Ординатура / Офтальмология / Английские материалы / Oculoplasty and Reconstructive Surgery Made Easy_Garg,Touky, Nasralla_2009
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Imaging of the Orbit 279
NEUROGENIC LESIONS OF THE ORBIT
Optic Nerve Sheath Meningioma
Introduction: Optic nerve meningiomas are slow growing tumors. They may be extradural, subdural, or combined.
Signs and symptoms: The primary symptom is the diminished visual function. In early stages, it may be subtle such as defective color vision, enlargement of the blind spot, and transient obscuration of vision. The advanced disease, the visual acuity is diminished, and there is constriction of the visual fields.
The patient may have mild proptosis. The fundus examination may show choroidal folds, optic nerve head edema and opticociliary shunt vessels.
Computed tomography: The optic nerve on CT scan is enlarged, in a tubular or globular fashion. There may be a central lowdensity linear ‘tram-track’ appearance, which denotes the optic nerve. There may be a nodular appearance where the tumor breaks through the dura into the orbital tissues. It may sometimes grow eccentrically and produce amass on one side of the optic nerve. Some tumors may show flecks of highdensity calcification, or adjacent hyperostosis. About 6% may be bilateral (Figure 22A).
MRI Imaging: On T1 weighted images, the meningioma is a tubular or fusiform lesion, iso-intense or hypointense to the optic nerve. Fat suppressed T1 images better demonstrate the tumor and its extension into the orbital soft tissue, distinct from the optic nerve. On T2 weighted images, the tumor is isointense or hyper-intense to the orbital fat (Figure 22B).
T1 weighted sequences after contrast injection show the enhancement of the tumor, and are the best for detecting intracanalicular or intracranial extension of the tumor.
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Figures 22A and B: (A) Axial CT scan of bilateral optic nerve sheath meningioma, showing thickening of optic nerve, with few flecks of calcification. (B) Axial view of the same in a T2-weighted MRI sequence, showing hyper-intense thickening of the optic nerve sheath bilaterally, with central hypo-intense shadow of the optic nerve
Investigation: Imaging of the brain is required to rule out other intracranial meningiomata, which are found in 5% of bilateral meningiomas.
Differential diagnosis: Optic nerve meningioma should be differentiated from optic nerve glioma on imaging, because both may cause fusiform enlargement of the optic nerve. However, the optic nerve glioma has a smooth outline, while the meningioma has a nodular appearance due to the extradural extension. Further, optic nerve glioma may show a buckling or kinking, which a meningioma will not.
Treatment: An isolated anterior meningioma may be resected. A meningioma causing progressive visual loss may be treated with external beam radiotherapy. An eye with no visual prognosis, with severe proptosis is occasionally exenterated along with resection of the intracranial tumor.
Optic Nerve Glioma
Optic nerve gliomas are low-grade astrocytomas that present early in life. They may be confined to the orbit, or have chiasmal and extrachiasmal involvement.
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Signs and symptoms: The patient may present with visual loss, progressive proptosis and strabismus. On examination, the child may have optic disc edema, optic atrophy, or constricted visual fields.
Approximately 30% of patients with optic nerve glioma may have features of neurofibromatosis type 1.
CT scan imaging: CT scan appearance of an optic nerve glioma is generally characteristic, with fusiform swelling, which has smooth outlines. The optic nerve may be kinked. The lesion may have a few low density areas of cystic degeneration
(Figure 23A).
MRI scan: On MRI, the enlargement of the optic nerve shows a fusiform appearance, with iso-intense to nervous tissue. The lesion may have a hypo-intense surrounding arachnoid hyperplasia. The T2 weighted image is hyper-intense, occasionally heterogeneous, and has peripheral hypo-intense arachnoid hyperplasia. The tumor shows enhancement on contrast injection. Contrast enhancement also helps to identify the extension of the glioma intra-cranially (Figure 23B).
Figures 23A and B: (A) Axial CT scan of bilateral optic nerve glioma shows fusiform swellings of the optic nerve, and proptosis. (B) Sagittal view, T2-weighted MR imaging of optic nerve glioma. The Optic nerve shows fusiform enlargements, which are hyperintense, with a small hypointense area, and kinking of the optic nerve
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Investigation: A biopsy may be required to distinguish an optic nerve glioma from a meningioma, in which case it should be remembered that the surrounding arachnoid hyperplasia may give a confounding histopathologic diagnosis.
Treatment: If there is a visual deterioration, the condition may be treated with chemotherapy or radiotherapy. A rapidly growing tumor may need tumor resection, with a tumor-free proximal end of the optic nerve.
Extraocular Extension of Intraocular Tumor
Signs and symptoms: The patient presents with proptosis and diminished vision. Retinoblastoma is a common cause of orbital extension of intraocular tumor. The child in an advanced stage of retinoblastoma would present with leucocoria, as well as proptosis and limitation of extraocular movement. The condition may be painful, and inflammatory signs such as lid edema may be present.
Computed tomography: The intraocular tumor is visible within the globe. In a retinoblastoma, the CT scan will show an intraocular tumor with high density areas of calcification. There may be a discontinuity in the sclera, and the tumor is seen to extend into the orbital tissues as a homogenous irregular mass lesion. A thickened optic nerve denotes optic nerve extension of the tumor (Figure 24).
Figure 24: Axial view of CT scan in orbital extension of retinoblastoma. The globe is filled with a soft tissue density shadow of the tumor, with a few high density spots of calcification. The posterior contour of the globe is disrupted, and the tumor extends into the orbit
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Investigations: the clinical features and imaging are characteristic. In doubtful cases incision biopsy may be performed.
Bone marrow biopsy, CSF cytology and CT scan brain are performed to rule out remote spread of tumor.
Treatment: The prognosis is poor. High dose chemotherapy along with enucleation and external beam radiotherapy can reduce the mortality.
Optic Neuritis
Signs and symptoms: Optic neuritis presents with diminution of vision; the color vision and contrast sensitivity are affected earlier than the visual acuity. There may be recurrent episodes, other cranial nerve palsies associated.
Magnetic resonance imaging: The MRI shows an abnormality in 54 to 85% of the patients with optic neuritis. The optic nerve may show Demyelination in the intraorbital, intracanalicular or intracranial segment. Lesions may be missed if they are smaller than the section thickness. On the T1 sequence, the affected segment of the nerve is iso-intense to normal nerve tissue; it becomes hyper-intense in the fat suppressed GdDTPA enhanced sequences, or on T2weighted images
(Figure 25).
Figure 25: T1-weighted, fatsuppressed sagittal view after Gd-
DTPA injection showing enhancement of a segment of intraorbital optic nerve in optic neuritis
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Investigation: MRI of the brain may demonstrate other demyelinating plaques.
Management: The management may be conservative, intravenous steroids or administration of interferon. The reader is advised to consult specific texts for guidelines.
BIBLIOGRAPHY
1.Byrne SF, Green RL. Ultrasound of the Eye and Orbit. Mosby-Year Book, St Louis, 1992.
2.Cockerham KP, Kennerdell JS. In Smith’s Ophthalmic Plastic and Reconstructive Surgery, 2nd edition. Mosby-Year Book, St Louis, 1998.
3.De Potter P. Advances in imaging in oculoplastics. Curr Opin Ophthalmol 2001;12:342-6.
4.De Potter P, Flanders AE, Shields CL, Shields JA. Magnetic resonance imaging of orbital tumors. Int Ophthalmol Clin 1993;33(3):163-73.
5.Lemke AJ, Kazi I, Felix R. Magnetic resonance imaging of orbital tumors. Eur Radiol 2006;16:2207-19.
6.Naik MN, Tourani LT, Chandra Sekhar G, Honavar SG. Interpretation of computed tomography imaging of the eye and orbit. A systematic approach. Ind J Ophthalmol 2002;50:339-53.
7.Rootman J. Diseases of the Orbit. A Multidisciplinary Approach. 2nd edition. Lippincott Williams and Wilkins, Philadelphia, 2003.
INTRODUCTION
Until the computed tomography (CT) was introduced the orbit was considered the “black box” in ophthalmology. The magnetic resonance imaging (MRI) has even put the spotlight on the orbit, which has made it possible to early diagnosing neoplasms of the orbit promising theoretically a better prognosis. That has not been fulfilled as the neoplasms are often seen in an elderly population that will seek help late. The neoplasms have also often a slow growth bringing the patient late to his ophthalmologist, due to symptoms from the visual organs as proptosis, diplopia, ophthalmoplegia, ptosis, anisocoria and pain. Changes in vision due to neuropathy or astigmatism from pressure on the bulb or compression of the bulb inducing choroidal folds are often symptoms coming later.
A completely history especially covering earlier cancers as breast cancer in women and prostate cancer in men, thyroid disorders, autoimmune disease, infectious diseases and medical treatment with immune suppressive treatments.
A complete neuro-ophthalmologic evaluation of the patient with problems from the orbit is mandatory. Exophthalmos is easily measured by a Hertel exophthalmo-
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meter; protrusion more than 21 mm and a difference of more than 2 mm between the two eyes is pathologic. The displacement of the eye can give a suspicion where to look for the tumor in the orbit.
A palpation of the orbit will tell if the resistance is soft or hard if any pain is felt which might differ infection/ inflammation from a solid neoplasm.
The ophthalmologist is often the first physician but the evaluation and treatment is multidisciplinary involving otorhinolaryngologist, radiologist, oncologist, plastic surgeon and oromaxillofacial surgeon. If metastases to the orbit is suspected further specialists are involved in the search for diagnosis and treatment.
It is not the purpose of this chapter to give a fully description of all neoplasms seen in the orbit, but rather to give a short presentation of the most common types seen by the author and even a very rare type will be presented, the Merkel cell carcinoma.
The adult orbital neoplasms differ from the neoplasms seen in childhood. Most neoplasms are seen late in life and many invade from the paranasal sinus. The neoplasms can primarily arise from the tissue in the orbit itself or secondary from the paranasal sinus and by invasion from neoplasms of the paraorbital skin (eyelids) and metastatic.
Lymphoid tumors are the most common neoplasm of the orbit seen in 10 to 13%. In a population over the age of 60 the incidence accounts for 24% of orbital neoplasms. Many patients have or will developed systemic lymphoma of nonHodgkin type. The most common seen malignancy in the paranasal sinus is squamous cell carcinoma. Squamous cell carcinoma is seen in 9% of tumors of the eyelids and 10% of carcinomas involving the orbit, but represent one of the most
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seen skin cancers. In two-thirds of the patients orbital invasion is seen, pointing to a poor prognosis. Adenocarcinomas and adenoid carcinomas make up 5% all of tumors involving the orbit and are highly invasive.
Half of the lacrimal glad tumors are epithelial neoplasms, the other half are malignant lymphoma, benign lymphoid hyperplasia and leukaemia. Inflammatory lesions and lymphoid neoplasms of the lacrimal gland are assessing to be seen 2 to 3 times more common than the epithelial neoplasms.
Orbital meningiomas and schwannomas are most often seen in the fourth to seventh decade of life. 70% of the meningiomas invade the orbit from the cranium. This type of tumor has often a very slow growth, so in the old patient an excision of the tumor might never be needed. The prognosis for good visual acuity after an operation is very poor as the tumor often growth along the optic nerve.
A schwannomas is a benign neoplasm arising from a nerve in the orbit. Seen between 20 to 70 years of age. The therapy is surgical removal of the tumor.
A relatively common vascular lesion of the orbit is the cavernous hemangioma. Most often seen in adults with peak incidence around 40 years of age. It shows a slowly, painless growth over several years with a progressing proptosis. The treatment is surgical excision.
The metastatic tumors represent approximately 8% of all orbital tumors (Figures 1 and 2). Breast carcinoma followed by lung metastasis in women. In the men the most common metastatic tumors are lung and prostate. The mean age is seventy years of age.
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Figures 1 and 2: Recurrence adenocarcinoma
PRIMARY TUMORS OF THE ORBIT
Orbital Lymphoma of the Orbit
Introduction
The most common primary tumor of the orbit is the orbital lymphoma, 10% of the tumors of the orbit, and 40-60% of the lymphoproliferative diseases of the orbit. The lymphomas are often unilateral most often starting in the lacrimal gland.
The new diagnostic positron emission tomography (PET) and gastrointestinal endoscopy will often unveil a systemic non-Hodgkin’s lymphoma (NHL) with a secondary spread to the orbit. The majority is NHL and is mainly seen after 50 to 70 years of age (Figures 3A and B).