Conventional Radiography Conventional radiography of the orbit can be performed with a survey radiograph of the paranasal sinuses in an occipitomental view (paranasal sinus radiograph OM), which is the so-called “Waters projection.” A lateral picture can be performed additionally. The optic nerve canal can be visualized by a “Rhese projection,” but, to date, this is of minor importance. 1 Because of minor thickness of the bony orbital walls, especially of the orbital floor ( ▶ Fig. 4.1), discontinuities of bony structures are difficult to visualize by conventional radiographic techniques. This is why conventional radiographs are becoming less used in trauma cases. Their use is limited particularly to postoperative position control following reposition of bony fragments and osteosynthesis ( ▶ Fig. 4.2), or in localization of foreign bodies in the orbit ( ▶ Fig. 4.3). Small glass splinters from clear glass are not visible in a radiograph; with a wavelength of 10 picometers to 1 nanometer, the electromagnetic radiation is not absorbed or reflected by glass. Fig. 4.1 Orbital floor fracture on the left side. Discontinuity of the left bony orbital floor (arrow). Fig. 4.2 Position control following repositioning and miniplate osteosynthesis. Correct position of the lateral orbital wall and orbital floor. Fig. 4.3 Surgical instrument (needle) in the periorbita. Lateral projections can be useful in radiopaque foreign body localization (arrow). With modern multislice or spiral CT scanners, volume data sets can be captured, from which sections in any planes and in any thickness can be computed. Usually axial, coronal, and sagittal pictures with a thickness of 2 mm are produced. Because of the high radiosensitivity of the eye lens, modern low-dose examination protocols are used for the orbit to achieve maximal picture quality with minimal radiation exposure. For bony orbital structures, orbital pathways, and intraorbital muscles, refer to ▶ 1 ( ▶ Fig. 4.4, ▶ Fig. 4.5). Fig. 4.4 Radiological anatomy of the orbit. (a, b) Axial CT scans in bone window. (c, d) Axial CT scans in soft tissue window. (a) 1, ethmoid; 2, lamina papyracea (orbital lamina); 3, zygomatic bone; 4, sphenozygomatic suture; 5, greater wing of the sphenoid bone; 6, inferior orbital fissure; 7, sphenoid sinus. (b) 1, superior orbital fissure; 2, optic canal; 3, anterior clinoid process. (c) 1, lacrimal gland; 2, medial rectus muscle; 3, lateral rectus muscle; 4, optic nerve; 5, internal carotid artery. (d) 1, tendon of superior oblique muscle; 2, lacrimal gland; 3, superior rectus muscle. Fig. 4.5 Radiological anatomy of the orbit. (a, b, c) Coronal CT scans in bone window. (d) Coronal contrast-enhanced CT scan in soft tissue window. (a) 1, fossa of lacrimal sac; 2, nasolacrimal duct; 3, infraorbital canal; 4, maxillary sinus. (b) 1, superior orbital fissure; 2, inferior orbital fissure; 3, sphenoid sinus; 4, pterygopalatine fossa. (c) 1, lesser wing of sphenoid bone; 2, superior orbital fissure; 3, optic canal; 4, foramen rotundum; 5, pterygoid canal. (d) 1, superior rectus muscle; 2, superior oblique muscle; 3, lateral rectus muscle; 4, optic nerve; 5, medial rectus muscle; 6, inferior rectus muscle. For evaluation of an acute orbital trauma CT scans are crucial and are regarded as imaging technique of first choice. With the ability to visualize both bony and soft tissue structures, they enable rapid and accurate diagnosis of bony and soft tissue injuries (e.g., eyeball hematoma [ ▶ Fig. 4.6], eyeball rupture [ ▶ Fig. 4.7], retrobulbar hematoma, peribulbar hematoma, incarceration of outer eye muscles, prolapse of orbital adipose tissue, orbital emphysema). Fig. 4.6 Eye bulb perforation with hematoma. (a) Noncontrast axial CT scan shows an eyeball perforation along with an intraocular foreign body (glass splinter) and intraocular hematoma (arrow). (b) Axial CT scan in bony window allows differentiation between air that has penetrated into the orbit and the more dense fat. Fig. 4.7 Eyeball rupture. Noncontrast axial CT scan (a) and coronal CT scan (b) visualize the unrounded shape of the eyeball along with extensive periorbital hematoma. The short examination time for upset of the data set is of great advantage in evaluation of this frequently restless and agitated cohort of patients who have to be handled. Three-dimensional imaging is possible with 3D reconstruction, which is crucial when contemplating surgical procedures. Orbital fractures are fractures of the bony orbital walls that can extend to the orbital apex, with consequent incarceration of muscles, adipose tissue, or nerves. They can occur in isolation or in combination with midface or skull base fractures. Hence, they can affect either only a part of the orbit or the entire orbit, 2 which can lead to a prolapse of orbital content through the fracture line into the maxillary sinus (see ▶ 8) 3 ( ▶ Fig. 4.8, ▶ Fig. 4.9). Fig. 4.8 Orbital floor fracture (blow-out fracture). (a) Coronal CT scan in bone window shows the fracture of the orbital floor with dislocation of orbital adipose tissue and a larger bony fragment of the orbital floor (arrow) into the maxillary sinus. (b) Noncontrast coronal CT scan in soft tissue window displays a displacement of the inferior rectus muscle (arrow) through the fracture line along with its incarceration. Hematoma in the maxillary sinus. (c) Noncontrast axial CT scan additionally shows a retrobulbar hematoma (arrow). Fig. 4.9 Fracture of the zygomatic bone (so-called “tripod-fracture”). (a) Axial CT scan shows a zygomatic arch fracture (arrow), and fracture of the lateral (arrow) and anterior bony walls of the maxillary sinus (arrow). Soft tissue emphysema (arrowheads). (b) Axial plane through the orbit, showing a dislocation of the bony lateral wall fragments (arrow), and a periorbital emphysema. (c) Coronal plane to demonstrate a dislocation of orbital floor fragments. The infra-orbital canal is also involved (black arrow). The frontozygomatic suture is burst (white arrow). (d) 3D reconstruction: fractures of the inferior and lateral orbital wall along with the zygomatic arch (arrows). Le Fort III fractures (centrolateral midface fractures) ( ▶ Fig. 4.10) are characterized by splintering of the entire midface skeleton including the bony nose from the skull base. The fracture line runs through the lateral orbital wall, orbital floor, medial orbital wall, and nasofrontal suture to the opposite side and through the zygomatic arches. Fig. 4.10 Le Fort III fracture. (a) Axial CT scan shows a fracture line coursing through the lateral orbital wall and orbital lamina on both sides, and involving the nose and nasal septum. (b, c) Coronal CT scans show the fracture line crossing the root of the nose and the orbital floor bilaterally. (d) 3D-reconstruction of the CT in the same patient. CT scans provide crucial information regarding the course of the optic nerve and probable injuries in patients in whom the nerve’s function cannot be clinically evaluated ( ▶ Fig. 4.11). Fig. 4.11 Injury of the optic nerve. (a) Axial CT scan in bone window showing a right-sided fracture of the minor and major wings of the sphenoid bone. (b) Compression of the optic nerve canal due to a bony fragment (arrow). (c) Coronal CT scan elucidates both the fracture and the obstruction of the optic nerve canal (arrow). (d) Noncontrast soft tissue coronal CT scan demonstrates the unaffected optic nerve on the left side (arrow) and the nerve compression on the right side (arrow). Magnet resonance imaging (MRI), which will be discussed in detail later, is generally superior to CT in the evaluation of orbital tumors. However, in cases of orbital tumors infiltrating the periosteum and/or adjacent bony orbital structures, CT scans can provide significant diagnostic information. Frequent tumorous lesions involving the bony orbital walls and wings of the sphenoid bones are osteomas ( ▶ Fig. 4.12), malignant tumors ( ▶ Fig. 4.13), fibrous dysplasia ( ▶ Fig. 4.14), and especially sphenoid wing meningioma. 4 Fig. 4.12 Frontal sinus osteoma. Coronal (a) and axial (b) CT scans show a right frontal sinus osteoma extending into the orbit. Note characteristic areas of different density inside the tumor, and the downward displacement of the eyeball. Fig. 4.13 Ewing sarcoma. (a) Contrast coronal CT in soft tissue window demonstrates a huge mass in the skull base area, extending intracranially and into the periorbita. (b) Coronal CT scan in bone window shows bilateral osteolytic destruction of the anterior skull base and the medial orbital walls. Fig. 4.14 Fibrous dysplasia. Axial (a) and coronal (b, c) CT scans show an extensive ground-glass appearance of altered bone. The optic nerve canal (arrows) is bilaterally surrounded and compressed by the mass. Osteoma (<1 per cent of all orbital tumors) frequently originates in the bones of the paranasal sinuses, whereas primary osteoma of the bony orbital walls is less frequent. Surgical resection is required only in cases with clinical symptoms. 4 Fibrous dysplasia is a benign developmental disorder of the bone affecting most frequently the orbital roof. It grows slowly, but the optic nerve canal is commonly involved. In case of clinical complaints, such as deterioration of visual acuity, decompression of the optic nerve is indicated. Dermoid cysts ( ▶ Fig. 4.15) are the most frequent cystic lesions in the orbit. They represent congenital lesions that manifest in childhood and early adolescence. 4 Dermoids contain fat and occasionally calcifications. Inflammation or rupture of these lesions can occur. Fig. 4.15 Dermoid of the left orbit. (a) Contrast coronal CT in soft tissue window shows a superior laterally located lesion with sharp margins, centrally hypodense with peripheral ring-shaped contrast enhancement. (b) Coronal CT scan in bone window shows erosion of the adjacent bone (arrow), which is a sign of a longer-lasting lesion. During this century the diagnostic use of CT scans has increasingly been replaced by MRI scanning, especially for diagnostic clarification of retrobulbar pathologies. Because of MRI’s better soft tissue contrast, both the visualization and the anatomical localization of orbital lesions is significantly more precisely than with CT. Taking account of the different signal intensities using different sequences some narrowing of differential diagnosis is possible with MRI. The lack of radiation exposure is another advantage of this technique. The topographical resolution can be significantly improved by using special orbit coils but excellent image quality and topographical resolution can also be achieved with the head coil of the newest MRI machines. For high image quality, it is crucial to avoid eye movements by the patient so as not to produce movement artifacts. Due to the relatively small orbital volume and small pathological structures, thin image slices of about 2.5 to 3.0 mm are required. Basically T1W and T2W sequences are captured. It is advantageous to perform T1W sequences with fat suppression following application of contrast agents, to suppress the significantly bright fat signal and allow visualization of small lesions that take up contrast agents. The bony cortical substance displays hypointensity (dark) in all sequences. The eyeball appears hypointense in T1W sequences and hyperintense in T2W sequences due to the fluid inside the organ. MRI is suitable for visualizing details of orbital anatomy. For demarcation of the topography of different orbital structures, scanning should be performed in axial, coronal, and sagittal planes ( ▶ Fig. 4.16, ▶ Fig. 4.17). Fig. 4.16 (a–d) Axial nonenhanced T1W MR images without fat suppression. (e, f) Coronal nonenhanced T1W MR images without fat suppression. (a) 1, orbital septum; 2, medial rectus muscle; 3, lateral rectus muscle; 4, optic nerve. (b) 1, lens; 2, posterior ciliary artery; 3, ophthalmic artery; 4, optic nerve; 5, cavernous sinus; 6, internal carotid artery. (c) 1, ophthalmic artery; 2, optic nerve; 3, anterior clinoid process; 4, hypophysis. (d) 1, trochlea; 2, lacrimal gland; 3, superior ophthalmic vein; 4, superior rectus muscle. (e) 1, lacrimal gland-orbital part; 2, aponeurosis of levator palpebrae superior; 3, lacrimal gland- palpebral part; 4, inferior oblique muscle; 5, inferior rectus muscle. (f) 1, superior oblique muscle; 2, levator palpebrae superior muscle; 3, superior rectus muscle; 4, medial rectus muscle; 5, lateral rectus muscle; 6, optic nerve; 7, inferior rectus muscle. Fig. 4.17 (a–c) Coronal T2W images with fat suppression. (d) Sagittal nonenhanced T1W image without fat suppression. (a) 1, optic nerve; 2, optic sheath. (b) 1, optic nerve; 2, anterior clinoid process; 3, cavernous sinus; 4, sphenoid sinus. (c) 1, anterior cerebral artery; 2, optic chiasm; 3, suprasellar cistern; 4, hypophysis; 5, internal carotid artery. (d) 1, orbital septum; 2, levator palpebrae superior muscle; 3, superior rectus muscle; 4, optic nerve; 5, inferior rectus muscle; 6, inferior oblique muscle. There is a wide spectrum of inflammatory diseases affecting the orbit, including infectious diseases, idiopathic orbital inflammatory disease (pseudotumors), optic nerve neuritis, and dysthyroid endocrine orbitopathy (Graves’s disease). Together they represent more than 50% of all orbital lesions. 5 Most acute orbital infections originate in the paranasal sinuses. However, orbital infections can also develop from infections of the face and pharynx, and can also be caused by a trauma or a foreign body. A proportion of them develop secondarily following septicemia. 6 Orbital cellulitis can be classified in five stages of orbital involvement 7: Inflammatory edema. Subperiosteal phlegmon and subperiosteal abscess. Orbital cellulitis. Orbital abscess. Ophthalmic vein and cavernous sinus thrombosis ( ▶ Fig. 4.18). Fig. 4.18 Orbital phlegmon and superior ophthalmic vein thrombosis. (a) Contrast-enhanced T1W image with fat suppression demonstrating diffuse contrast enhancement in the intraconal space. Enhancement is visible also in the walls of the thrombosed superior ophthalmic vein (arrow), whereas the vein’s lumen is spared. (b) The thrombosed superior ophthalmic vein can be recognized as a roundish structure (arrow) superolateral to the optic nerve in the coronal T1W image. (c) In contrast to the right side, the retrobulbar adipose tissue on the left side shows a hyperintense signal due to inflammatory infiltration and edema in the coronal T2W images with fat suppression. Note the swollen mucosa and obliteration of the maxillary sinuses on both sides and of the ethmoid cells. Graves’s orbitopathy ( ▶ Fig. 4.19) is an autoimmune disease and the most frequent cause of bilateral exophthalmos (see Chapter ▶ 7). The disease is characterized by a thickening of extraocular muscles, commonly the muscle bellies, and sparing of the muscles’ tendons. Muscle thickening is caused by an infiltration of lymphocytes, plasma cells, and mast cells and by deposition of hydrophilic mucopolysaccharides, with the inferior rectus muscle being most frequently affected, followed by the medial, superior, and lateral rectus muscles. Other clinical signs are thickening of the lacrimal gland, proliferation of orbital adipose tissue, and stretching of the optic nerve. Myositis is the most important differential diagnosis. Fig. 4.19 Graves’s orbitopathy. (a) Axial, T1W postcontrast fat-suppressed image shows a significant thickening and contrast enhancement of the muscle bellies of any extraocular muscle. (b) Coronal fat-suppressed T2W image shows hyperintense signal of the affected muscles, (c) Coronal postcontrast fat-suppressed T1W image shows that considerable muscle thickening leads to a compression of the optic nerve in the orbital apex (arrow). Idiopathic orbital inflammatory disease (IOID) ( ▶ Fig. 4.20) represents a heterogeneous group of unspecific inflammations of the orbital tissues for which no specific, systemic or local causes can be determined. 8, 9 The disease was first described by Birch-Hirschfeld as orbital pseudotumor. 10 Histopathologically a mixed infiltration by immature T lymphocytes, granulocytes, plasma cells, histiocytes, and macrophages occurs, accompanied by fibrosis. 11 The course of the disease can be acute, subacute, or chronic. Fig. 4.20 Anterior orbital inflammation with posterior scleritis. A 24-year-old woman with pain, slight proptosis, and lid swelling on the left side. (a) A hyperintensity in the retrobulbar adipose tissue adjacent to the sclera is shown by an axial fat-suppressed T2W image (white arrow). (b, c) Contrast administration leads to significant contrast enhancement of the posterior sclera and retrobulbar fat tissue in axial (b) and coronal (c) fat-suppressed T1W images (black arrow). Six sites of inflammation can be distinguished: anterior orbital inflammation, diffuse orbital inflammation, apical posterior orbital inflammation, lacrimal inflammation, orbital myositis, and perineuritis. The main clinical symptoms are pain, diplopia, and vision loss. A rapid improvement after application of glucocorticoids is typical in this disease. An acute inflammatory process of the optic nerve is termed optic nerve neuritis ( ▶ Fig. 4.21), which is most commonly due to multiple sclerosis (MS). 12 Optic nerve neuritis can also be caused by numerous diseases other than MS, e.g., autoimmune diseases (systemic lupus erythematosus), post- and parainfectiously during herpes infections, mononucleosis, rubella, toxoplasmosis, syphilis, borreliosis, or granulomatous diseases. Optic nerve neuritis is characterized by a hyperintense signal and swelling of the nerve in T2W images. Contrast enhancement of the nerve develops after application of a contrast agent ( ▶ Fig. 4.21a–c). Fig. 4.21 Left optic nerve neuritis in a patient with multiple sclerosis. (a) Coronal fat-suppressed T2W image shows swelling and hyperintense signal changes of the left optic nerve (white arrow). (b) Significant contrast enhancement of the left optic nerve after contrast administration in a coronal fat-suppressed T1W image (black arrow). (c) Contrast enhancement of the entire left optic nerve in axial fat-suppressed T1W images (white arrow).
4.3 Computed Tomography (CT)
4.3.1 Radiological Anatomy
4.3.2 Orbital Trauma
4.3.3 Tumors
4.4 Magnet Resonance Imaging (MRI)
4.4.1 Anatomy
4.4.2 Inflammatory Diseases
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