Ординатура / Офтальмология / Английские материалы / Oculoplasty and Reconstructive Surgery Made Easy_Garg,Touky, Nasralla_2009
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Congenital Tumors 249
Figure 2: An infant with capillary hemangioma
Prognosis
These tumor grow for 3-6 months after birth and slowly regresses by second year of life. Spontaneous resolution occurs in 40% by 4 years of age and 80% by 8 years.
Management
Surgery is indicated in cases of total ptosis obscuring the visual axis and induced astigmatism and for better cosmesis.
Intralesional injection of 1-2 ml of corticosteroid. Betamethasone 6 mg/ml and triamcinolone 40 mg/cc combined in 1:1 concentration and is injected all around the lesion with 26 G needle deep into the lesion (Figure 3). Rapid shrinkage occurs in first two weeks and then continues slowly for several months. Injection may be repeated after 6 weeks in case of residual mass. Depigmentation of overlying skin, eyelid necrosis and rarely central retinal artery occlusion are few complications seen with steroid injection.
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Figure 3: Injecting corticosteroid in the hemangioma
Dermoid and Epidermoid Cyst
Abnormal sequestration of surface ectoderm beneath the skin during embryonic development results in the cyst formation (Figure 4). Lids are usually secondarily involved due to extension of the tumor from the orbits.
Figure 4: Showing swelling superonasally of dermoid
Congenital Tumors 251
Signs
They are clinically evident by first year of life. Most common location is superonasal. On palpation, these are firm in consistency, nontender and are attached to underlying periosteum.
Investigation
Imaging is necessary to know the extension.
Management
Surgical excision is required in case of progressive enlargement of mass.
Plexiform Neurofibroma
Involvement of the lid with plexiform neuroma in cases of neurofibromatosis (Figure 5). Café au lait spots are characteristic of neurofibromatosis.
Figure 5: Showing plexiform neurofibroma of let upper lid
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Management
Surgery is indicated in cases of significant mechanical ptosis and to improve cosmesis. Surgical debulking of the mass along with ptosis correction and lateral shortening may be performed.
Prognosis
These tumors cannot be fully excised and recurrence is common.
To conclude, pediatric abnormalities poses challenges for an ophthalmologist. Patient’s cooperation is a limitation for adequate assessment in paedatric age group. Cosmetic consideration is also critical for child’s psychological development. It is important to carefully assess and plan the technique of intervention for gratifying results.
INTRODUCTION
The commonly used orbital imaging modalities are computed tomography (CT scan), ultrasonography and magnetic resonance imaging (MRI). The most useful and most commonly used is the CT scan, although the other modalities are very useful in some specific situations. For the systematic approach to interpretation of orbital computed tomography imaging, the reader is recommended to consult the references quoted. In this chapter, we shall discuss orbital imaging of selected orbital pathology with respect to computed tomography, and specific features best identified with MRI scanning or orbital ultrasound. All imaging has to be interpreted in context of the clinical presentation.
COMPARISON OF THE THREE MODALITIES
Computed Tomography
A thin collimated fan-shaped beam of X-rays emanate from the machine, pass through the tissue and are detected and converted into signals. Areas of greater density are depicted as brighter on the image, while lower density areas are depicted to be darker. CT scan of the orbit, at 2 mm slices shows orbital processes with high anatomical accuracy. Bones
Imaging of the Orbit 255
of the orbit are imaged well. A lesion which becomes brighter after intravenous injection of contrast material is said to be enhancing. Contrast-enhancement is seen in vascular and cystic lesions.
Magnetic Resonance Imaging
The part of interest is placed in a strong magnetic field, and the protons in the tissue rotate to align their magnetic fields to that of the superimposed field. When the field is switched of, the protons regain their previous orientation, emitting energy in the process. The emitted energy is detected and converted to signals. Any tissue that contains a higher number of free protons will emit a stronger signal, whereas cortical bone, which is nearly devoid of protons, shows up black in an MRI. Depending on the relaxation times and weightage given, the T1 weighted images show fat to be brighter, or hyper-intense, and water to be darker, or hypo-intense. The T2 image shows orbital fat as dark, and water, including vitreous humor and cerebrospinal fluid to be brighter, or hyper-intense. Lesions may enhance with the contrast agent Gd-DTPA, best seen on fat-suppressed T1-weighted images.
The MRI scan is able to image orbital soft tissues and their relationship in detail, but has poor histologic specificity. Most tumors are hypo-intense on T1-weighted images and hyperintense on T2 weighted images. Vascular lesions enhance well on contrast injection. Lack of enhancement may be seen in cystic lesions or less vascular areas such as scar tissue. MRI scans can help in the differential diagnosis of hemorrhagic lesions, and can detail the optic nerve and orbital apex lesions.
Orbital Ultrasound
Sound waves with frequency in the ultrasonic range are transmitted through the tissues. The reflected waves are
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detected and converted into images, two-dimensional in case of the B-scan and linear in case of the A-scan. Highly reflective tissues are represented as being brighter.
Echography may be used as an adjunctive imaging modality, in lesions that involve the globe and adjacent orbit. It can detect cystic lesions of the orbit well.
EVALUATION OF CT SCAN ORBIT
The maximum information is elicited from an orbital imaging by evaluating it systematically:
The bony orbit: The orbital roof, floor, medial and lateral walls, orbital apex, optic foramen, inferior orbital fissure.
•Eyeball
•Extaocular muscles: size, shape, laterality and distribution of muscle enlargement, muscle margins, contrast enhancement.
•Extraconal tissues.
Intraconal tissues: Optic nerve, superior ophthalmic vein
• Sella and parasellar regions.
Any orbital space-occupying lesion is to be assessed in termsofitssize,location,shape,circumscription,effectonsurrounding soft tissue, effect on surrounding bone, internal consistency, contrast enhancement and extraorbital invasion.
THE ORBITAL BONES
The orbital bones are best imaged by a CT scan; MRI and Ultrasonography have little role to play. In this section we shall be discussing the bony lesions of the orbit. Changes in the bones secondary to disease processes will be mentioned with the relevant disease process.
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Osteoma
Introduction: An osteoma is a tumor-like mass of bony tissue; in the vicinity of the orbit, they arise most commonly form the frontal sinus, followed by ethmoid, maxillary and sphenoid sinuses. The mass extends into the orbit and causes proptosis and globe displacement.
Computed tomography: The CT scan shows a well-defined, wellcircumscribed mass, arising from the sinus and invading the orbit. They may have a bosselated surface, and may be sessile or pedunculated. The bone window shows a very dense periphery, and lower density inside, due to the cancellous internal structure (Figures 1A and B).
Differential diagnosis: An osteoma is to be differentiated from other bony tumors like ossifying fibroma and fibrous dysplasia.
Investigations: A patient should be evaluated for multiple osteomas, retinal pigment epithelial hypertrophy and soft tissue tumors. These are associated with Gardner’s syndrome, which needs colonoscopy to rule out premalignant intestinal polyps.
Figures 1A and B: (A) Coronal view of right frontal osteoma, bone window setting. (B) Axial view of same, in soft tissue window setting. The bony lesion appears uniformly dense
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Treatment: If asymptomatic, osteomas may be treated conservatively. The tumor can be excised via orbitotomy.
Ossifying Fibroma
Signs and symptoms: Ossifying fibroma or fibro-osseous dysplasia involves a single bone; near the orbit, it affects the frontal, ethmoid or maxillary bones, and extends into the orbit. The lesion may cause asymptomatic proptosis.
Orbital imaging: There is a well-circumscribed mass, with a thin rim of high density sclerotic bone. The internal structure shows multi-loculated heterogeneous density due to the osteoblastic and osteolytic areas (Figures 2A and B).
Differential diagnosis: Histopathologically it is to be differentiated from fibrous dysplasia.
Investigation and management: The tumor tends to recur if removed incompletely. Total excision needs to be done; for a large tumor, combined orbital, neurosurgical and rhinological approaches are needed.
Figures 2A and B: (A) CT scan image, coronal section of the well-defined lesion, with heterogeneous internal density, involving the ethmoid and maxillary sinuses, the nasal cavity and the orbit. (B) Axial view of the lesion showing the lesion displacing the extraocular muscles and the optic nerve