Iris Arteriovenous Malformation
Iris arteriovenous malformations (AVM) are rare benign vascular lesions which have also been called iris racemose hemangiomas. This is not a true neoplasm, but rather an anomalous arteriovenous malformation with a tangle of vascular channels at the site of the communication.
These vascular lesions are congenital. They are not associated with any systemic or ocular conditions.
The basic underlying pathology is an artery connects directly to a vein bypassing the capillary network. This is thought to be due to a local failure of mesenchymal cell maturation. In normal early vascular development, primitive mesenchymal cells differentiate into solid cords, which then become canalize to form capillary networks. As blood enters the system, arteries, capillaries, and veins are formed. The intervening capillaries then retract and atrophy. In iris AVM, extensive atrophy occurs, leaving a single channel to shunt blood across the defective capillary zone.
On microscopic examination, iris AVMs appear as telangiectatic vessels lined by endothelial cells.
The diagnosis of Iris AVM can be made on a clinical basis with careful slit lamp examination. While these lesions are benign in nature, they must be differentiated from other causes of abnormal iris vessels such as other iris hemangiomas, pathologic neovascularization of the iris, and dilated normal vessels resulting from chronic inflammation. Additionally, these lesions often present with a sclera sentinel vessel and thus concomitant malignancy such as uveal melanoma must be ruled out.
These lesions are non-progressive. While they are congenital in nature, most cases of iris AVMs are reported to present during the sixth decade.
Careful slit lamp exam reveals a tortuous, dilated vascular loop running from iris root to peripupillary region and back. These lesions usually are two clock hours in size. Additionally, these vessels can be visualized by gonioscopy.
Iris AVMs are typically asymptomatic and do not impair visual acuity.
Iris Fluoroscein Angiography (FA) can be used in diagnosis. FA will reveal a rapidly filling hyperfluorescent lesion with no late phase leakage. Intervening iris hypoperfusion can be visualized as well. In patients with darker irises, iris indocyanine green angiography can be used to for better penetration through the pigmentation and minimal leakage may be seen.
While generating a differential diagnosis, the clinician should consider iris hemangioma in addition to causes of abnormal iris vasculature, such as pathologic neovascularization of the iris, dilated normal vessels resulting from chronic inflammation, and dilated normal vessels resulting from underlying malignancy.
The other iris hemangiomas include capillary hemangioma, cavernous hemangioma, microhemangioma, and iris varix. Capillary hemangiomas typically present in infancy and can be associated with the systemic conditions of diffuse neonatal hemangiomatosis (DNH) and periorbital capillary hemangioma. These lesions appear as multiple iris hemangiomas and on microscopic examination appear as closely packed, flattened endothelial cells separated by a connective tissue stroma. Cavernous hemangiomas also typically present in infancy or childhood and appear as multilobulated blood-filled lesions that mimic clusters. The can also be associated with DNH as well as CNS and cutaneous hemangiomas. On microscopic examination, they appear as large, cavernous vascular spaces with intervening connective tissue stroma. Microhemangiomas appear in adults as tiny vascular tufts usually found near the pupillary margin and can be associated with diabetes mellitus and myotonic dystrophy. On microscopic examination, they appear as small, tightly coiled blood vessels. Iris varices also appear in adults as well circumscribed, multiloculated blood filled cysts. They do not have any systemic associations but are prone to thrombosis and hyphema. On microscopic examination, they appear as dilated vascular channels and often have a central thrombus.
Since iris AVMs are benign, non-progressive lesions, the treatment of choice is observation with periodic follow-up.
While complications of iris AVM are rare, the most common complication arising is spontaneous hyphema. Iris AVM associated hyphema is managed as primary hyphema. Additionally, depending on the location of the iris AVM, any intraocular surgery, such as cataract surgery, should prompt careful attention by the surgeon.
Iris AVMs carry very little risk for morbidity or mortality and thus confer an excellent prognosis.
- BSCS Section 2. Fundaments and Principles of Ophthalmology
- BSCS Section 4. Ophthalmic Pathology and Intraocular Tumor
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