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Editor,—Ocular metastases were previously thought to be rare.1 However, after having been extensively studied in patients with cancers, the incidence of ocular metastatic tumours increased.1-5 Haematological malignancy—including leukaemia, lymphoma, and multiple myeloma—is the most common primary cancer whereas mammary and pulmonary carcinomas are regarded as the most frequent intraocular metastatic carcinomas.1-5 We report an intraocular metastatic endodermal sinus (yolk sac) tumour which, to our knowledge, has not yet been described.
A 45 year old man presented with blurred vision in the left eye. Funduscopic study suggested a posterior choroidal tumour causing retinal detachment. Additional physical examination disclosed a 10 cm mass in the anterior wall of the chest.
Computed tomography of the thorax exhibited a mass, 13 × 11 × 8 cm, in the anterior mediastinum. The lesion with solid and cystic components extended into the right lung and anterior wall of the chest. Left enucleation was subsequently performed.
Grossly, the left eyeball revealed a grey white mass, 2 × 1.5 × 1.5 cm, with cystic degeneration in the posterior choroid. It protruded into the vitreous chamber (Fig 1). Microscopically, the ocular lesion was composed of glandular structures of various sizes lined by low columnar cells having large, oval, and basophilic nuclei with coarse granules of chromatin and inconspicuous nucleoli. Numerous eosinophilic hyaline globules were noted (Fig 2, upper). Schiller–Duval bodies, however, were not observed.
Immunohistochemical stainings revealed strong cytoplasmic positivity to α fetoprotein (Fig 2, lower), α-1-antitrypsin, epithelial membrane antigen, and cytokeratin. Stainings for S-100 protein, HMB-45, GFAP, NF, HCG, and CD30 were negative. The diagnosis was endodermal sinus tumour (EST). Subsequently, biopsy of the chest wall lesion consisting of a few pieces of grey tissue, 0.5– 1 cm in greatest dimension, was obtained. Sections revealed round vacuolated tumour cells forming nests and glands. Immunohistochemical study showed the same result as previously described in the ocular lesion. Furthermore, a high serum α fetoprotein level of 6850 IU/ml was detected. The final diagnosis was primary anterior mediastinal EST showing prominent glandular differentiation with metastasis to the left eyeball.
EST has several histological features such as reticular, polyvesicular-vitelline, hepatoid, endometrioid-like, intestinal, and mixed variants.6 Although Schiller–Duval body is the diagnostic hallmark of EST, it is not found in all cases.7 8 In our example, the diagnosis of EST was based on the morphology of the tumour cells, numerous hyaline globules, and identification of α fetoprotein in neoplastic cells as well as in serum. This pattern of EST with prominent glandular differentiation is similar to that originally described in the ovary by Cohen et al.7 A small sized ocular tumour compared with the mediastinal one as well as absence of any previous report on primary ocular EST makes us believe that the mediastinal EST is the primary cancer that metastasises to the left eyeball.
Malignant melanoma should be in differential diagnosis because it has diverse histopathological patterns and is common intraocular neoplasm in the West. However, hyaline globules are not the feature of malignant melanoma and there is no immunohistochemical finding to support. Moreover, the uveal melanoma is extremely rare in Thailand.9
In summary, we present an intraocular metastatic EST in which we suggest to spread from the anterior mediastinal EST. Although metastatic cancer to the eyes is currently believed to be the most common ocular malignancy,5 EST has not yet been recorded to metastasise intraocularly.
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