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IMAGING IN ORBIT

IMAGING IN ORBIT. IMAGING TECHNIQUES. X-RAY ULTRASONOGRPHY CT SCAN MRI MRA. X RAY. Not commonly used now a days because A three-dimensional structure is seen in two dimensional plane, giving rise to disturbing superimposition.

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IMAGING IN ORBIT

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  1. IMAGING IN ORBIT

  2. IMAGING TECHNIQUES • X-RAY • ULTRASONOGRPHY • CT SCAN • MRI • MRA

  3. X RAY • Not commonly used now a days because • A three-dimensional structure is seen in two dimensional plane, giving rise to disturbing superimposition. • Moreover, its sensitivity to small differences in the attenuation is low • , i.e., its contrast resolution is poor.

  4. X-RAY • WATERS VIEW • CALDWELL’S VIEW • LATERAL VIEW • SUBMENTOVERTEX VIEW • RHESE VIEW

  5. WATERS VIEW: Waters projection is created by placing the chin of the patient on the x-ray cassette with the canthomeatal line (the line that connects the lateral canthus and the external auditory meatus) at 37 degrees to 45 degrees

  6. (a, frontal sinus; b, medial orbital wall; c, innominate line; d, inferior orbital rim; e, orbital floor; f, maxillary antrum; g)superior orbital fissure; h, zygomatic-frontal suture; i, zygomatic arch)

  7. CALDWELL’S VIEW: The patient is positioned with both the nose and forehead against the x-ray cassette while the x-ray beam is directed downward 15 degrees to 23 degrees to the canthomeatal line.

  8. (a, frontal sinus; b, innominate line; c, inferior orbital rim; d, posterior orbital floor; e, superior orbital fissure; f, greater wing of sphenoid;g, ethmoid sinus; h, medial orbital wall; i, petrous ridge; j, zygomatic-frontal suture; k, foramen rotundum) 

  9. LATERAL VIEW: lateral projection (Fig. 4) is created by placing the patient's head against the x-ray cassette and centering the cassette on the lateral canthus. The x-ray beam is directed perpendicularly to the midpoint of the cassette and enters the patient's head at the lateral canthus remote from the cassette

  10. Radiograph of a lateral projection. (a, orbital roof; b, frontal sinus; c, ethmoid sinus; d, anterior clinoid process; e, sella turcica; f, planum sphenoidale)

  11. SUBMENTOVERTEX VIEW :this projection is obtained with the patient's neck extended either in the supine or upright position. The top of the head is placed so that the infraorbitomeatal line is parallel with the x-ray cassette. The x-ray beam is directed at right angles to the infraorbitomeatal line

  12. (a, zygomatic arch; b, orbit; c, lateral orbital wall; d, posterior wall of maxillary sinus; e, pterygoid plate; f, sphenoid sinus

  13. RHESE VIEW: The zygoma, nose, and chin should touch the cassette. The x-ray beam is directed posterior-anteriorly at 40 degrees to the midsagittal plane

  14. Radiograph of an oblique apical projection. (a, right optic canal; b, optic strut; c, superior orbital fissure; d, ethmoid sinus; e, planum sphenoidale; f, greater wing of sphenoid) 

  15. X-RAY SIGNS OF ORBITAL DISEASES • SIZE OF ORBIT • CHANGE IN BONE DENSITY • CHANGE IN ORBITAL SHAPE • DEHISCENCE OF ORBITAL BONES • INTRAORBITAL CALCIFICATION • ENLARGEMENT OF SUP. ORBITAL FISSURE • CHANGE IN OPTIC CANAL

  16. SIZE OF THE ORBIT • SYMMETRICAL ENLARGMENTobserved in intraconal lesions e.g ; optic nerve glioma, hemangioma ASYMETRICAL ENLARGEMENTobserved in extraconal lesions e.g; rhabdomyosarcoma, dermoid cyst

  17. CHANGE IN BONE DENSITY • Localised decreased density/indentation of the orbital wall.Benign tumors like, dermoid, mixed cell lacrimal gland tumor • Diffuse bony destructionmalignant tumors like, lacrimal gland carcinoma

  18. SUP.WALL DESTRUCTION IN RHABDOMYOSARCOMA

  19. CHANGE IN ORBITAL SHAPE • As a result of local expansion of the orbital wall Orbital dermoids Encapsulated lacrimal gland tumors

  20. Intraorbital calcification • Retinoblastoma • Orbital varix • Optic nerve sheath meningioma • Phthisical eye

  21. Enlargement of Sup.Orbital fissure • Infraclinod carotid aneurysm • Extraseller extension of pitutary tumors

  22. Changes in Optic Canal • Normal dimensions: Vertical 6mm Horizontal 5mm • Abnormal when , Asymmetry greater than 1mm, Vertical dimension greater than 6.5mm

  23. Optic canal enlargement • Seen in, • Regular enlargement • Optic nerve glioma • Aneurysm of ophthalmic artery • Irregular enlargement • Retinoblastoma • Optic nerve sheath meningioma

  24. OPTIC CANAL ENLARGEMENTIN OPTIC NERVE GLIOMA

  25. Optic canal compression • Seen in • Fibrous dysplasia • Paget’s disease • Hyperostosis secondary to meningioma • Microphthalmos

  26. OPTIC CANAL COMPRESSION IN FIBROUS DYSPLASIA

  27. X-RAY IN ORBITAL WALL/RIM FRACTRURES • TRIPOD FRACTURE • BLOW OUT FRACTURE

  28. TRIPOD FRACTURE

  29. ORBITAL FLOOR FRACTURE

  30. Intraorbital foreign body

  31. Intra ocular foreign body

  32. CT SCAN OF ORBIT • ADVANTAGE: • BONY DETAILS /CALCIFICATION • SPACE OCCUPYING LESION CAN BE VISUALISED IN THREE DIMENSIONS BY COBINATION OF CCT AND CAT • STRUCTURES LIKE GLOBE ,EOM, OPTIC NERVE CAN BE VISUALISED • IN ORBITAL TRAUMA FOR DETECTING SMALL ORBITAL WALL # IOFB HERNIATION OF EOM

  33. DISADVANTAGE • INABILITY TO DISTINGUISH BETWEEN PATHOLOGICAL SOFT TISSUE MASS WHICH ARE RADIOLOGICALLY ISODENSE • RADIATION INDUCED CATARACT

  34. CT scan is most informative, • when the ophthalmologist seeks active participation of the radiologist in the diagnostic work-up. • The clinical information supplied by the referring ophthalmologist is used by the radiologist .

  35. Major consideration while requesting a CT Scan • Slice thickness • Imaging plane • Tissue window • Contrast enhancement • Modification of CT procedure • Orbit with brain CT

  36. Slice thickness • Spatial resolution of a CT depends on slice thickness. • The thinner the slice, the higher the resolution. • Usually, 2mm cuts are optimal for the eye and orbit. • In special situations (like evaluation of the orbital apex), thinner slices of 1mm can be more informative.

  37. Imaging plane • Routine CT scan involves axial& coronal views . • Saggital view: along the axis of the inferior rectus muscle is important in evaluation of orbital floor blow-out fractures.

  38. A spiral CT is Preferable when reformatted sagittal cuts are required. • The plane inclined at 30° to the orbito-meatal line  best depicts the optic canal and the entire anterior visual pathway.

  39. Tissue window • Each tissue window has a specific window width and window level. • Soft-tissue window  is best for evaluating orbital soft tissue lesions, • Fractures and bony details are better seen with bone window settings .

  40. Contrast enhancement • Evaluation of optic chiasma, perisellar region and extra-orbital extensions of orbital tumours. • Helps to define vascular and cystic lesions as well as optic nerve lesions, particularly meningioma and glioma.

  41. Modification of CT procedure • Certain cases may require special modifications during the scanning procedure to aid diagnosis. • In a case of orbital venous varix, it is important to request for special scans (with contrast) while the patient performs a Valsalva maneuver.

  42. Simultaneous brain CT • Suspected neurocysticercosis with orbital involvement. • Head injury with orbital trauma • Optic nerve meningiomas

  43. Components of CT scan • Patient dataThis includes the name, age, gender of the patient as well as the date of the CT scan . • Type of CT scan • Plain CT scan • Contrast enhancement • It will be printed next to each image whether the scan is plain or contrast enhanced.

  44. Laterality • The best way to confirm laterality is to look for the "R" or "L" mark which represents right or left respectively .

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