P14.06: Difficult differential diagnosis of an occipital mass

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A 30-years old primigravida was referred at 24 weeks for the evaluation of an occipital mass. Ultrasound revealed an extracranial mass of approximately 27 × 20 mm, with a wide implantation base, fine trabeculations in its interior, an echogenic core and no vascular signals at power Doppler. No underlying bony defect was apparent, nor any intracranial abnormality. Prenatal MRI excluded bony defects and meningocele. The couple were informed that the most likely diagnosis was that of a lymphangioma. However, they were explained that alternative diagnoses were possible. The mass was followed up with ultrasound, shrinking in size to 7 × 20 mm at 31 weeks. After delivery, a repeat MRI scan suggested the presence of a fluid-filled meningocele with a very thin neck at level of the lambda. There was an associated venous vascular variant, with the falcine sinus converging towards the superior sagittal sinus. The mass was excised. Histopathological examination showed, in the hypodermis, a tissue characterized by a conspicuous vascularisation, composed of cells embedded in a myxoid matrix. the cells were predominatly spindled in shape, with oval nuclei displaying a vesicular chromatin; cytoplasms were faintly eosinophilic. Some multinucleated cells were seen. The vessels had the morphological features of dilated venules. The epidermis overlying the lesion was atrophic. The lesion was surrounded by scalp skin, rich in follicular structures. The immunohistochemistry demonstrated both in spindle and multinucleated cells expression of vimentin and smooth muscle actin. There were no cells positive for EMA, GFPA or synaptophysin. A final diagnosis of benign tumor of mesenchimal origin was formulated. The risk of local recurrence is expected to be low.

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