Evaluation of Orbital diseases by Computed Tomographic Examination
Sudhir Bhagotra, Ashok K Sharma, Yogesh Puri

ABSTRACT

Purpose: To study the presentation patterns of orbital diseases primarily affecting the orbit and its contents and to assess the ability of CT in defining the characteristics of orbital diseases.

Methods: Fifty patients with orbital diseases formed the subject matter of the present study. Detailed history and clinical examination was conducted.  Computed tomographic examination was carried out with 3rd generation Siemen Somatom- DR CT scanner. The orbit was scanned in axial and coronal planes, plain axial scans were obtained.  These were followed by CECT by injecting iodine contrast injection I/V in some cases.  The CT scan findings were correlated with surgical and histopathological findings to recall at final diagnosis.

Results: The mass lesion, site of origin and their extent was better delineated on CT than by plain radiography.  Retinoblastoma was the commonest childhood malignant disease and calcification was hallmark of retinoblastoma.  Adult patients had paranasal sinus malignancy and orbit was involved after eroding the bony walls.

Conclusions: Computed tomography is of utmost importance in evaluating the orbital diseases especially when performed in orthogonal planes.  It is also of great importance in the diagnosis and defining fields of surgery and radiotherapy.

Keywords: Computed tomography, Retinoblastoma, Orbital diseases.

INTRODUCTION
Before introduction of CT in orbital imaging, plain radiographic examination was used to evaluate clinical problems of pain, proptosis, diplopia or diminution of vision.  Plain radiography was helpful in assessing injuries but was disappointing for study of masses, inflammatory conditions of the orbit and soft tissues.

CT has become imaging modality for evaluating trauma, tumors, endocrinal and inflammatory lesion.  Contrast enhancement may add definition and specificity in setting of orbital tumours, vascular malformations and inflammations.  Interior of the globe is easily inspected by direct visualization.  The strength of CT includes exquistic bony detail, speed of examinations and excellent spatial resolutions.  Orbital fat provides excellent inherent contrast allowing easy separation of tissues in orbit. Rapid post processing of CT image provides 3D picture of lesions and helps surgeons in salvaging the normal structures during surgery.  It is also possible to obtain appropriate tissue for biopsy under CT guidance and place the radioisotope in malignant tissues where other treatment modalities are not effective.

MATERIAL AND METHODS
Fifty patients with orbital diseases formed the subject matter of present study.  Patients were referred to Department of Radiodiagnosis and Imaging after detailed history and clinical examination.

CT examination was carried out with 3rd generation Siemen Somatom-DR CT scanner.  CT sections included axial and coronal scans.  Axial scans were of 4 mm thickness parallel to the inferior orbitomeatal line. The coronal scans were also of 4 mm thickness and were done in a plane perpendicular to axial plane.  The patients were placed in prone position with head hyperextended in coronal scans.  The posterior extent of coronal scans was anterior clinoid process.  It was extended to dorsum sellae in appropriate cases.

Optic nerve lesions were studied with 2 mm sections to improve the CT characteristics of the lesions.  Lesions were normally evaluated using appropriate soft tissue window depth.  Where there was suspicion of bone destruction, bone window widths were used for detailed evaluation of the orbital lesions.  Both NECT (Non contrast) and CECT (Contrast enhanced) scans were obtained in the present study.

Table 1

Evaluation of orbital diseases on the computed tomographic examinations of 50 patients

S.No. Disease Process No. of Cases %age
1. Retinoblastoma 9 18
2. Pre-septal cellulitis 6 12
3. Frontal and ethmoidal sinus mucocele 6 12
4. Maxillary sinus carcinoma 4 8
5. Nasopharyngeal carcinoma 4 8
6. Pseudotumour 3 6
7. Post septal cellulitis 2 4
8. Cavernous haemangioma 1 2
9. Orbital lymphoma 1 2
10. A-V malformation with inflammatory extra ocular muscle enlargement 1 2
11. Cysticercosis of the eye 1 2
12. Lacrimal gland carcinoma 1 2
13. Ethmoidal cell carcinoma 1 2
14. Rhabdomyosarcoma 2 4
15. Bony outgrowth at medial canthus 1 2
16. Normal 7 14

RESULTS
About 50% of the patients had malignant lesions, Normal scans were observed in seven patients although they had clinical signs and symptoms (Table-1). The study covered patients over wide range of age from 3 years to 80 years. 40% of the patients were in the age group or 21-40 years, 30% or the patients were less than 20 years of age and 30% of the patients were more than 40 years of age.  Ratio of male to female was 3:2. In our study patients presented with varied eye symptoms (Table-2) Most of the patients had more than one symptoms related to the diseased eye.  complete loss of vision was seen in twelve cases while nine patients had reduced visual acuity.  Six patients had sudden loss of vision while the rest fifteen had progressive deterioration of vision. Associated findings observed were

(a) History of trauma in two patients of arterio-venous (AV) malformation

(b) Recurrent attacks of upper respiratory tract infections were observed in patients of mucocele and preseptal cellulitis.

(c) There was correlation of port meat intake and cysticercosis in eye.

The distribution of cases according to signs is tabulated' under Table 3.  Proptosis was the commonest sign seen.  None of our cases showed cranial nerve palsy.    

Table 2

Distribution of cases according to symptomatology

S.No. Symptoms in affected eye No. of Patients
1. Pain in the affected eye 36
2 Bulging of the eyeball 22
3. Loss of vision 21
4. Double vision 13
5. Swelling around the eye 12
6. Excessive lacrimation 9

Ten (20%) patients had duration of illness less than a week and 16 (32%) of the cases had duration of illnes more than one year.  Characteristics reported by the radiologist on CT evaluation of orbit are tabulated under Table 4.

Most or the Orbital diseases had more than one predominant CT characteristic on evaluation.  Strong contrast enhancement wwwas noticed in patients of cavernous hemangioma.  Mild to moderate contrast enhancement was seen in orbital lymphomas, retinoblastoma, lacrimal gland carcinoma and pseudotumour patients.

Involvement of fat planes was observed in 15 (30%) of the patients.  Conventional films did not define extraconal or intraconal fat planes where as CT scan demonstrated both intraconal and extraconal fat planes.  CT scan was found superior in demonstrating bony was erosion in 13 (26%) of the cases as compared to 5 (10%) by plain radiography, Orbital enlargement was demonstrated in 10 (20%) of the cases while plain radiographs revealed orbital enlargement in 5 (10%) of the cases only.  Plain radiography could not pick up intra orbital calcification in any of the cases while CT demonstrated intra orbital calcification in 9 (18%) of the cases, Calcification was seen in six cases of retinoblastoma and two cases of ethmoidal sinus mucocele.

Table 3

Distribution of cases according to signs

S.No. Clinical Signs on affected side No. of Patients
1. Proptosis 22
2 Loss of vision  
  (a) Total loss of vision
(b) Partial loss of vision		 12
9
3. Diplopia 13
4. Absent direct pupillary reflex 16
5. Painful movements of eyeball  
  -Full range
-Restricted		 6
13
6. Palpable swelling around eye  
  -Firm
-Soft		 8
4
7. While pupillary reflex 6

No case showed Cranial Nerve Palsy

Table 4

Comparison between plain radiography and computed tomography findings in evaluating the orbital diseases characteristics.

S.No. Characteristic Evaluated On plain
Radiography
No. of Patients		 On CT

No of Patients
1. Soft tissue mass   23
2. Calcification - 9
3. Orbital enlargement 5 10
4. Bone destruction & erosion 5 13
5. Eyeball involvement Not seen 18
6. Optic nerve involvement Not seen 7
7. Intracranial extension & extraorbital extension Not seen 3
8. Contrast enhancement - 32

Extra ocular muscle involvement was seen in seven patients.  these included four cases of pseudotumour and one case each of rhabdomyosarcoma, postseptal cellulitis and AV malformation. These findings could not be observed on plain radiography (Table-4).

In our study we noticed 23 (46%) cases of mass lesion.  In retinoblastoma with calcification the diagnosis was obvious on CT images.  In cavernous hemangioma and rhabdomyosarcoma because of risk of bleeding and implantation of maliginant cells respectively, fine needle aspiration cytology (FNAC) was not done.  FNAC was done in 13 cases and diagnostic clue was obtained in 7 cases. The orbital diseases were clinically suspected and CT made significant contribution in diagnosing the lesion and demonstrating their true extent.

DISCUSSION
Orbital diseases involve all the age groups and primarily affect the orbit and its contents.  Eye ball is surrounded by bony orbit rendering most of eye ball and retrobulbar structures inaccessible for clinical examinations.  CT is a useful investigation to study orbital diseases.

Mafee (1987) and Kubal (1997) reported that retinoblastoma is the most common intraocular malignancy of childhood and occurs unilateraly in 66-77% of the patients.  Most of the patients are less than three years of age.  They described retinoblastoma as mild to moderately hytperdense lesions with uniform contrast enhancement.  Calcification was hallmark of diagnosis.  It was noticed in 90% of the patients. Spread of the disease was manifested by thickening of the optic nerve and presence of retrobulbar mass.  In our study there were 9 patients of retinoblastoma.  Left eye was affected in 66.6% of cases.  There was no case of bilateral or trilateral diseases.  All the patients were below 5 years of age.  White pupillary reflex was noticed in six cases.  Seven patients showed calcification. Optic nerve was thickened in three patients. No patient showed extra orbital extension.

Wibur et al (1987) reported that carcinoma of the paranasal sinuses frequently involves the bony orbit and is associated with bone destruction.  Most of these were squamous cell carcinomas.  Involvement was either through the roof of the maxillary antrum or eroding the lamina papyracea.  Paranasal sinus carcinoma presented as homogeneous mass with moderate contrast enhancement.  Bony destruction was observed on CT.  In our study there were 5 cases of para nasal sinus carcinoma (10%).  All were squamous cell carcinomas.  Four patients (8%) had maxillary sinus carcinoma and one patient (2%) had ethmoidal cell carcinoma.  Zygoma and greater wing of sphenoid was involved in two patients (4%) of maxillary sinus carcinoma.  Ethmoidal cell carcinoma has intraorbital and intra cranial extension through lamina papyracae and frontal bones respectively.

Willbur et al and Peyster et al, (1987) reported that nasopharyngeal carcinoma involved orbit directly or indirectly through inferior orbital tissue.  It presented as soft tissue mass with bone destruction.  In our study there were four patients of nasopharyngeal carcinoma (8%).  All of them presented as soft tissue mass with bone destruction.  These showed mild contrast enhancement on CECT. There was infra temporal extension on the same side in 3 cases.

Towbin et.al (1986) divided orbital cellulitis into preseptal and postseptal cellulitis.  The dividing line was periosteum forming the orbital septum anteriorly.  Preseptal cellulitis involved lid, conjunctiva and lacrimal sac.  It presented as medical canthal mass as described by Russel et.al (1985) and Friedman et.al (1993).  It was asociated with infection of the adjoining paranasal sinuses especially ethmoidal sinuses.  Weber et al  (1987) and Hershey and Roth (1997) found postseptal cellulitis as subperiosteal accumulation of pus which involved the extraconal space.  The medial rectus muscle was enlarged and enhanced on contrast administration.  In our study we had 6 patients (12%) of preseptal cellulitis.  There was involvement of adjacent ethmoidal air cells in 3 patients (6%).  Two patients of preseptal cellulitis had medial rectus muscle enlargement and fluid collection beneath the periosteum.  It was in conformity with the findings of Towbin et al.  There was no paranasal sinus involvement.  The patients presented with proptosis and diplopia on inward gaze.  It had firm swelling at medial canthus.  These findings were in agreement with Friedman et al (1993).

Mucoceles are the result of chronic blockage of the draining ostia of the sinuses.  There are alirless mucoid filled and expanded paranasal sinuses. They present as para orbital masses. Mucoceles are common in ethmoidal and frontal sinuses.  The slow expansion by the mucocele causes thinning of the surrounding bone.  The glboe is pushed forwards and laterally. These impair the motion of extra ocular muscles.  These are difficult to diagnose on conventional films.  On CT, these appear as homogeneous density expansile masses.  These had smooth margins and well defined erosions as reported by Wilbur et al (1987) and Weber et al (1987). In our study we had 6 (12%) cases of mucoceles.  Ethmoid sinus was involved in all the cases.  Two patients (4%) had associated frontal sinus involvement.  On CT homogeneous density mass filling the ethmoid sinus was observed.  There was bulging of lamina papyracae into the orbit.  These findings co-related well with findings described by Weber et. al (1987).

Nugent et.al. (1981) and Curtin (1987) reported that all their patients of pseudotumour had unilateral involvement and they responded very well to steroids.  In our study there were 3 (6%) cases of pseudotumour who had acute symptoms.  Two patients had medial rectus muscle involvement with obliteration of extra conal fat (myositis).  These findings were similar to that of Nugent and Curtin.   

Mafee et al (1997) reported cavernous haemangioma as hyupodense lesion on CT scans with obliteration of the fat planes.  In our study there was 1 (2%) case of cavernous haemangioma.  It presented as hypodense lesion in the retrobulbar area.  The mass lesion pushed the globe outwards and upwards.  The fat planes of the orbit were obscured.  Straightening of the optic nerve was observed.  The lesion showed strong contrast enhancement and enlargement of the bony orbit.  These findings co-related well with Mafee et al (1987).

We evaluated 1 (2%) patient of lacrimal gland carcinoma.  The mass was of mixed density.  It occupied both extra and intraconal fat planes pushing the eyeball forwards, downwards and medially.  Malignant nature was illustrated by destruction of the greater wing of sphenoid and zyogma.  On CT, no calcification was detected.  Mass extended into infra temporal fossa on the same side.  These findings were in conformity with the studies conducted by Jackobiec et al in (1982), Maret and Haik ((1987) and Sharma et al (1981).

One case of orbital lymphoma was seen as mixed density tumour with enhancement on contrast administration.  The globe was pushed downward and medially with no globe deformation. Orbit was enlarged but there was no bone erosion.  No systemic evidence of lymphoma was seen in our patients.  These findings were similar to that of Yeo et al (19820 and Flanders et al (1987).

Rhabdomyosarcoma is the commonest cause of proptosis in small children. We had two patient of rhabdomyosarcoma in our study.  There was short history of proptosis and strabismus.  Conventional films were normal. On CT there was a mass along medial wall of the orbit which extended back, to the orbital apex with no intra-cranial extension. It was isodense and there was no bone involvement.  Patient improved after chemotherapy and radiotherapy treatment.

We observed one case of cysticercosis in the lateral wall of the orbit.  It showed cystic structure of 3-4 mm in size.  The cyst had pin head area of increased attenuation.  These findings were in conformity with the reports of Vashist et al (1991).  Only unusual thing noticed in our study was the site of ocular cysticercosis.

We had one patient of AV malformation.  This patient presented with proptosis, partial loss of vision and pain in the eye.  There was history of trauma to the affected eye.  Conventional films were unequivocal. On CECT, dilatation of superior ophthalmic vein was observed which enhanced strongly.  The extraocular muscles were enlarged and cavernous sinus was normal.

In the present study we had normal CT scan in seven patients.  These were suffering from sudden loss of vision (6) with mild proptosis and conventional radiographs were normal.  This further stressed the role of computed tomography that it not only detected the organic cause of symptoms but also helped in ruling out the mass lesion as cause of symptoms.

CONCLUSIONS
Computed tomography is of utmost importance in evaluating the orbital diseases especially when performed in orthogonal planes.  It is also of great importance in defining the field of surgery and radiotherapy.

Computed tomography is strongly recommended for follow-up of the patients of orbital disease for evaluation of recurrence of disease after surgery or radiotherapy.

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Address for Correspondence
Dr. Sudhir Bhagotra, Deptt. of Ophthalmology, Medical College, Jammu.