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 Table of Contents  
MAJOR REVIEW
Year : 2016  |  Volume : 28  |  Issue : 2  |  Page : 103-111

Guidelines for imaging in Neuro-ophthalmic and Orbital disease


1 Department of Ophthalmology, Alexander Eye Centre, Kochi, Kerala, India
2 Department of Radiology, Lourdes Hospital, Kochi, Kerala, India

Date of Web Publication20-Mar-2017

Correspondence Address:
Thomas A Varghese
Consultant Ophthalmologist, Alexander Eye Centre, Kochi - 682 024, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/kjo.kjo_5_17

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  Abstract 


Neuroimaging has progressed from plain X-ray to magnetic resonance imaging, noninvasive angiography, and special sequences. Utilization of the appropriate investigation can save the sight and sometimes life of the patient. This article attempts to guide the ophthalmologist in choosing the most suitable modality in the different clinical scenarios.

Keywords: CT angiography, computed tomography, magnetic resonance angiography, magnetic resonance imaging


How to cite this article:
Varghese TA, Varghese A. Guidelines for imaging in Neuro-ophthalmic and Orbital disease. Kerala J Ophthalmol 2016;28:103-11

How to cite this URL:
Varghese TA, Varghese A. Guidelines for imaging in Neuro-ophthalmic and Orbital disease. Kerala J Ophthalmol [serial online] 2016 [cited 2019 Sep 20];28:103-11. Available from: http://www.kjophthal.com/text.asp?2016/28/2/103/202481




  Introduction Top


Many a time it is the ophthalmologist who is confronted with clinical situations that could be a part of a larger problem.[1],[2] The changing times and rapid advances in imaging technology requires the ophthalmologist to keep up to date.


  Modalities Available Top


Magnetic resonance imaging

Magnetic resonance imaging (MRI), first tried on a human in 1977, is the modality of choice for brain and orbit imaging due to better soft tissue discrimination, superior resolution, and multiplanar capability with the added advantage of no radiation exposure. Machines of varying magnetic field strength from 0.3 Tesla upwards are available. Resolution improves with increasing field strength, with machines of 1.5 T and above giving high quality images. The protons of hydrogen in water molecules have their own magnetic field and are randomly aligned in the body in the resting state. When placed in an external magnetic field (as that of an MRI scanner), they align in a parallel or antiparallel direction. A radiofrequency (RF) pulse will excite the protons and cause them to change direction. MRI signal is obtained from different relaxation times (time taken for excited proton to return to resting state) of tissues. The signal is influenced by the presence of other materials and impurities in the tissues. T1 images show bright signal from tissue with rapid relaxation (fat, melanin, and subacute hemorrhage) [Figure 1]. It is best for anatomy.[3] T2 images show bright signal from tissues with slow relaxation (CSF, vitreous humor, edema, some stages of hemorrhage) [Figure 2]. It is best to highlight the site of pathology. MRI is especially useful in identifying ischemia, inflammation, and tumors [Figure 3] and [Figure 4].
Figure 1: MRI -Axial T1 Image – Normal scan - Fat is bright, CSF and vitreous dark

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Figure 2: MRI Axial T2- Normal scan- CSF and Vitreous bright, fat is less bright

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Figure 3: 73 year old female presented with gradual loss of vision left eye over 1 year. CT scan done 2 months prior was reported as normal

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Figure 4: Examination showed a junctional scotoma with loss of central vision in the right eye. MRI with contrast showed a sphenoid meningioma at the junction of right optic nerve with chiasma

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There are some special sequences in MRI which are very useful. Fat suppression technique highlights the intraorbital structures, which are normally surrounded by the bright signal of orbital fat [Figure 5] and [Figure 6].[4] Fluid-attenuated inversion recovery (FLAIR) sequence, done routinely, is the most sensitive to pick up pathology [Figure 7].[5] Diffusion-weighted imaging (DWI) is very sensitive in acute ischemia (changes appear within minutes of onset) [Figure 8].[6],[7],[8],[9],[10]
Figure 5: 72 year old presented with sudden loss of vision right eye. Examination showed right RAPD with normal fundus.MRI without fat suppression shows swollen right optic nerve

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Figure 6: MRI with fat suppression (FS) shows CSF around the left optic nerve but not the right indicating right optic nerve swelling behind the globe – suggestive of right posterior ischaemic optic neuropathy (PION)

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Figure 7: 19 yr old male with sudden diminution of vision right eye. MRI Sagittal FLAIR- multiple fingerlike white matter lesions in pericallosal area- Dawson's fingers- diagnostic of MS

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Figure 8: 68 yr old male with sudden giddiness and loss of vision. Emergency MRI revealed bright signal in right occipital parenchyma on DWI [Diffusion Weighted Imaging] images

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Apparent diffusion coefficient (ADC) obtained by the software helps in confirming true ischemia [Figure 9]. Susceptibility-weighted imaging (SWI)(a gradient echo sequence) detects hemorrhage and calcification and is a pointer to vascular disorders such as aneurysms, cavernous hemangioma, and arteriovenous malformations (AVM)[Figure 10] and [Figure 11]. Special situations warrant MR angiography [Figure 12], which utilizes the fast flow of blood in arteries, and hence, maps arteries without use of intravenous contrast – a definite advantage over conventional and CT angiography.[11],[12] MR venography (MRV)[Figure 13]maps the major dural venous sinuses and can be done without contrast medium.[13] Doubtful thrombosis can be verified with intravenous contrast. Gadolinium, the contrast used with MRI, can be used to ascertain the enhancement of masses and vessels [Figure 14] and [Figure 15]. It can be used despite history of allergy to Iodine compounds.
Figure 9: ADC-[apparent diffusion coefficient ] dark area in corresponding region.Confirming acute infarct

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Figure 10: 64yr female – gradual proptosis. MRI- t-2 axial and coronal fat saturation images with rt orbital mass lesion of inhomogenous nature

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Figure 11: Orbital Cavernous Haemangioma. s/o orbitalcavernoishaemngioma

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Figure 12: MRA [MR angiography without contrast] showing no flow in distal part of right posterior cerebral artery

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Figure 13: 26 yrvfemalepost partum headache . O/E papiloedoema MRI–MRV[ post contrast] shows narrowing of rt transverse sinus due to thrombosis

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Figure 14: MRI plain showing lesion along right petrous ridge anterior to right side of pons

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Figure 15: MRI contrast- enhancing lesion along rt petrous ridge with dural tail sign- Diagnosis -petrous meningioma

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Common indications for imaging in neuroophthalmology [14],[15],[16][Table 1]are cranial nerve palsies,[17] [Figure 16], [Figure 17], [Figure 18], disc edema,[18],[19][Figure 19], [Figure 20], [Figure 21], [Figure 22], visual loss [Figure 23], field defect [Figure 24], Horner's syndrome,[20] [Figure 25], nystagmus [Figure 26], hemifacial spasm, and internuclear ophthalmoplegia.
Table 1: Recommended Imaging in Neuro-ophthalmology

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Figure 16: 82 year old lady presenting with drooping of right eyelid. Examination showed pupil involving right 3rd nerve palsy. MRI with MRA showed bilateral internal carotid artery aneurysm within the cavernous sinus

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Figure 17: 35 year old female presented with c/o intermittent double vision for 2 weeks. Examination showed DVD and reduced sensation of 1st and 2nd divisions of trigeminal nerve. MRI showed an Acoustic neuroma

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Figure 18: 4yr female child presented with multiple cranial nerve palsies.[6+7+8] MRI-4 th ventricle mass -causing anterior compression of pons.. medulloblastoma

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Figure 19: 28 year old female with h/o recent weight gain , presented with c/o headache

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Figure 20: Examination showed bilateral disc oedema with weight 110kg. MRI T2 Axial and Sagittal showed features of IIH- indentation of globe, tortuous optic nerves with widened perioptic spaces and empty sella

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Figure 21: 35 year old female on oral contraceptive pill and recent episode of diiarrhoea ( hypercoagulable state) presented with headache and double vision. Examination showed sixth nerve palsy with disc oedema. MR Venography showed thrombosis of superior sagittal sinus

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Figure 22: Following emergency thrombolytic treatment, MRV shows improved filling of SSS

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Figure 23: 15 year old girl presented with c/o noticing poor vision in left eye for 1 week. Examination showed left reduced visual acuity and RAPD with pale disc, right normal. MRI showed left optic nerve glioma

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Figure 24: 30 year old female with h/o infertility treatment presented with c/o gradual decreasing of vision both eyes. Field test showed ' pie on the sky' field defect. MRI showed a pituitary macroadenoma

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Figure 25: 75 year old male smoker presented with drooping of left eyelid for 1 month. Examination showed Left Horner's syndrome. CT with contrast showed mass in left lung apex infiltrating root of neck with rib destruction (Pancoast's tumour)

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Figure 26: 38 year old man presented with c/o of images vibrating for 2 weeks. Examination showed convergence retraction nystagmus. MRI Sagittal showed a porencephalic cyst in the dorsal midbrain

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The usual indications for orbital imaging are orbital cellulitis, orbital pseudotumour, thyroid ophthalmopathy, orbital masses, caroticocavernous fistula, and trauma [Table 2].
Table 2: Recommendation for imaging in orbital pathology

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Computed tomography

Computed tomography (CT) scan, when first introduced in 1972, revolutionized the scene of neuroimaging. An X-ray tube rotates around the part scanned and an array of detectors measure the signal from the attenuated X rays exiting the body. Hounsfield units (HU) help to standardize the density of the whole range of tissue types. [Air:-1000HU, Fat:-100HU, Water (CSF) O HU, Muscle: +20 HU, Bone: +1000 HU].

With the emergence of spiral CT, imaging of head and orbit in multiple planes in greater detail is possible compared to earlier single slice scanners. Spiral CT systems enable complete coverage of the field, quicker scan time, and additional diagnostic information due to image reconstruction. Emergency CT scanning is done in cases of suspected stroke [Figure 27]. AII spiral systems from 16 slice upwards (systems range 16–512 slices) can deliver high quality reconstructed images in multiple planes, the resolution improving exponentially with increasing slice number. Cuts of 5 mm and 1 mm are done as routine. Software of the machine helps in displaying images in different settings for better bone and soft tissue details. In trauma and postoperative cases, 30 bone reconstructions are particularly useful.[21] CTA (CT angiography) very often reveal aneurysms or AVM [Figure 28].[22] Reconstructed images help in explaining to patient and improves compliance. CT is preferred in trauma and suspected bony tumors due to better imaging of facial bones and orbital canal [Figure 29] and [Figure 30]. The indications for CT in neuroophthamology are specific [Table 3].
Figure 27: 75 year old man presenting with c/o sudden blurring of vision and giddiness. Examination showed left homonymous hemianopia. Plain Axial CT showed right occipital infarct

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Figure 28: 46 yr male with hypertension presented with headache and drooping of left eyelid. Examination showed left pupil involving 3rd nerve palsy. CT Angiogram showed wide necked saccular aneurysm at the origin of left Posterior Communicating artery

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Table 3: Indications for CT

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Figure 29: 45 year old female presenting with blurring of vision left eye for 2 months. Examination showed left proptosis with left disc oedema. CT scan done - as bony lesion suspected - showed Osteoma

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Figure 30: 40 year old female with c/o blurring of vision LE for 3 weeks. Eccentric proptosis and fullness of left temporal fossa on examination – CT scan done as bony lesion suspected - showed Fibrous dysplasia

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Intravenous contrast medium will further increase the detail and accuracy of imaging. CT contrast materials are iodinated compounds which will attenuate X-rays, and hence, make it much brighter on the image. Hence, any structure with more vascularity will get more of the intravascular contrast. Contrast allergy and renal failure precludes the use of iodinated contrast. Patients with history of allergy, asthma, and diabetes mellitus are more likely to develop allergy to the contrast medium. A major disadvantage of CT is ionizing radiation exposure. It should be judiciously used in children and the young.

Digital subtraction angiography

Digital subtraction angiography (DSA) is specifically required in cases of vascular pathology including aneurysms, and arteriovenous fistulas. It involves use of X-rays in the catheterization laboratory. These conditions will often require DSA in addition to CT angiography and MRA.[23] Disadvantage being it is an invasive procedure and require large volume of intravenous contrast due to need for repeated injections. High radiation exposure is also inevitable. There is the possibility of some complications as it involves manipulation of an inserted intravascular catheter. A stepwise decision should be made as to what is the ideal imaging in an individual case [Table 4]. A sound clinical evaluation should be the foundation on which imaging is based.
Table 4: Flowchart for deciding which imaging modality and sequence to use

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  Conclusion Top


It is essential that the ophthalmologist chooses the appropriate investigation in each clinical situation. MRI is the investigation of choice because of it greater resolution and differentiating capability. There are a handful of situations where CT Is still preferred. The key to diagnosis are good clinical history, meticulous examination, requisition of a tailored/appropriate investigation, and communication with the radiologist. The relevant clinical findings and approximate location of lesion are crucial for the radiologist to contribute best to the case.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Kim JD, Hashemi N, Gelman R, Lee AG. Neuroimaging in Ophthalmology. Saudi J Ophthalmol 2012;26:401-7.  Back to cited text no. 15
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22], [Figure 23], [Figure 24], [Figure 25], [Figure 26], [Figure 27], [Figure 28], [Figure 29], [Figure 30]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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