Persistent Hyperplastic Primary Vitreous

A 1 y o baby with Left side Leukocoria clinically. Advised MRI orbit, with referring letter mentioning PHPV Vs Retinoblastoma by Ophthalmologist. 

MRI Brain T1w image show left side micro ophthalmos, hyper intense vitreous with a linear low signal intensity structure running antero posteriorly from lens to optic disc. 

Non contrast CT sections for orbit of same patient show no obvious evidence of dystrophic calcification rules out Retinoblastoma. Vitreous is hyper dense may be due to an associated retinal detachment. 

Impression: left side PHPV

Persistent Hyperplastic Primary Vitreous

Also known as persistent fetal vasculature, a rare congenital developmental malformation of the eye, due to a failure of normal regression of the embryonic hyaloid vascular system.
In the normal situation the primary vitreous forms around 7 th week of gestation life and starts involuting around 20 th week and nearly always disappears at the time of birth.
Persistent fetal vasculature in PHPV can lead to fibrosis, resulting in elongation of the ciliary processes, retinal detachment, and spontaneous cataracts.

Clinical presentation is usually unilateral or bilateral leucocoria, may also have poor vision, small eye (microphthalmia) and strabismus. PHPV is the second most common cause of leukocoria. (Retinoblastoma is most common cause of leukocoria in childhood) These patients also develop glaucoma and cataract.
It may be bilateral as a part of congenital syndromes such as Norrie disease.

What is Leukocoria ?
Normally when a light shines through the iris, the retina appears red to the observer.
In leukocoria (white pupil) the retina abnormally appears white.

Sub types of PHPV are Anterior (Ventral) or Posterior (Dorsal) types with most patients with PHPV having a combination of these.
Associations of PHPV are it can occur on its own or in association with various other conditions like Norrie disease,Warburg syndrome, retinal dysplasia particularly when bilateral.

Imaging findings:
A persistent canal may be seen that goes from the optic nerve to the lens. Retinal detachment occurs in 30-55%.
Ocular ultrasound: An echogenic band may be seen in the posterior segment of the globe extending from posterior surface of the lens to the optic nerve head. On colour Doppler, arterial blood flow was may be seen within this band.
On CT Orbit, appearance can be quite variable and the described spectrum of CT findings includes soft-tissue replacement (infiltration) of the vitreous body, retrolental soft tissue along the Cloquet canal - fine linear structure extending from the head of the optic nerve to the posterior surface of the lens, absence of abnormal calcification within the orbit, microphthalmus, retro hyaloid layered blood, hypervascularity of the vitreous humor on post contrast, Recent onset Retinal detachments may be hyperdense on CT.
On MRI, the MRI findings of the anterior type of PHPV included a shallow or collapsed anterior chamber, an anterior segment anomaly, and a retrolental vascular membrane which demonstrated hyperintensity after contrast enhancement. MRI findings of the posterior type consisted of microphthalmos; a tubular image, representing the hyaloid vessel; a funnel-shaped retinal detachment, with the subretinal fluid hyperintense on both T1- and T2-weighted images; the fluid-fluid level, which was hypointense on both T1- and T2-weighted images and probably corresponded to the presence of hemorrhage in the subretinal space; a retrolental mass; and vitreous hemorrhage.

Differential diagnosis 
Clinically closely mimics a retinoblastoma.
On Ultrasound the main differential is retinal detachment.
MRI is the investigation of choice.

Imaging wise PHPV Vs Retinoblastoma
PHPV as associated with Micro ophthalmia and optic nerve atrophy where as in Retinoblastoma there may be Macro ophthalmia with Optic nerve enlargement due to tumor extension. Dystrophic calcification is not a feature of PHPV where as its common in Retinoblastoma.