Journal of Clinical Ophthalmology and Research

COMMISSIONED ARTICLE
Year
: 2013  |  Volume : 1  |  Issue : 2  |  Page : 101--106

Interpretation of magnetic resonance imaging of orbit: Simplified for ophthalmologists (Part II)


Barun K Nayak1, Savari Desai1, S Maheshwari2, Divya Singh3, Sanjay Sharma3,  
1 Department of Ophthalmology, P D Hinduja National Hospital and MRC, Mumbai, India
2 Department of Radiodiagnosis, P D Hinduja National Hospital and MRC, Mumbai, India
3 Department of Radiodiagnosis, R P Centre for Ophthalmology Sciences, AIIMS, New Delhi, India

Correspondence Address:
Barun K Nayak
Department of Ophthalmology, P D Hinduja National Hospital and MRC, Mumbai
India

Abstract

The basics of orbital magnetic resonance imaging (MRI) has been discussed in the previous issue. This article is in continuation of the previous article, and deals with the systematic approach towards the diagnosis of various orbital pathological lesions. It starts with the concept of various compartments in the orbit with their boundaries, followed by the mention of different lesions occurring in those compartments. The representative pictures of MRI orbit is also being provided with their main features on MRI of some commonly occurring pathologies of orbit. The purpose of this article is to impart the skill amongst ophthalmologists of interpreting orbital MRI.



How to cite this article:
Nayak BK, Desai S, Maheshwari S, Singh D, Sharma S. Interpretation of magnetic resonance imaging of orbit: Simplified for ophthalmologists (Part II).J Clin Ophthalmol Res 2013;1:101-106


How to cite this URL:
Nayak BK, Desai S, Maheshwari S, Singh D, Sharma S. Interpretation of magnetic resonance imaging of orbit: Simplified for ophthalmologists (Part II). J Clin Ophthalmol Res [serial online] 2013 [cited 2022 Aug 12 ];1:101-106
Available from: https://www.jcor.in/text.asp?2013/1/2/101/112178


Full Text

In the previous issue, we have described the basics of orbital magnetic resonance imaging (MRI) and the appearance of normal anatomical structures on orbital MRI. [1] A proper, understanding of orbital pathology is essential for diagnosing various lesions on the basis of orbital MRI. The purpose of this presentation is to outline a systematic approach while interpreting the orbital MRI films, to be followed by providing the MRI images of some of the common lesions of orbit.

Any mass lesion in orbit can produce two types of effects as described by Rootman J. The functional effects, which can be in the form of the motor disturbances, sensory disturbances, and the secretory disturbance of orbital structure. These are mainly responsible for the clinical presentation. Secondly, the mass effects, which can be in the form of either shifting of structures (positive effect) or enlargement of space as a result of pressure or cicatrization (negative effect). This can also produce symptoms sometimes. However, the MRI will always highlight the mass effect accurately apart from the nature and characteristics of the mass itself. Hence, the final conclusion should be drawn only after correlating the MRI findings with the clinical picture.

 Lesions of orbit



The lesions can start de novo in orbit and periorbital tissue or may be a reflection of systemic disease or secondary's from the tumor of the other parts of the body. The various pathologies of orbit can fall in one of the five broad categories mentioned below: [2]

InflammatoryNeoplasticStructural abnormality (acquired or congenital)VascularDegenerations and depositions

 Inflammatory



This constitutes about 3/5 th of all the orbital pathologies out of which about 85% is due to the thyroid ophthalmopathy. Inflammatory condition can be divided into acute, subacute or chronic. The examples of acute conditions are infective cellullitis, non-specific idiopathic inflammation (pseudotumor), acute ocular inflammation (uveitis, keratitis, scleritis), sudden event in pre-existing lesion (hemorrhage in lymphangioma), and fulminant neoplasm (chloroma, rhabdomyosarcoma, metaplasia). The subacute category includes thyroid orbitopathy, infective cellulitis (fungal), specific or non-specific idiopathic orbital inflammation (granuloma), primary ocular inflammation (scleritis, uveitis), collagen vascular disease, rapidly developing (fulminant) malignancies. The chronic inflammatory conditions can be due to primary and secondary neoplasia, thyroid, lymphoproliferative disorders, collagen vascular disease, idiopathic sclerosing inflammation, and rare diseases like amyloidosis.

 Neoplastic



This constitutes about 1/5 th of all orbital lesions. These can be benign or malignant.

 Structural



It can be congenital (eg., Crouzon's disease, craniofacial dysostosis, maxillary hypoplasia, facial asymmetry) or acquired (Post-traumatic: Direct physical, thermal, chemical, radiation induced). Some other lesions can be in the form of cysts (dermoid, implantations, lacrimal, mucocoele) and ectopias.

 Vascular



Character of flow (hemodynamics) will vary based on the type of lesion. Non-obstructive vascular lesion on the arterial side can have high or low flow (such as tumors, malformations and shunts). Venous malformation can be either distensible or non-distensible. There may be arterio-venous abnormalities (dural fistula, arterio-venous malformations), venous lymphatic (lymphangioma), arterio capillaries (Sturge Weber, hereditary hemorrhagic telangiectasia). Furthermore, there may be purely obstructive arterial or venous lesions. Infantile capillary hemangiomas are high-flow tumors on the arterial side. Cavernous hemangioma is a lesion with low arterial flow. Congenital arterio venous (AV) malformation and acquired AV fistulas may be high or low flow based on the large or small shunt vessels.

 Degeneration and depositions



These can be atrophy, cicatrization, or depositions (progressive myopathy, amyloid deposition, and linear scleroderma).

 Compartments of orbit



For proper diagnosis of pathologies on MRI, we must have proper knowledge of various compartments in the orbit. Each compartment can have a limited type of lesions due to the presence of different types of tissue in each compartment. However, sometimes the lesion may extend in more than one compartment or may be even diffuse involving multiple compartments.

The various compartments for this purpose can be divided as follows: [3]

Intraconal spaceExtra ocular musclesExtraconal spaceSubperiosteal spaceLacrimal glandOcularPreseptal space

We will describe the boundaries of various spaces and the common lesions found in that space. Although axial, coronal and sagittal cuts are always used for studying proper orientation of various lesions in orbit, we will also mention the most suited cuts for a particular compartment.

 Intraconal space



This is the space inside the four recti muscles and their connections (muscle cone). A very important structure, which lies inside this space, is the optic nerve and its sheath. This can be considered as a separate compartment as its lesions are different than the rest of the intraconal space. Optic nerve sheath is the extension of meninges and has the same characteristics. The space between optic nerve and the sheath is the subarachnoid space. The optic nerve has S shaped course in the sagittal plane and parasagittal planes are used to study the optic nerve. However, the diameter of the optic nerve and surrounding subarachnoid space is best studied in the coronal planes. The common lesions here are optic neuritis, fracture of orbital apex with bleeding, perineuritis and optic glioma. Other conditions are optic nerve sheath meningioma, metastases, and sarcoidosis.

The rest of the intraconal space can be best studied in the coronal plane. Common lesions are cavernous hemangioma, inflammatory pseudotumor, and varix. Other lesions include lymphangioma, neurofibromatosis, enlarged vein in AV fistulae and metastases. Rarely, lymphoma and capillary hemangioma may also occur in this space.

 Extraocular eye muscles



Primary evaluation is performed in the coronal sections and both side should be studied together to know the enlargement of the muscles. However, the axial or parasagittal cuts depict the muscles in the longitudinal extent and it is essential to establish the involvement of tendon and muscle belly together or only the muscle belly. Thyroid myopathy involves only the muscle belly and spares the tendon. Common conditions affecting muscles are thyroid orbitopathy, myositis and lesions with the pseudotumors. Other rare lesions are lymphoma, rhabdomyosarcoma, AV fistula, and trauma.

 Extraconal space



It is the space between the muscle cone and the periosteum of the orbital wall and anteriorly limited by orbital septum. The best plane to visualize this space is coronal sections. Lymphoma and capillary hemangioma are common lesions whereas rhabdomyosarcoma, neurofibroma and metastases are rare lesions of this space.

 Subperiosteal space



This is the space between the periosteum and the bony wall of the orbit. All cuts are important based on the location of the lesion. This space can be affected by lesions originating from the surrounding structures, as well. Common lesions are mucocoele, orbital fractures, subperiosteal abscess, and tumors of paranasal sinuses, dermoids, metastases, osteomas, epidermoids, and meningiomas. Other rare lesions can be fibrous dysplasia, plasmacytoma, Wegener's granulomatosis, cholesterol cysts, and Paget's disease. Soft-tissue damage can be assessed in traumatic cases.

 Lacrimal gland



The coronal sections provide the best assessment of lacrimal gland, which is situated in upper outer quadrant of orbit. Epithelial lesions can be benign (pleomorphic adenoma) or malignant (pleomorphic adenocarcinoma). Non-epithelial tumors are lymphomas and inflammatory pseudotumors.

 Ocular



Most of the lesions of the globe can be diagnosed by direct examination or other investigations such as ultrasound. MRI is useful in diagnosis of uveal melanoma, hemangioma, metastases, and infantile retinoblastoma.

 Preseptal space



This is the space in front of orbital septum in the upper and lower lids. MRI is rarely ordered for diagnosis of lesions of this space, but it can depict the extent and infiltration of orbital septum. The common conditions are inflammatory, xanthelasma, tumors of limited malignant potential. Rare conditions are lymphomas, capillary hemangioma, and metastases.

 Steps for Reading an MRI film



Place the MRI film in a viewing boxWhat is the abnormality and characteristics of lesion in T1 weighted images?What is the abnormality and characteristics of lesion in T2 weighted images?What is the location (compartment) of the lesion?What is the extent of the lesion?What are the morphologic characteristics (such as well-circumscribed or diffuse, mottled or uniform, fluid space etc.)?Review special sequences such as FLAIR, STIR [1] Is contrast done - if yes what is the nature of the lesion post contrast?Correlate clinically so as to be able to have differential diagnosis.

We will now be describing MRI of some of the pathological conditions [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] that we encounter frequently. Understanding and interpreting these images has been kept very simple, as only the selected relevant cuts are provided here with pointers. However, we encourage the readers to note and analyze the findings themselves before reading the legends provided with the images.{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}

A detailed discussion on the images is out of the scope of this article. Interested readers are advised to consult radiology books with an interest in orbital imaging for further understanding. A simple way to improve your skill will be, to study all the MRI films of the patient in concern. Note down your own findings in detail after studying the films. Thereafter, take out the report provided by the radiologists, review the full report including the conclusion. Compare your own noted findings with the radiologists report and mark the discrepancies between the two reports This will help to improve your own analytical skill and confidence. After a couple of months you will become an expert in reading the MRI of the orbit. The purpose of this write up is to initiate the interest toward the interpretation of orbital MRI amongst the ophthalmologists, and hope it serves the purpose.

References

1Nayak BK, Desai S, Maheshwari S. Interpretation of magnetic resonance imaging of orbit: Simplified for ophthalmologists (Part I). J Clin Ophthalmol Res 2013;1:29-35.
2Rootman J. Disease of Orbit: A Multidisciplinary Approach. Philadelphia: Lippincott Williams & Wilkins; 2003. p. 35-52.
3AJ, Kazi I, Felix R. Magnetic resonance imaging of orbital tumors. Eur Radiol 2006;16:2207-19.