Combined hamartoma of the retina and retinal pigment epithelium – MRI features of a rare paediatric intraocular tumour

Combined hamartoma of the retina and retinal pigment epithelium is a rare benign ocular tumour in children, composed of glial cells, vascular tissue, and sheets of pigmented epithelial cells. Although generally thought to be congenital, acquired cases are known to exist. It usually presents with reduced visual acuity and/or strabismus and it can be associated with several syndromes, including Neurofibromatosis Type 2. There is no consensus on the management of combined hamartoma of the retina and retinal pigment epithelium. We present a case, including MRI features, of a 4,5-years-old girl with a combined hamartoma of the retina and retinal pigment epithelium.


CLINICAL PRESENTATION
A 4,5-years-old girl was referred by her paediatrician for a brain MRI because of a new ocular motility disorder affecting her right eye. The girl has already been examined ophthalmologically from an early age because of a relative amblyopia of her right eye. At that time, she was diagnosed with Bergmeister's papilla. Bergmeister's papilla is a harmless variant of the papilla formed by a posterior remnant of the hyaloid artery presenting as an epipapillary membrane. The patient was otherwise healthy.

INVESTIGATIONS/IMAGING FINDINGS
An MRI with a specific orbital protocol was conducted (thin-slice coronal T 1 W and T 2 W fs, axial T 2 W, coronal and axial post-contrast T 1 W fs). It revealed a plaqueshaped lesion immediately in front of the papilla of the right eye. The lesion was about 6 mm wide, wider than the width of the papilla, and less than 1 mm thick ( Figure 1). On T 1 W and T 2 W images it was almost isointense to the optic nerve. On T 1 W images using fat saturation and contrast agent, a discrete enhancement could be assumed ( Figure 2). Between the lesion and the papilla, there was a very thin layer with isointense signal on T 2 W images to the vitreous body and enhancement being the normal choroid underneath the affected retina. There were no signs of calcifications. The eye size was normal compared to the contralateral eye. The rest of the right eye, the entire left eye, the optic nerves, and the rest of the brain MRI were normal. No explanation for the eye motility disorder could be found.
After the MRI, an ophthalmological examination, including fundoscopy and optical coherence tomography, was carried out by a paediatric ophthalmologist, and the diagnosis of a combined hamartoma of the retina and retinal pigment epithelium (CHR-RPE) was made (Figure 3a and b).

DIFFERENTIAL DIAGNOSIS
The radiological differential diagnosis of unilateral papillary or peripapillary mass or disk swelling in the first decade of life is broad and also includes the pathologies mentioned below: • Optic nerve drusen: they are limited to the papilla and can calcify. CHR-RPE is almost always solitary and unilateral. It usually presents during childhood (median age 7.5 year) with reduced acuity (40%) and/or strabismus (28%). 5,6 It can occur in the macula (17%), juxtapapillary (76%), or in the peripheral retina (7%). 7 Visual acuity varies with the location of the lesion. When located in the macula, it can cause significant vision loss. 6 The majority of CHR-RPE occurs sporadically. However, it has been reported to occur in association with neurofibromatosis Types 1 and 2, tuberous sclerosis, Gorlin syndrome, branchio-oculo-facial syndrome, nasopharyngeal angiofibroma, and Poland syndrome. [8][9][10][11][12][13][14] One author has even recommended to screen children with CHR-RPE for NF-2.
An ophthalmologist with paediatric experience will be able to diagnose a CHR-RPE. Because of its rarity and variable clinical appearance, misdiagnoses are common and include melanoma, retinoblastoma, Bergmeister's papilla (as in our case), congenital hypertrophy of the RPE, or vascular anomaly. Early stages of this tumour can mimic disk swelling.
The diagnosis cannot be made using radiological imaging alone. We believe that radiology is primarily useful to rule out other causes and to look for any findings of the abovementioned associated syndromes that remain hidden from the ophthalmologist.

MANAGEMENT
There is no established consensus on the management of CHR-RPE. Surgical interventions (vitrectomy and membrane peeling) can be considered when the child is of amblyopic age, or when the visual acuity declines significantly. A visual improvement rate of 60% has been reported after surgery. Unfortunately, the epiretinal membrane often recurs and subsequent surgery tends to be increasingly less effective due to permanent architectural changes. 15 Our patient received no treatment. An ophthalmologic check-up is planned every 3 months due to the associated strabismus. At the last routine check-up in July 2020, there was no change in the fundoscopic findings.

LEARNING POINTS
• CHR-RPE is a rare benign ocular tumour in children.