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Neuroradiology Case of the Week

Case 168

B. Keegan Markhardt, MD and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: A 69-year-old female with history of Marfan Syndrome with choronic vision loss.

Radiological Findings: Bilateral lenses lie in the dependent portion of the orbits (Figs. 1-5).

Diagnosis: Bilateral lens dislocation (bilateral ectopia lentis)

Discussion: The lens is considered dislocated or luxated when it lies completely outside the lens patellar fossa. The lens is described as subluxed when it is partially displaced, but contained within the lens space. Both conditions are described by the term “ectopia lentis.” The most common cause of ectopia lentis is trauma to the eye, which accounts for nearly one half of all cases of lens dislocation. Regardless of cause the mechanism involves dysfunction of the zonular fibers of the lens, and presents as marked visual disturbance. Generally, ectopia lentis may occur in any age group and has a male predominance.
     Marfan syndrome is the most frequent cause of heritable ectopia lentis. The syndrome is transmitted as an autosomal dominant trait with variable expressivity and has a prevalence of approximately 5 per 100,000. Several point mutations involving the fibrillin gene on chromosome 15 and 21 have been described and may relate to incompetent zonular fibers. Salient features of Marfan syndrome include tall stature, arachnodactyly, joint laxity, mitral valve prolapse, aortic dilatation, axial myopia, and increased incidence of retinal detachment. Lens dislocation occurs in about 75% of patients with Marfan syndrome and usually is bilateral, symmetrical, and supertemporal. Note that Ehlers-Danlos syndrome, often considered in differential diagnoses with Marfan syndrome, is only rarely associated with ectopia lentis.
     Homocystinuria is the second most common cause of hereditary ectopia lentis. It is an inborn error of metabolism most often caused by a near absence of cystathionine b-synthetase. Patients typically have fair skin with coarse hair, osteoporosis, mental retardation, seizure disorder, marfanoid habitus, and poor circulation. Lens luxation usually is bilateral, symmetrical, inferonasal, and present in nearly 90% of patients,
     Since both of these conditions may present with marfanoid habitus and bilateral lens luxation, it may be helpful to note that Marfan’s dislocation occurs supertemporal, while homocystinuria occurs inferonasal.
     A rare syndrome that may present with inferior lens subluxation is Weil-Marchensani Syndrome. These patients, however, typically are of short stature and have microspherophakia. Ectopia lentis may also occur as an isolated autosomal dominant inheritance genetic disease of chromosome 15. In this disease, the lens is displaced supertemporally and present at birth.
     Many primary ocular disorders are associated with unilateral ectopia lentis, including: congenital glaucoma, syphilis/chronic uveitis , retinitis pigmentosa, aniridia, hypermature cataract, high myopia, and intraocular tumor.

References:

1. Eifrig CW, Eifrig DE. Ectopia Lentis. Emedicine 2004. http://www.emedicine.com/oph/topic55.htm
2. Albert DM, Jakobiec FA. Pathology of the lens. In: Principles and Practice of Ophthalmology, 2000; 2225-2239.