Female, 27 years old, 27 weeks gestational age, with fetal brain lesion identified on ultrasound. A space occupying lesion is present centered on the right ambient cistern measuring 22 x 18 x 16 mm. The lesion displaces adjacent structures including the right thalamus, internal cerebral veins, right medial temporal lobe, and brainstem, without clearly arising from any of them. As such, the lesion could potentially be extra-axial. The margins of the lesion are well circumscribed without evidence of parenchymal infiltration or edema. Internally, the lesion is homogeneously T2 hyperintense and markedly T1 hyperintense, with a moderate degree of restricted diffusion. The margins of the lesion show susceptibility effect, with little if any susceptibility internally.Brain parenchymal morphology, and the degree of sulcal development, are appropriate for gestational age. The corpus callosum is present and within normal limits. The cavum septum pellucidum is present. The left ventricular atrium measures top normal in size at 10 mm, but the remainder of the ventricular system is within normal limits. The posterior fossa structures are unremarkable. The right globe is hypoplastic or absent with dysmorphic or rudimentary orbital structures.
A well circumscribed, space occupying lesion is present centered on the right ambient cistern. The lesion displaces adjacent structures without infiltration or parenchymal edema. The origin of the lesion is not clear, but it could potentially be extra-axial. Internally, the lesion is homogeneous and T2 hyperintense, but also markedly T1 hyperintense with rim susceptibility. This could indicate hemorrhagic products, fatty material, or viscous/proteinaceous material.The differential for this lesion remains broad, but overall, the characteristics are relatively non-aggressive, and as such, a benign etiology is favored. The lesion could represent pure hemorrhage, or a hemorrhagic cyst. Developmental cysts including epidermoid and dermoid should be considered as well. A neoplastic process is not excluded, though the imaging features on the present study are not typical of a teratoma, which would be the most common fetal tumor. Also noted is hypoplasia or absence of the right globe, with dysmorphic/rudimentary orbital structures. Please note that this interpretation is made without the benefit of comparison to ultrasound images. As soon as these images can be obtained, a comparison will be made, and if a change to the interpretation is warranted, an addendum to this report will be issued.