Ординатура / Офтальмология / Английские материалы / Surgical Atlas of Orbital Diseases_Mallajosyula_2009

disorders. Other important secondary orbital lesions that cause bilateral involvement, though not necessarily at the same time, include squamous cell carcinoma of the conjunctiva associated with xeroderma pigmentosum, and neglected retinoblastoma. The most common cause of unilateral proptosis in children is dermoid cyst, followed by hemangiomas. Rhabdomyosarcoma is the most common malignant lesion of pediatric age group. In adults, the most common cause of proptosis, either unilateral or bilateral is thyroid associated orbitopathy. Nonspecific orbital inflammation, granuloma (especially fungal granuloma involving frontoethmoid sinuses) and lymphomas are the other common bilateral lesions of orbit. However, the frequency of these conditions can change from place to place, depending upon the disease patterns of those areas. For example in India we see a lot of cases of

orbital myocysticercosis, which many of you in the western world might not have come across. Similarly, we rarely come across Wagener's granulomatosis, which is fairly common in the west. The disease presentations also can vary in different parts of the world. When compared to the west, we in South India very rarely come across severe thyroid orbitopathy. The incidence of infection due to tuberculosis is on the rise because of HIV. So is the case with lymphoma. Thus the spectrum of orbital diseases is varied in different parts of the world (Table 2.1). With a good knowledge of the disease patterns of the region and a good clinical work-up, a reasonable clinical diagnosis can be made most of the times. Advances in investigative modalities like imaging (CT, MRI) ,histopathology (FNAC, IHC, Squash) come to our aid to make a very accurate diagnosis, which goes a long way in managing the case.

Evaluation of a Case of Proptosis

Name: Age: Sex:

Occupation: Address:

Regn. Number

Presenting complaints:

History of present illness:

Proptosis : Onset and Progression Defective vision:

Double vision: Pain scoring: Trauma history:

Other history: (circle the one relevant): Thyroid disease (Wt loss/gain, tremors, neck swellings, palpitations, others), sinusitis, aggravation with respiratory infections, others .

Treatment history

Past History:(Circle the ones relevant)

Family history:

Personal history:

General systemic examination:(circle the ones relevant)

Pulse:

BP:

RR:

Temperature:

CVS:

Respiratory System: Abdominal Examination: ENT Examination:

BIBLIOGRAPHY

1.Ben Simon GJ, Yoon MK, Atul J, Nakra T, McCann JD, Goldberg RA. Clinical manifestations of orbital mass lesions at the Jules Stein Eye Institute, 1999-2003. Ophthalmic Surg Lasers Imaging. 2006;37(1):25-32.

2.Dunsky IL. Normative data for Hertel exophthalmometry in normal adult black population. Optom.Vis Sci 1992;69:562-4.

3.Fledelius HC, Stubgaard M. Changes in eye position during growth and adult life as based on exophthalmometry, interpupillary distance, and orbital distance measure-ments.Acta Ophthalmologica. 1986;64:481-6.

4.Gladstone JP. An approach to the patient with painful ophthalmoplegia, with a focus on Tolosa-Hunt syndrome. Curr Pain Headache Rep. 2007;11(4):317-25.

5.Grove AS Jr. Modern examination methods of orbital disease. Orbital radionuclide examinations. Trans Am Acad Ophthalmol Otolaryngol. 1974;78(4):OP587-98.

6.Knudtzon K On exophthalmometry; the result of 724 measurements with Hertel’s exophthalmometer on normal adult individuals. Acta Psychiatr Neurol. 1949;24(3-4):523-37.

7.Kolasa P, Kaurzel Z. Post-traumatic pulsating exophthalmus coexisting with congenital carotid-cavernous fistula. Neurol Neurochir Pol. 2001;35 Suppl 5:58-63.

8.Krayenbühl HA. Unilateral exophthalmos. Clin Neurosurg. 1966;14:45-71.

9.La Mantia L, Erbetta A, Bussone G. Painful ophthalmoplegia: an unresolved clinical problem. Neurol Sci. 2005;26 Suppl 2:s79-82.

10.Malhotra R, Wormald PJ, Selva D. Bilateral dynamic proptosis due to frontoethmoidal sinus mucocele. Ophthal Plast Reconstr Surg. 2003;19(2):156-7.

11.Meyer DR. Compressive optic neuropathy. Ophthal-mology. 2007;114(1):199.

12.Miller NR. Neuro-Ophthalmology of orbital tumors. Clin Neurosurg. 1985;32:459-73.

13.Rootman J. An approach to diagnosis of orbital disease. Can J Ophthalmol 1983;18:102-7.

14.Shields JA, Shields CL, Scartozzi R. Survey of 1264 patients with orbital tumors and simulating lesions: The 2002 Montgomery Lecture, part 1. Ophthalmology. 2004;111(5):997-1008.

15.Sugawara Y, Harii K, Hirabayashi S, Sakurai A, Sasaki T. A spheno-orbital encephalocele with unilateral exophthalmos. Ann Plast Surg. 1996;36(4):410-2.

16.Weinstein JM, Van Gilder JC, Thompson HS. Pupil cycle time in optic nerve compression. Am J Ophthalmol. 1980;89(2):263-7.

“Proptosis is a Pandora's box” was the most often quoted sentence in the past, and it was rightly so, since "surprises on the operation table" were quite frequent. The surprises could be in the form of pathology, localization and extent of the lesion. These problems were too frequent for the occasional orbital surgeon. Hence, many a time in the past it was the team effort—a team of neurosurgeon and ophthalmologist—that used to perform surgery on every case of proptosis. Advances in imaging techniques have changed the scenario completely. With the advent of CT scan and later MRI we know the exact location of the lesion, the nature of the lesion (tumor or a cyst, encapsulated/ infiltrating, highly vascular /less vascular, benign/malignant/ metastatic). We can also very accurately predict the histological nature of the lesion like glioma of the optic nerve/meningioma of the optic nerve sheath/ sphenoid ridge meningioma/ thyroid orbitopathy/ cavernous hemangioma/ lymphangioma/ myocysticercosis/ myositis/lymphoma, etc. Hence the surprises in proptosis were very rare now. After a thorough clinical evaluation and imaging with CT, most often we know the nature and location of the lesion, which enables us to manage proptosis in a systematic way. We strongly believe that the advances in imaging technologies have not only made the diagnosis and management of proptosis more scientific, they have revived interest in the subspecialty of orbital services.

The globe, conjunctiva and optic disc are the orbital structures amenable for direct examination. Pathology involving the rest of the orbital structures

needs imaging studies for optimal evaluation. Several imaging techniques such as plain radiography, ultrasound, color Doppler, computed tomography (CT) and magnetic resonance imaging (MRI) are available for imaging orbital pathology. Each technique has its own advantages and disadvantages, and the information obtained from these studies is often complementary.

Plain radiography has been the only investigation available for orbital imaging for most of the last century. Now, CT and MRI have largely replaced radiography, and skull X-rays are now performed only in selected cases of facial fractures and to screen for intraocular metallic foreign bodies before an MR examination. Sonography is used largely in the evaluation of intraocular structures. Large mass lesions in the orbit can also be visualized and characterized on sonography. Ultrasound combined with Duplex Doppler plays an important role in the noninvasive evaluation of vascular pathology involving the orbit. It can differentiate low flow lesions from high flow arteriovenous malformations. Though sonography is convenient and non-invasive, it suffers from limitations in the form of suboptimal visualization of the posteriorly placed structures, nonvisualization of intracranial pathology and need for expertise on part of the examiner.

The most widely used radiological investigation for evaluation of the orbit is CT scan. It has the advantages of being widely available, fast, inexpensive and relatively easy to interpret. The technique is based on differential attenuation of X-rays by tissues, where denser tissues attenuate

more X-rays. Tissues can be characterized by their attenuation values (also called Hounsfield units (HU) - named after the inventor of CT). The retro-orbital fat imparts a natural contrast that aids in delineation of normal anatomy as well as pathology. On the Hounsfield unit scale, air is defined as –1000 HU, pure water as 0 HU, and dense cortical bone as +1000 HU. Retro-orbital fat usually measures –120 to –50 HU, cerebrospinal fluid measures 0 to +10 HU, extraocular muscles measure +40 to +50 HU and brain measures +35 to +45 HU. CT scans of the orbit are best obtained before and after intravenous administration of iodinated contrast medium. Thin sections (2-3 mm) are required to delineate the pathology and differentiate it from the normal orbital structures. Imaging in both axial and coronal planes may be required to optimally evaluate orbital pathology. The images can be viewed in different window settings to evaluate structures such as the soft tissues on bony structures.

Modern day spiral CT and multidetector CT technology permit acquisition of the imaging data as a volume, within a few seconds so as to minimize movement artifacts. It is now possible to acquire images in several phases during and after intravenous administration of contrast medium, that may be instrumental in diagnosing vascular and other similar abnormalities of the orbit. In addition, post processing of spiral CT data yields extremely high resolution multiplanar reconstructions and 3- dimensional images, without the need for additional exposure to radiation. CT scan images are taken with soft tissue windows (to study the details of the globe and the soft tissue lesion) and bone windows (give the details of the bone).

Though CT scan is considered as the work-horse of orbital imaging, it suffers from several disadvantages such as relatively low tissue contrast as compared to MRI, and severe degradation of image quality by dental fillings. Dose of radiation to the lens, which is most sensitive organ in the body to radiation exposure, is a concern.

Unlike radiography and CT scan, MR imaging does not use ionizing radiation. Image production in MRI is based on measurement of relaxation properties of protons after excitation with radiofrequency energy. By altering the parameters of data acquisition, we can obtain several image

Imaging a Case of Proptosis: CT and MRI 57

contrasts such as T1 weighted images, T2 weighted images, proton density images, inversion recovery images, fat saturated images and gradient recalled images.

MR imaging has several advantages over CT scan such as superior soft tissue contrast, direct multiplanar capability and excellent visualization of the optic nerve and intracranial pathology. Availability of higher field strength magnets and surface coils have significantly improved the image quality in orbital imaging. However, the long acquisition times that degrade the image quality due to movement artifacts and poor visualization of bony details and fractures still remain a significant impediment in the use of MRI for orbital evaluation. Furthermore, MRI is contraindicated in patients with cardiac pacemakers and defibrillators, neurostimulators, metallic foreign bodies in the eye, and other ferromagnetic implants within the body.

Though, the signal pattern is highly dependant upon the specific imaging parameters used during acquisition, in general the signal patterns of various orbital and other related structures can be described as follows:

Currently, the information obtained on imaging studies is complementary. The choice of imaging study should be based on the clinical presentation and the specific pathology being suspected. Further, the imaging techniques can be modified to specifically address the pathology in question. Discussion with the radiologist performing the imaging study goes a long way in ensuring optimal imaging of the orbit. While ordering for the imaging, the decision depends upon the nature of lesion. However I (MS), very rarely, if at all ask for a plain X-ray of orbit. The

58 Surgical Atlas of Orbital Diseases

information obtained from a plain X-ray is very limited and grossly inadequate to understand the nature of the lesion and plan management (Figure 3.1).

My most preferred imaging modality is CT scan of Orbit, 2 mm slices of axial, coronal sections with sagittal reconstruction, with or without contrast. Contrast studies are ordered only when vascular or tumor pathology is suspected clinically. Otherwise plain study alone is ordered. For example, in thyroid orbitopathy, plain study is asked for, contrast study is not indicated. My preference for CT is because of its easy availability, cost to the patient, easy interpretation. I ask for an MRI only when I am dealing with a lesion of optic nerve or its sheath which account for 2 to 3% of all cases of proptosis.

Evaluation of a CT scan of orbit: Though the soft tissue lesion attracts our attention, it is prudent to read the CT scan image in a systematic method, so that we don't miss any subtle changes, which provide very useful information.

The level of the scan: The orbital scans are normally taken in a sequential order, from below upwards for axial scans and from anterior to posteriorly in coronal scans. To know the level of

the scan in the axial sections, remember that the medial walls of the orbit are parallel in the midorbit (Figure 3.2). If they were not parallel, the level of the picture is either lower or upper. Look at anterior and posterior parts of the picture. Anteriorly a flat nasal root and posteriorly the presence of brain tissue indicate that the scan was of upper part of the orbit (Figure 3.3). A prominent nose anteriorly, and the presence of oropharynx posteriorly indicate that the picture was of lower part of orbit (Figure 3.4). The important structures of orbit at various levels are shown in Figures 3.5, 3.6 and 3.7.

Figure 3.2: Mid level: Note the medial

Figure 3.4: Note the prominent nose anteriorly (blue arrow) and the or opharynx posteriorly (yellow arrow). Normal anatomy of orbit on CT

Figure 3.6: Axial CT scan at mid level of orbit showing important structures

Figure 3.5: Axial CT scan at lower level of orbit showing important structures

Figure 3.7: Axial CT scan at upper level of orbit showing important structures

Common mistakes: We wish to discuss some of the common mistakes committed by the residents while interpreting the CT scan of the orbits. They are described with Figures 3.8 to 3.10.

How to read?

•Anatomical location /level

•Bony orbit

•Eye ball

•Extra ocular muscles

•Optic nerve

•Soft tissue Lesions

—Borders / consistency

•Hounsfield units

•Contrast enhancement

Figure 3.10: Enlarged Optic canal is how most of the residents interpreted A which is in fact enlarged inferior orbital fissure. Compare its size with normal inferior orbital fissure (B) Remember that optic canal is seen at the level of anterior clinoid processes and you will be able to see superior orbital fissure lateral to optic canal (Figure 3.6).

Figure 3.12: Bony erosion and hypertrophy in a case of fungal granuloma of orbit. Look at the “irregular” borders of the bone in comparison to the smooth borders of the excavation (Figure 3.11) Bony erosion is due to infiltration of the bone. It is commonly seen in malignant lesions or fungal infections

Figure 3.14: Fungal granuloma of the maxillary sinus with bony erosion (yellow arrows) Leading to extension into the ethmoid sinus, orbit and cheek

Figure 3.15: Bony dehiscence: Dumbbell Dermoid involving maxillary sinus and orbit. Note the absence of floor (yellow arrow). Note also the smooth excavation of the maxillary sinus and its expansion