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Background
The lateral ventricles are paired C-shaped cerebrospinal fluid (CSF)-filled structures that are the largest component of the ventricular system. Each lateral ventricle has 5 main anatomic components, including the body, trigone and the frontal, occipital and temporal horns with a capacity to store 7-10 mL of CSF.

Educational Goals / Teaching Points
Discuss normal anatomy and embryological development and review anatomic variations and frequently encountered congenital lesions including cavum septum pellucidum and vergae, cavum vellum interpositum, ventricular coaptation, xanthogramulomas and connatal cysts. Review lesions involving the lateral ventricles including but not limited to choroid plexus papilloma and carcinoma, central neurocytoma, subependymoma, meningioma, metastasis and subependymal spread of high-grade gliomas and lymphoma.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Anatomic variants, congenital lesions (cavum septum pellucidum - slit-like CSF filled space between two leaflets of the septum pellucidum, cavum vergae reflects posterior extension beyond the columns of the fornix). Cyst of the velum interpositum (large cystic structure with bulging walls at the posterior aspect of the lateral ventricles following CSF signal). Neoplasms (central neurocytoma - WHO grade II tumors, typically attached to the septum pellucidum. CT demonstrates a hyperattenuating mass, frequently with calcifications. MRI demonstrates slightly T2/FLAIR hyperintense lesion with cystic areas and heterogeneous enhancement, choroid plexus carcinoma - WHO Grade III tumors arising de novo from choroid plexus epithelium in the trigone of the lateral ventricles). CT demonstrates a heterogenous, slightly hyperattenuating mass, frequently with calcifications. MRI demonstrates a lesion iso to hypointense on T1/T2 with intense heterogeneous enhancement. Necrotic/cystic can be seen. Hydrocephalus is common. Miscellaneous lesions (choroid plexus cysts - benign entity following CSF signal on all sequences). Choroid plexus xanthogranuloma (common incidental finding, seen in the trigone of the lateral ventricles and frequently bilateral. Variable T1/T2 signal characteristics dependent on lipid content). Demonstrate restricted diffusion on diffusion weighted imaging (DWI).

Conclusion
Several anatomic variants and incidental lesions are frequently encountered that should not be mistaken for pathology, including cavum septum pellucidum and vergae, cavum vellum interpositum and ventricular coaptation and xanthogramulomas. Connatal cysts may be seen incidentally adjacent to the frontal horns of the lateral ventricles and should be differentiated from periventricular leukomalacia or sequalae of germinal matrix hemorrhage. Congenital malformations, including dysgenesis of the corpus callosum and schizencephaly may result in characteristic abnormalities of ventricular morphology. Neoplasms can occur in characteristic locations within the lateral ventricles, including choroid plexus papilloma and carcinoma, central neurocytoma, subependymoma, meningioma, metastasis and subependymal spread of high grade gliomas and lymphoma. We review and present cases of these entities.