power of the metaphor: forty signs on brain imaging

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Power of the Metaphor: Forty Signs on Brain Imaging

Rahsan Gocmen, MD, Ezgi Guler, MD, Ilgaz Cagatay Kose, MD, Kader K. Oguz, MDFrom the Department of Radiology, Hacettepe University Faculty of Medicine, Sihhiye, Ankara 06100, Turkey

Keywords: Brain, signs, magnetic reso-nance imaging, computed tomography.

Acceptance: Received October 25,2013. Accepted for publication Novem-ber 23, 2013.

Correspondence: Address correspon-dence to Rahsan Gocmen, Departmentof Radiology, Hacettepe University Fac-ulty of Medicine, Sihhiye, Ankara 06100,Turkey. E-mail: [email protected]

J Neuroimaging 2014;00:1-17.DOI: 10.1111/jon.12086

A B S T R A C TWe retrospectively reviewed neuroradiology database at our tertiary-care hospital tosearch for patients with metaphoric or descriptive signs on brain computed tomographyor magnetic resonance imaging. Only patients who had clinical or pathological definitivediagnosis were included in this review.

IntroductionThe history of the medicine is replete with metaphorical de-scriptions. Metaphors play an important role in medicine, par-ticularly illustrative branches such as radiology, dermatology,microbiology, and pathology. Neuroradiology literature alsoencompasses a variety of interesting metaphoric and descriptivesigns. We illustrate the characteristic 40 metaphoric or descrip-tive signs of a broad spectrum of conditions in neuroradiology.

We retrospectively reviewed neuroradiology database from2006 to 2013 at our tertiary-care hospital to search for patientswith metaphoric/descriptive signs on brain computed tomogra-phy (CT) or magnetic resonance (MR) imaging. Only patientswho had clinical or pathological definitive diagnosis were in-cluded in this review.

FindingsA. Congenital Malformations

1. “Tectal beaking” sign: Chiari II malformation

“Tectal beaking” refers to the triangular (beaked) appear-ance of the tectum on the sagittal views in Chiari type-II(Arnold-Chiari) malformation.1 The midbrain is elongated cau-dally and posteriorly to overlie the midline cerebellum and thepons (Fig 1). Variable degrees of fusion of the colliculi andtectum result in a beaked tectum.

2. “Steer-horn” ventricles: Agenesis of the corpus callosum

The “steer-horn” sign refers to the abnormal shape of thefrontal horns of the lateral ventricles on coronal MR im-

ages in patients with corpus callosum (CC) agenesis (Fig 2).The lack of supporting deep white matter fibers and associ-ated the redirection of longitudinal callosal fibers (Probst bun-dles, arrows), result in bulging of the roof of the third ven-tricle into the interhemispheric fissure, widely separated andmedially concaved frontal horns, with the frontal horns tak-ing on a “steer or bull’s horn” appearance in the coronalview.2

3. “Bat-wing” sign: Joubert syndrome

Joubert syndrome is an autosomal recessive disorder wherethere is agenesis of the cerebellar vermis to varying degrees.There is an absence of decussation of the superior cerebellarpeduncles (SCP) and pyramidal tracts. The absence of the ver-mis is responsible for a dilated, distorted, and rostrally deviatedfourth ventricle; and it causes an appearance of a “bat-wing” oran umbrella3 (Fig 3A and B).

4. “Molar tooth” sign: Joubert syndrome

The deeper and wider interpeduncular cistern (Fig 4A; ar-row) and thicker, elongated, and horizontal SCP (Fig 4B; ar-rows) give the shape of a “molar tooth” on MR axial images;this is one of the most consistent imaging finding in Joubertsyndrome.4 Also note that a lack of “central red dot” sign(Fig 4C) corresponding to the decussating fibers of the SCPon axial colored-fractional anisotropy (FA) map image. TheFA map in a normal individual shows “central red dot” sign(Fig 4D).

Copyright ◦C 2014 by the American Society of Neuroimaging 1

Fig 1.

5. “Tram-track” sign: Sturge-Weber syndrome

“The tram-track” sign is caused by cortical calcificationsin Sturge-Weber syndrome.5 This sign can be observed onplain radiograph, noncontrast CT (NCCT) scans (Fig 5A). OnNCCT, “tram-track” calcification is usually seen before 2 yearsof age. The metaphor of the tram-track which is one of themost favorite radiologic descriptions also has been described inoptic nerve meningioma. The tram-track sign is most evidenton contrast–enhanced CT or fat-suppressed T1-weighted MRimages of the orbit. On these images, the optic nerve appears

Fig 2.

as an unenhanced central linear structure (negative defect) inrelation to the surrounding enhancement in the area of theoptic nerve sheath on either side (Fig 5B). It is helpful indistinguishing dural diseases from optic nerve glioma.

6. “Pancake” sign: Holoprosencephaly

The “pancake” sign refers to the appearance of the cere-bral parenchyma in patients with a lobar holoprosencephaly(AH).6 AH, is characterized by a mono-ventricle, small, con-tiguous brain tissue that may have a cup, ball, or a pancake

Fig 3.

2 Journal of Neuroimaging Vol 00 No 0 xxxx 2014

Fig 4.

Fig 5.

Gocmen et al: Neuroradiology Signs 3

Fig 6.

Fig 7.

configuration, fusion of the thalami, and absence of the in-terhemispheric fissure, cavum septum pellucidum, CC, optictracts, and olfactory bulbi (Fig 6).

7. “Corduroy” sign: Lhermitte-Duclos syndrome (aka dysplasticgangliocytoma)

Fig 8.

The “corduroy” appearance refers to thick cerebellar foliarpattern that consists of alternating bands on T1- and T2W imag-ing in Lhermitte-Duclos disease (LDD).7 The maintenance ofthe overall cerebellar architecture in spite of the thickened, andhyperplastic folia is responsible for this characteristic imagingappearance (Fig 7). LDD (also known as dysplastic gangliocy-toma) is a rare probably hamartomatous disorder involving thecerebellum. The debate on whether it represents a neoplasm,malformation, or hamartoma, still continues.

8. “Figure-eight” : Lissencephaly

“Figure of 8,” also known as “hourglass configuration” refersto the appearance of the brain in the type I lissencephaly.8

Type I lissencephaly is a migration disorder of the gray matter,with the formation of a smooth, thick but four-layered cortex.Sylvian fissures are shallow, verticalized, and the brain takes a“figure-eight” configuration because of a narrowing at its middleportion by the Sylvian fissures (Fig 8).

9. “Key-hole” sign: Dandy–Walker syndrome

The key-hole appearance is caused by communication be-tween cisterna magna and dilated 4th ventricle9 (Fig 9A andB). The Dandy–Walker malformation complex refers to agroup of congenital central nervous system (CNS) malforma-tions that primarily involves the cerebellum and surroundingstructures. The diagnostic nomenclature in this field is con-fusing, in part because this complex may be regarded as aspectrum of posterior fossa abnormalities, which includes di-latation of the fourth ventricle, varying degrees of cerebellarvermis hypoplasia or aplasia, and elevation of the transverse si-nuses and torcular herophili. The key-hole shaped 4th ventriclehas also been described in rhombencephalosynapsis (Fig 9C).


Fig 9.

Fig 10.

Fig 11.


Fig 12.

Fig 13.

Fig 14.


Fig 15.

Fig 16.

B. Vascular/Stroke

10. Dense middle cerebral artery (MCA): Acute thrombosis

The dense MCA sign is one of the early signs of infarct(Fig 10A–D). This is due an increase in density of its prox-imal segments, secondary to thrombosis.10 The correspond-ing sign on susceptibility-weighted imaging (SWI) has beencalled as “MCA-susceptibility-sign.” False-positive results may

Fig 17.

Fig 18.

occur, in cases with vascular calcification, focal subarach-noid hemorrhage in the Sylvian fissure, and high haemat-ocrit. The dense artery sign can also be seen in basilar arterythrombosis.

11. “Cord” sign: Cortical venous thrombosis

The “cord” sign is characterized as increased density ofthe cortical or deep veins on NCCT, originated from the


Fig 19.

thrombosed material inside the affected vessel.11 Diagnosis ofthe venous infarct is elusive because of the wide variety of clin-ical and radiologic manifestations, mimicking arterial infarct orother diseases. “Cord” sign is a rare, but an invaluable clue fordiagnosis of the venous thrombus (Fig 11A and B).

12. “Spot” sign: Active bleeding within hematoma

The “spot” sign refers to tiny enhancing foci on CT angiog-raphy (CTA) source images and refers to active bleeding.12 It’sbeen regarded as a predictor of hematoma expansion. NCCTscan demonstrates spontaneous intracerebral hematomain theright thalamus (Fig 12A). Axial maximum intensity projectionview of CTA reveals that small foci of enhancement consis-tent with the “spot sign” (Fig 12B, arrow). Marked hematomaexpansion is demonstrated on follow-up CT scans (Fig 12C).

Fig 20.

13. Insular “ribbon” sign: Acute MCA infarct

This refers to hypodensity and swelling of the insularcortex13 (Fig 13A, arrow). It is a very indicative and subtleearly CT-sign of infarct in the territory of the ipsilateral MCA.Figure demonstrates normal insular ribbon appearance on theright cerebral hemisphere (Fig 13B).

14. “Reversal” sign or white cerebellum: Diffuse cerebral hy-poxic/anoxic injury

The “reversal sign” represents severe anoxic-ischemic braininjury resulting in irreversible brain damage and carries apoor prognosis. CT features of the “reversal” sign are diffuselydecreased density of cerebral cortical gray and white matterwith a decreased or lost gray/white matter interface, or reversal

Fig 21.


Fig 22.

of the gray/white matter densities and relatively increaseddensity of the thalami, brainstem, and cerebellum14 (Fig 14Aand B).

15. “Popcorn” sign: Cavernous malformation

The cavernous malformation, also known as cavernous he-mangioma or cavernoma, is an abnormal vascular lesion. It hastypically “popcorn” appearance T1 bright locules of methe-moglobin with a low signal intensity hemosiderin rim on T2Wimages15 (Fig 15). Perilesional edema or mass effect is unusual

Fig 23.

unless there is an associated hemorrhage or multiloculated cav-ernoma. Blooming on gradient echo images are due to param-agnetic effect of blood degradation products.

16. “Zebra” sign: Remote cerebellar hemorrhage

This sign refers to typical, streaky bleeding pattern dueto blood spreading in the cerebellar folia in patients with re-mote cerebellar hemorrhage (RCH)16 (Fig 16). RCH is usuallybenign, self-limited complication of supratentorial cran-iotomies. Temporal lobe resection for epilepsy, vascular

Fig 24.


Fig 25.

neurosurgery, or spinal surgery may be associated. Althoughthe exact mechanism accounting for RCH remains unclear lossof cerebrospinal fluid due to an interventional process lead-ing to cerebellar sagging, with a consequent occlusion of thebridging veins have been accused for.

17. “Empty delta” sign: Dural sinus thrombosis

The “empty delta” sign consists of a triangular areaof enhancement or high attenuation with a relatively low-attenuating center (filling defect of thrombus) on contiguousaxial contrast-enhanced CT17 (Fig 17). It is apparent in su-

Fig 26.

perior sagittal sinus thrombosis. The exact mechanism forthis appearance is uncertain, with possibilities including re-canalization around an organizing clot, enlargement of theperi-dural small veins, thickening of the dura with increasedenhancement.

18. “Caput medusa” sign: Developmental venous anomaly

The “caput medusa” sign is indicative of developmental ve-nous anomaly (DVA), and is identifiable on contrast-enhancedCT and MR18 (Fig 18). DVAs correspond to a network ofdilated, abnormal medullary veins with a radial distribution,

Fig 27.


Fig 28.

converging into a wide single drainage vein. This appearanceis reminiscent of Medusa, a gorgon of Greek mythology. An-giographically, the caput medusa appearance is seen only inthe venous phase. DVAs may be associated with cavernous an-giomas or one of the other types of CNS vascular malformations(i.e., arteriovenous malformation).

19. “Puff of smoke” sign: Moyamoya disease

The “puff of smoke” sign, characteristic of moyamoya dis-ease, is caused by the formation of collateral vessel networksfrom the progressive bilateral supraclinoid stenoses of the in-ternal carotid arteries. This sign, seen on cerebral angiographic

images, is a tangle of tiny vessels that look like a puff of smoke19

(Fig 19). Moyamoya, a name also used to describe this angio-graphic sign, comes from the Japanese meaning puff of smokeor hazy foggy appearance.

20. “Ivy” sign: Moyamoya disease

The “ivy” sign refers to tiny leptomeningeal high signal in-tensity along the cerebral sulci or on the brain surface in moy-amoya disease on unenhanced fluid-attenuated inversion re-covery (FLAIR) MR imaging20 (Fig 20). This sign initially wasdescribed for collateral vessels on contrast-enhanced T1W MRimaging.

21. “Hot nose” sign: Loss of cerebral blood flow; brain death

“Hot nose” sign refers to early and increased radiotracer ac-tivity in the nasopharyngeal region at nuclear scintigraphy.21

The phenomenon is a result of occlusion of the internalcarotid artery with flow rerouted to the nose via the externalcarotid artery. Note lack of flow to the cerebral hemispheresand abnormal increased nasopharyngeal activity (Fig 21;arrows).

C. Tumors and Tumor-like Lesions

22. Dural “tail” sign: Meningioma

The dural “tail” sign is seen on contrast-enhanced MR im-ages as a thickening of the enhanced dura mater that resem-bles a tail extending from the meningiomas22 (Fig 22). It wasinitially thought to result from direct invasion of the dura; how-ever, subsequent studies demonstrated it to be a more reactiveprocess. This sign, which had been described as highly specificfor meningiomas once, can also be seen in other extra- andintraaxial tumors that involve the dura mater.

Fig 29.


Fig 30.

Fig 31.

23. “Spoke-wheel” sign: Meningioma

The “spoke-wheel” sign refers to the typical angiographicappearance found in meningiomas. This sign corresponds tomultiple small arteries radially distributed from dominant feed-ing artery.23 This figure demonstrates spoke-wheel within themeningioma mass on the axial T2W MR image (Fig 23).

24. “Butterfly” sign: Glioblastoma multiforme, lymphoma, tume-factive demiyelinating lesion

“Butterfly” sign is most commonly described in glioblastomamultiforme (GBM) syndrome, and refers to the symmetric winglike extensions across the midline through the CC.24 This ap-pearance, however, is not pathognomonic of GBM (Fig 24A),

and has also been reported in lymphoma and tumefactive de-myelinating lesions (Fig 24B) which can involve CC.

25. “Soap bubble” sign: Dysembriyoblastic neuroepithelialtumor

Dysembryoplastic neuroepithelial tumor (DNET) is a be-nign tumor arising from the cortical or deep gray matter. DNETradiologically manifests as cortical masses that are hypointenseon T1- and hyperintense on T2W images (Fig 25) without sur-rounding vasogenic edema. The “soap bubble” appearance andbright rim on FLAIR images are characteristic.25 Calcificationand remodeling of the adjacent inner table of the skull may beseen.


Fig 32.

26. “Ice-cream” sign: Vestibular schwannoma

The schwannomas are the most common cerebellopontineangle (CPA) masses, while meningiomas are the second mostcommon. They expand the internal auditory canal (IAC), as amatter of their size. The tumor resembles classic “ice-cream” ap-pearance on axial imaging plane (Fig 26), while the componentinvolving IAC and extension into the CPA cistern constituteice-cream-cone and -scoop, respectively.26

D. Metabolic/Degenerative Disorders

Fig 33.

27. “The giant panda” sign: Wilson’s disease

This sign refers to a combination of signal intensity changesat midbrain on axial T2W MR imaging (Fig 27A). The patho-logic high signal intensity of tegmentum represents white faceof a panda while preserved intensity of red nuclei forms theeyes, pars reticulata the ears and superior colliculus representsthe nose.27 At caudal sections, increased signal within the dorsalpons is called “giant panda cub” in patients with Wilson disease(Fig 27B).

Fig 34.


Fig 35.

Fig 36.

28. “Eye of the tiger” sign: Pantothenate kinase-associated neu-rodegeneration (aka Hallervorden-Spatz syndrome)

This sign refers to symmetrical low signal intensity circum-scribing a central region of high signal intensity in the internalglobus pallidus on T2W MR images28 (Fig 28). The ring ofmarked hypointensity involving the globus pallidus on T2WMR images is due to excessive iron accumulation, and the cen-

Fig 37.

Fig 38.

tral high signal intensity is attributed to gliosis, increased watercontent, and neuronal loss.

29. “Tigroid pattern” or “leopard skin”: Metachromaticleukodystrophy

Metachromatic leukodystrophy (MLD) is an autosomal re-cessive disorder caused by a deficiency of the lysosomal enzyme


Fig 39.

Fig 40.

arylsulfatase. The diminished activity of arylsulfatase A enzymeaccounts for failure of myelin breakdown and reutilization,thus resulting in dysmyelination. On T2W MR imaging, MLDmanifests as symmetric confluent areas of high signal intensityin the periventricular white matter typically sparing the sub-cortical U fibers during the early stages.29 The sparing of theperivascular white matter within the centrum semiovale is re-sponsible for the characteristic “leopard skin” (Fig 29A) and“tigroid” (Fig 29B) pattern.

30. “Hot cross bun” sign: Multisystem atrophy-cerebellar type

“Hot cross bun” sign represents the changes of the brainstemin the multiple system atrophy of the cerebellar type on axialT2W MR imaging.30 The name derived from a sweet spicedbun baked by the Christian church and marked with a crosson the top. The sign is characterized by a cruciform pontinehyperintensity due to selective loss of myelinated transversepontocerebellar fibers and neurons, with preservation of thepontine tegmentum and the fibers of the corticospinal tract(Fig 30A and B). Note bilateral atrophy and increased T2 signalin the middle cerebellar peduncles.

31. “Tadpole” sign: Alexander disease

“Tadpole” sign is a quite peculiar feature: marked atrophyof the medulla oblongata and cervicothoracic cord with an in-tact pontine base, just like a “tadpole” on sagittal MR images31

(Fig 31A). Other imaging features of the Alexander diseaseare present in these patients, such as symmetrical frontopari-etal hyperintense lesions (Fig 32A) and significantly increasedmyoinositol concentrations in white matter lesions at MR spec-troscopy (TE = 30 msecond; Fig 32C).

32. “Penguin” or “hummingbird” sign: Progressive supranuclearpalsy

“Penguin” sign, also known as “hummingbird” sign refersto the atrophy of the midbrain tegmentum, with a relativelypreserved pons on midsagittal T1W images in patients withprogressive supranuclear palsy32 (Fig 32). The atrophy of themidbrain results in a profile of the brainstem in which the pre-served pons forms the body of the bird, and the atrophic mid-brain the head, with beak extending anteriorly toward the opticchiasm. Note preservation of medulla width which differs fromthe above “tadpole” sign.

33. “Morning glory” sign: Progressive supranuclear palsy

“Morning glory” sign refers to peculiar atrophy of the mid-brain characterized by a concavity of the lateral margin ofits tegmentum on the axial images.33 Also, note the markedincrease in signal intensity of the periaqueductal gray region(Fig 33).

E. Infection and Demyelinating Disease

34. “Trident” sign: Central pontine myelinolysis

Central pontine myelinolysis (CPM), also known as osmoticdemyelination, is an acute demyelinating condition of the brain-stem and is a recognized complication of the rapid correction ofchronic hyponatremia. Symptoms of CPM include tetraplegia,pseudobulbar palsy, and acute changes in mental status lead-ing to coma or death without intervention. Typically, tridentshaped central pontine hyperintense signal abnormality revealson T2W MR images.34 The peripheral fibers (ventrolateral lon-gitudinal fibers and corticospinal tracts) as well as the periven-tricular and subpial regions are typically spared (Fig 34A andB).


35. “Horse-shoe” sign: Multiple sclerosis

The enhancement pattern in multiple sclerosis or tumefac-tive demyelinating lesions is not uncommonly in the form of anopen ring (“horse-shoe” shaped) enhancement, with the incom-plete portion of the ring facing the cerebral cortex35 (Fig 35).The enhancing segment of the ring is thought to represent thezone of active demyelination (leading edge) accordingly favor-ing the white matter side of the lesion. The nonenhancing cen-tral part represents a more chronic phase of demyelination.Given the size of the lesion, accompanying edema and masseffect are disproportionately less than expected.

36. “Onion-skin” sign: Balo’s concentric sclerosis

Balo’s concentric sclerosis presents a peculiar pattern of con-centric lamellae of myelin and demyelinated layers around acentral focus (“onion-skin”)36 (Fig 36). Balo’s concentric scle-rosis may occur as an isolated phenomenon or precede thedevelopment of multiple sclerosis.

37. “Hockey-stick” sign: Creutzfeldt-Jacob disease

“Hockey-stick” sign refers to symmetrical pulvinar and dor-somedial thalamic nuclear hyperintensity in patients with vari-ant Creutzfeldt-Jacob disease (vCJD). This sign is highly sensi-tive and specific for vCJD37 (Fig 37).

38. “Water-Lily” sign: Hydatid cyst

Hydatid disease of CNS is rare and most frequently supraten-torial, involving the territory of the MCA. The signal intensityof the cysts is identical to CSF unless infected. Hydatid cystsare classified into five types, and these can be determined byany imaging modality. In type 2 hydatid cyst, detachment ofinner germinal layer results in a floating membrane with char-acteristically convex serpiginous margin on the surface of theremaining cyst, creating an appearance known as “water-lily”sign or “floating lily” sign38 (Fig 38).

F. Others

39. Reverse cupping sign: Increased intracranial pressure

The globe at its junction with the optic nerve can be indented(reverse “cupping”) by the transmitted raised intracranial pres-sure, clinically manifested as papilledema39 (Fig 39).

40. “En coup de sabre”: Parry-Romberg syndrome/linear sclero-derma

Linear scleroderma appears as an indented, vertical, color-less, line of skin on the forehead. The condition is described bythe French word “en coup de sabre” or “sword stroke.” Parry-Romberg syndrome, also known as progressive facial hemiatro-phy, overlaps with a condition known as linear scleroderma andis a neurocutaneous syndrome. But, the relationship betweenthe two entities is still controversial. Neurological involvementis frequently described in Parry-Romberg syndrome, includingmigraine, facial pain, and epilepsy. The focal linear atrophy ofthe skin and subcutaneous tissues can be seen on MR images40

(Fig 40).

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power of the metaphor: forty signs on brain imaging

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