CASE 15372 Published on 02.03.2018

Giant reservoir formation as a complication of an Ahmed glaucoma valve device

Section

Head & neck imaging

Case Type

Clinical Cases

Authors

Hernan Nova-Escobar 1, Vanessa Bornacelli-Barreneche 2, Carolina Diaz-Angulo 3

1: Radiology Resident, PGY 3, Universidad del Norte.
2: Radiology Resident, PGY 2, Universidad del Norte.
3: Radiologist, Barranquilla, Colombia.

Email:hernannova@gmail.com
Patient

32 years, male

Categories
Area of Interest Eyes ; Imaging Technique Neural networks, Image manipulation / Reconstruction, MR
Clinical History
A 32-year-old man complained of progressive visual loss and pain of the left eye for 1 week. Past medical history revealed previous Ahmed glaucoma valve (AGV) implantation for refractory glaucoma 8 months ago.
AGV are made of silicon and considered MR compatible. An MRI examination was therefore performed.
Imaging Findings
Models of AGVs are shown in Fig 1a. Normal ocular anatomy demonstrating correct AGV positioning and normal flow is demonstrated in Figs 1b-c.

Figs 2a-b and Figures 3a-c reveal an ovoid, thin-walled, cystic lesion in the superotemporal quadrant of the left orbit. This demonstrates TIW isointensity and T2W hyperintensity. Note how the lesion contains a centrally located low signal curvilinear band on both T1- and T2-weighted images (yellow arrows) representing the silicone end-plate of the Ahmed device.

No enhancement was evident following iv contrast administration and no pathological soft tissue enhancement was seen (Figs 4a-b).

MR imaging demonstrates a large fluid collection representing a giant reservoir, surrounding the end-plate of the AGV implant that resembles the appearance of the meringue-based sweet, macaroon.

Figs 5a and b compare a normally functioning Ahmed device (blue arrows) with the patient in this case report suffering complications (white arrows).
Discussion
Glaucoma is the third most common cause of irreversible visual loss in adults in the United States [1]. Elevated intraocular-pressure (IOP) leads to progressive optic nerve injury and loss of peripheral vision [2]. Lowering IOP is the mainstay of treatment [1, 3].

First line treatment consists of medical therapy. Surgical options such as glaucoma drainage devices may provide an alternative in complicated and refractory glaucoma [2, 4].

Glaucoma drainage devices (GDDs) were previously reserved for cases where medical therapy or simple surgery was insufficient, but are now being used more frequently. The preferred procedure is to implant the GDD in the superotemporal or inferonasal quadrant of the orbit [1]. Implantation in the superonasal quadrant is not recommended to avoid Brown syndrome (an inability to elevate the adducted eye secondary to injury of the superior-oblique tendon sheath complex) [1, 5].

GDDs comprise of two parts; a tube and a plate. One end of the tube is placed into the posterior segment, anterior or posterior chamber of the globe. The other end is attached to the plate portion of the implant, placed in the subconjunctival space where periocular vasculature reabsorbs aqueous humour into the systemic circulation [2].

Several types of GDD exist, varying in size, materials, and pressure resistance to aqueous humour flow [5]. The most commonly used are: Molteno, Baerveldt (radiopaque on radiographs due to barium-impregnated silicone), Krupin and Ahmed. Krupin and Ahmed devices use a unidirectional valve with leaflets that limit flow and prevent hypotony [1, 3]. Successful treatment is defined as post-operative IOP greater than 5 mmHg and less than 22mmHg without complications [2, 6].

A fibrous-encapsulated bleb is a late complication formed at the plate portion of GDDs, which may simulate a cystic lesion[1]. Encapsulated blebs prevent normal aqueous humour flow, resulting in IOP elevation and expansion of the AGD [4]. The smaller surface area and immediate fluid filtration of the AGD may predispose to a higher incidence of encapsulation [2, 3]. On MRI blebs present with variable sized T2W 'cysts'. Giant reservoirs appear as an ovoid cyst in the superotemporal border of the orbit near the lacrimal gland, with thin walls probably formed by the fibroid pseudocapsule with a silicone endplate band in the center, hypointense on T1 and T2W imaging [4].

Digital massage and antifibrotic medication can reduce the size of the reservoir, however surgical scar tissue removal to allow aqueous humor flow is considered in resistant cases [4].
Differential Diagnosis List
Giant reservoir formation - A complication of surgical treatment of glaucoma
Dermoid cyst
Lymphangioma
Lacrimal gland cyst
Abscess
Final Diagnosis
Giant reservoir formation - A complication of surgical treatment of glaucoma
Case information
URL: https://www.eurorad.org/case/15372
DOI: 10.1594/EURORAD/CASE.15372
ISSN: 1563-4086
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