Choroid plexus xanthogranuloma

Xanthogranulomas of the choroid plexus are common, incidental and almost invariably asymptomatic lesions. It is unclear in much of the literature whether they represent a distinct entity from adult choroid plexus cysts, but they share imaging characteristics and are only likely to be distinguishable on autopsy ⁵. As the clinical history is the same, the distinction, at least from a radiologist's and clinician's point of view, is largely irrelevant. 

For the purpose of this article the term xanthogranuloma is used as it is easier to distinguish from choroid cysts, often thought of in the context of antenatal screening. 

Epidemiology

Adult choroid cysts and xanthogranulomas should not be confused with antenatal choroid cysts, which usually regress by birth. These lesions are found in adults, and are relatively common (~7%) ^2,5, identified most commonly in older patients ⁵. 

Clinical presentation

In almost all cases these lesions are asymptomatic. Rarely they are large enough to cause local mass effect or may be complicated by haemorrhage ⁶. 

Pathology

These lesions represent desquamated epithelium into the lumen of choroid cysts within the choroid plexus. As a result cholesterol / lipid rich content of epithelial cells accumulates, sometimes combined with blood products, and results in a xanthomatous response, as this material is ingested by mononuclear cells ^1-2,5. 

Histologically these lesions are characterised by xanthomatous debris filling needlelike spaces representing the apparent site of lipid crystals admixed with blood pigments, multinucleate histiocytes, and focal collections of foamy histiocytes. 

Radiographic features

The size of xanthogranulomas of the choroid plexus varies widely, ranging from tiny spec-like regions, not visible on imaging, to large prominent choroidal masses. In most cases they measure below 1 cm in diameter and are usually located in the trigones of the lateral ventricles ⁵. They are bilateral in two thirds of cases ⁵. 

CT

On CT these lesions are usually inapparent as they are of similar density of the adjacent choroid plexus. When larger they can be inferred by the displacement of choroidal calcifications around their periphery. 

MRI

Signal characteristics on MRI are variable depending on the mixture of lipid, fluid and blood products. In general they mimic cystic lesions, although they do not fully attenuate on FLAIR. A helpful feature is that they usually have quite high signal on diffusion weighted imaging (DWI). This high signal is seen as a result of both true restricted diffusion and T2 shine through (as expected the ADC signal is intermediate rather than particularly low) ⁵. 

Treatment and prognosis

These lesions require no treatment. They do not require histological confirmation and no follow up is needed. 

Differential diagnosis

On CT the main differential is that of a cysts of the choroid plexus.

On MRI, the diagnosis is usually readily made, with the two potential differential being:

1. acute infarction of the choroid plexus ³
   • both can have high signal on DWI 
   • infarcts are unilateral whereas xanthogranulomas are usually bilateral
2. choroid cyst ^4-5
   • depending on the definition, this can be the same thing
   • cysts can follow CSF on all sequences, but often have altered signal due to protein and blood products