Retinoblastoma Imaging

Retinoblastoma Imaging Dear Editor: In the August 2009 issue of Ophthalmology, Dr Wilson et al1 published a retrospective study assessing the reliability of magnetic resonance imaging (MRI) in the management of retinoblastoma. The authors correlated the histologic features and the MRI findings of the optic nerve in children primarily enucleated. The authors concluded that “limited correlation was found between MRI and histologic results in assessing optic nerve invasion,” and that “the interpretation of optic nerve involvement by a radiologist should not be the determining factor to defer enucleation in favor of neoadjuvant therapy.” Since the main objective of preoperative MRI is to assess the optic nerve, the Wilson et al report leads to some important questions and clarification, which will help to avoid any misunderstanding about the role and accuracy of this technique. Pathology remains the gold standard to assess high-risk features of retinoblastoma. However, incomplete resection of tumors with extraocular extension is known to be associated with a high relapse risk, and therefore requires intensified treatment including chemotherapy and radiotherapy. Imaging is able to depict such extraocular extensions, notably within optic nerve, and among the available imaging techniques, MRI is now widely considered to be the most accurate one.2– 4 Moreover, the treatment options for unilateral retinoblastomas significantly improved during the past years and now include neoadjuvant chemotherapy for either conservative treatment or locally advanced tumors. Intra-arterial infusion of melphalan is also a recent additional treatment option for advanced diseases.5 In such circumstances, the pathologic gold standard cannot be obtained, underlying the major role of imaging at the time of diagnosis for local staging. The methods used by the authors to reach their conclusions are debatable. High-resolution imaging must be used to assess the anatomic details of the papilla, lamina cribrosa, and pre- and postlaminar segments of the optic nerve. In the study by Wilson et al, routine MRI protocols were used, including only head coils, 3-mm slice thickness, 5122 or 2562 matrix and obviously large fields of view. Such protocols lead to in-plane pixel size of 0.5 to 1 mm or even more. From a basic technical point of view, it is not possible to assess details measuring less than 1 mm with such resolution. Because of this limitation, in a recent retrospective series,2 other authors only focused on postlaminar involvement and demonstrated a 60% sensitivity and 95% specificity of MRI. The continuous improvement of MRI units and the use of small fields of view with either multiple channel head coils or orbit surface coils now allows much higher spatial resolution (about 0.3 mm in-plane pixel size with 2- or 1.5-mm slice thickness) allowing depiction of many subtle details around the lamina cribrosa. Initial results were published in 2007 by Lemke,4 and it is anticipated that ongoing studies will confirm these results.

One conclusion of the authors is that “MRI has limited usefulness in assessing the exact extent of optic nerve invasion.” However, when postlaminar invasion is suspected on preoperative MRI, one major issue is to assess the length of the involved nerve in order to estimate the risk of involvement of the nerve cut-section.2 Unfortunately, no correlation between the length of optic nerve enhancement on MRI and retrolaminar invasion length at pathology were provided in Wilson’s study. Wilson et al also did not provide the imaging criteria used to define prelaminar versus intralaminar or versus postlaminar tumor invasion, although postlaminar invasion criteria were previously published.2 This methodological bias probably explains the low agreement observed between the 2 readers, as well as the discrepancies between imaging and pathologic findings. The Figure 1B (incorrectly described as “fat saturated”) was supposed to demonstrate a “false positive” MRI result with “laminar and postlaminar invasion” according to “both neuroradiologists.” However, since no enhancement can be depicted behind the level of the lamina cribrosa, according to the criteria published in the literature, such pattern should not be interpreted as postlaminar optic nerve invasion. In conclusion, we believe MRI using high-resolution protocols is currently the most reliable imaging method to assess local extension of retinoblastoma. Brain MRI should also be systematically performed to depict possible associated midline CNS tumors (PNET) or CNS malformations. The Wilson et al report should not discourage ophthalmologists and radiologists from using this valuable diagnostic tool. HERVÉ J. BRISSE, MD, PHD Paris, France on behalf of the European Retinoblastoma Imaging Collaboration (Appendix 1; available at http://aaojournal.org) References 1. Wilson MW, Rodriguez-Galindo C, Billups C, et al. Lack of correlation between the histologic and magnetic resonance imaging results of optic nerve involvement in eyes primarily enucleated for retinoblastoma. Ophthalmology 2009;116:1558 – 63. 2. Brisse HJ, Guesmi M, Aerts I, et al. Relevance of CT and MRI in retinoblastoma for the diagnosis of postlaminar invasion with normal-size optic nerve: a retrospective study of 150 patients with histological comparison. Pediatr Radiol 2007;37: 649 –56. 3. de Graaf P, Barkhof F, Moll AC, et al. Retinoblastoma: MR imaging parameters in detection of tumor extent. Radiology 2005;235:197–207. 4. Lemke AJ, Kazi I, Mergner U, et al. Retinoblastoma-MR appearance using a surface coil in comparison with histopathological results. Eur Radiol 2007;17:49 – 60. 5. Abramson DH, Dunkel IJ, Brodie SE, et al. A phase I/II study of direct intraarterial (ophthalmic artery) chemotherapy with melphalan for intraocular retinoblastoma initial results. Ophthalmology 2008;115:1398 – 404, 1404 e1.

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Ophthalmology Volume 117, Number 5, May 2010

Appendix 1. Members of the European Retinoblastoma Imaging Collaboration (ERIC) Pr Dr Jonas A. Castelijns (Chair), Dr Pim de Graaf and Firazia Rodjan (Department of Radiology, VU University Medical Center, Amsterdam, The Netherlands), Hervé Brisse (Département d’Imagerie, Institut Curie, Paris, France), Dr Paolo Galluzzi (Neuroimaging and Neurointervention NINT, Azienda Ospedaliera e UNiversitaria Santa Maria alle Scotte

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Siena, Italy), Dr Sophia Göricke (Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Germany), Pr Dr Arne-Jörn Lemke (Radiologie und Neuroradiologie Städtisches Klinikum Dessau, DessauRoßlau, Germany) and Dr Philippe Maeder (Service de Radiodiagnostic et Radiologie Interventionnelle, CHUV, Lausanne, Switzerland). The European Retinoblastoma Imaging Collaboration (ERIC) is financially supported by The ODAS Foundation, Delft, The Netherlands.