walk 15 years after the disease onset43.

A correlation exists between the PANK2 gene mutation and the corresponded neuroimaging aspect, showing a hyperintense signal surrounded by a hypointense area at the medial aspects of the globus pailidus, configuring the so-called eye-of-the-tiger sign43 (Fig 7).

Because of ethical reasons, the eponymous term "Hallervorden-Spatz syndrome" has been replaced by the well-accepted denomination "pantothenate kinase-associated neurodegenerative disease" for patients having the PANK2 mutation and "Neurodegeneration with Brain Iron Accumulation (NBIAs)" for those with the phenotype but no demonstrable mutation43,45,46.



Various imaging techniques have developed largely as useful diagnostic tools in modern medicine. Facing a multitude of contrasts and forms, our brains naturally react trying to find familiar patterns matching typical aspects of a certain disorder. This process is similar to finding visual patterns in shadows and clouds, i.e. pareidolia. In terms of neuroimaging, some disorders may present aspects that evoke animals and suggest pareidolic denominations. Such visual illusions help memorization and improve general diagnostic skills.

ACKNOWLEDGEMENT - The authors are in debt with Péricles Maranhão Neto for his technical assistance.



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Received 7 June 2009, received in final form 22 July 2009. Accepted 4 August 2009.



Dr. Péricles Maranhão-Filho - Av. Canal de Marapendi 1680 / 1802 - 22631-050 Rio de Janeiro RJ - Brasil. E-mail:

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