Persistent hyperplastic primary vitreous

Persistent hyperplastic primary vitreous (PHPV), more accurately known as persistent fetal vasculature (PFV), refers to an uncommon congenital developmental malformation of the eye.

Terminology

Because “primary vitreous” refers only to the hyaloid vessels that are posterior to the lens, the term “persistent fetal vasculature” was introduced in 1997 as a more accurate term because both the hyaloid vessels and the tunica vasculosa lentis persist in this condition ¹⁷.

Persistent fetal vasculature (PFV) is recognized by the International Classification of Diseases nomenclature.

Epidemiology

Associations

Persistent hyperplastic primary vitreous can occur in association with various other conditions, notably when bilateral. These include ⁹:

• Norrie disease

• Walker-Warburg syndrome

• retinal dysplasia

Clinical presentation

Clinically, this condition usually manifests as unilateral leukocoria, but can be bilateral ¹¹. Patients may also have poor vision, a small eye (microphthalmia) and strabismus.

Pathology

Persistent hyperplastic primary vitreous arises due to a failure of normal regression of the embryonic hyaloid vascular system (HVS). The hyaloid system, also called primary vitreous, is a transient vascular connective tissue which includes the hyaloid artery and vasa hyaloidea. It extends from the optic nerve to the posterior lens and helps nourish the developing fetal lens and avascular inner retina ^14,15.

Normally, the primary vitreous forms around the 7^th week of gestation, begins involuting around 20^th week and nearly always disappears by birth.

Persistent fetal vasculature in PHPV can lead to fibrosis, resulting in elongation of the ciliary processes, tractional retinal detachment, and spontaneous cataracts.

The underlying mechanisms behind the failure of these vessels to regress is not well understood.

Classification

PHPV can be divided into anterior (ventral) or posterior (dorsal) types, but it is often a combination of both ³.

Genetics

Persistent hyperplastic primary vitreous is sporadic in a majority of cases ¹⁵.

Radiographic features

From an imaging standpoint, only the features of posterior PHPV are well known ³.

Approximately 90% of persistent hyperplastic primary vitreous cases are unilateral, affecting only one eye ^11,12. In posterior PHPV, the globe is small and retinal detachment may be present.

Ultrasound

Ocular ultrasound may show an echogenic band in the posterior segment of the globe, extending from the posterior surface of the lens to the optic nerve head. On color Doppler, arterial blood flow may be seen within this band.

CT

The CT appearance can be quite variable ⁹. The described spectrum of CT findings includes ¹:

• soft-tissue replacement (infiltration) of the vitreous body

• retrolental soft tissue along the Cloquet canal:  a fine linear structure
  extending from the head of the optic nerve to the posterior surface of the lens ³

• absence of abnormal calcification within the orbit

• microphthalmos

• retrohyaloid layered blood

• hypervascularity of the vitreous humor: after contrast administration, the vitreal abnormalities may enhance, which is believed to reflect a persistent hypervascular vitreous

• retinal detachments can be hyperdense on CT

MRI

On MRI the retrolental tissue characteristic of this condition has a triangular shape resembling a martini glass, appearing as low T2 signal against the normal high T2 signal of the globe ¹⁰.

Differential diagnosis

• the differential diagnosis clinically is that of leucocoria, including congenital cataract, retinopathy of prematurity, Coats disease and retinoblastoma

  • PHPV is one of the more significant and frequent conditions that can mimic a retinoblastoma, with the presence of calcification being a key discriminating feature (calcification is almost always present in retinoblastoma)

  • retinopathy of prematurity is more commonly bilateral, PHPV is usually unilateral and would occur in full-term healthy infants ^11,12

• at ultrasound, the primary differential is of uncomplicated congenital cataract or retinal detachment, which is commonly associated with PHPV

  • PHPV can be distinguished from an uncomplicated congenital cataract by the presence of a fibrovascular stalk, an elongated ciliary process and a shallow anterior chamber ^11,12