Peripapillary Hyperreflective Ovoid Mass-Like Structures (PHOMS)

Introduction

Peripapillary Hyperreflective Ovoid Mass-Like Structures (PHOMS) are homogenous rounded structures, recently described in latest studies regarding Optic Nerve Head (ONH) evaluation. They were traditionally considered as a subtype of Optic Disc Drusen (ODD). However, the Optic Disc Drusen Studies (ODDS) Consortium, a group of fellowship trained neuroophthalmologists and researchers, ellaborated a recent work using Enhanced-Depth Imaging Optical Coherence Tomography (EDI-OCT) of ODD patients, in which they considered that PHOMS shouldn’t be diagnosed as ODD . PHOMS is increasingly thought to correspond to axoplasmic stasis and nerve fiber buldging/herniation in peripapillary region, assuming the shape of a “doughnut” or torus around ONH.

Historical Background

Previous studies regarding the evaluation of morphologic characteristics of ODD as visualized using Spectral-Domain Optical Coherence Tomography (SD-OCT) tried to categorize them into two types – visible and buried – according to their position related to ONH. The former were located mostly inside the disc and were characterized by highly reflective borders with internal hyporreflective core (“cysts”) and RNFL thinning, often existing as multiple lumps, sometimes coalescing in bigger. Buried optic nerve head drusen were located exclusively outside ONH and were characterized by an amorphous C-shaped mass that had relatively less distinct borders .

Etiology

PHOMS can be present in various clinical situations such as :

  1. Papilledema,
  2. Anterior Ischaemic Optic Neuropathy (AION),
  3. Central Retinal Vein Occlusion (CRVO),
  4. Optic Neuritis (ON),
  5. Tilted-Disc Syndrome (TDS),
  6. Optic Disc Drusen (ODD).


Thus, PHOMS is an unspecific finding, can be related to true disc edema or cases of pseudopapilledema and usually resolves with its underlying condition/etiology.

Definition

ODDS Consortium Recomendations

Malmqvist et. al showed in 2018 that PHOMS were present in 74% of patients with ODD included on their analysis. They stated that, in spite of their histopathological relationship not being clear, there were several features that appeared to distinguish them from each other:

  • Unlike ODD, PHOMS are hyperreflective without a sharp outer margin or hyporeflective core;
  • PHOMS often lie external to and surrounding large parts of the disc, corresponding to funduscopically recognized pseudopapilledema;
  • PHOMS don’t autofluoresce;
  • PHOMS are not visible on B-scan ultrasound despite their superficial location;
  • PHOMS can be seen in patients with papilledema without ODD;
  • Histopathology of papilledema suggests that PHOMS might correspond to the lateral bulging or herniation of distended axons into the peripapillary retina.


Thus, PHOMS shouldn’t be diagnosed as ODD, unless there was histopathological evidence to the contrary.

Multirater Validation of PHOMS

Since PHOMS’ related papers increased since ODDS Consortium Recomendations publication, accuracy of the definition and reliability of diagnosis of PHOMS turned out to be innefective and resulted in a poor interobserver agreement. In order to attain better level of agreement among physicians, another group of experts performed a Delphi consensus process to develop a consistent and refined definition of PHOMS, focused on 3 caracteristic found on OCT B-Scans:

  1. Location: strictly peripapillary and sitting on top of Bruch’s membrane. Frequently; a gap can be observed in the B-scan scans of PHOMS aligned through the centre of the optic disc;
  2. Effect on adjacent retinal layers: an upward deflection of at least two of the other retinal layers;
  3. Signal appearance: similar to the reflectivity to the retinal nerve fibre and ganglion cell layers.

 

Diagnostic Modalities

EDI-OCT

 
Multimodal Imaging of PHOMS.

PHOMS was firstly described as a finding on EDI-OCT images of patients with ODD. The resemblance of PHOMS with the histopathology sample of a patient with papilledema (lateral buldging/herniation of RNFL) brought out the idea that both findings could be related with axoplasmic stasis.

A retrospective cohort that studied 64 eyes (32 patients, children with 5-16 years) suspected of having pseudopapilledema (normal RNFL thickness, without disc swelling appearance on fundoscopy) found out that 93.8% of eyes with PHOMS exclusively had small hyperreflective foci inside, indicating that it might contain calcium deposits in its composition. This finding supported the thesis that PHOMS and ODD might represent a spectrum of the same disease, with PHOMS representing continued axoplasmic stasis, leading to extrusion of calcified mitochondria, calcium deposition and formation of drusen ODD. They had also identified a distinct ring sign visible on the infrared images of all cases of PHOMS, corresponding to the edge of the structure as seen EDI-OCT.

 

File:PHOMS multimodal imaging.png

Infrared image (a) showing a ring (arrow) temporal to the optic disc, correlating with the exact location of the PHOMS edge shown on EDI-OCT in (c). The PHOMS contains small hyperautofluorescent spots seen on fundus autofluorescence (FAF) (b, encircled), and hyperreflective spots on the infrared images (c, encircled). d – Ultrasound B-scan showing a hyperechogenic structure (arrow) at the optic nerve head, correlating with the PHOMS seen on EDI-OCT.

 

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Retina Ward of Farabi Eye Hospital