Pediatr Blood Cancer 2013;60:E143–E145 Radiological Features of Thymic Langerhans Cell Histiocytosis Karoly Lakatos, 1 Heidrun Herbru ¨ ggen, 2 Ulrike Po ¨ tschger, 2 Helmut Prosch, 3 and Milen Minkov 2,4 * INTRODUCTION Langerhans cell histiocytosis (LCH) is a rare disease character- ized by proliferation of clonal dendritic cells [1,2]. It may affect virtually any organ and its clinical manifestations range from a single bony lesion to multi-system disease. Single cases and small series [3–7] document thymus involvement (TI) by LCH but its frequency is still unknown. This article presents results of a retrospective search for TI in a LCH database with a particular focus on radiological findings. PATIENTS AND METHODS The cohort included 1,264 patients with LCH enrolled into the consecutive international studies LCH-I, LCH-II, and LCH-III by 62 institutions of the German Society for Pediatric Hematology and Oncology (GPOH) between 1992 and 2009. Inclusion criteria were biopsy-proven LCH, age <18 years, no earlier treatment for LCH and written informed consent. All patients had standardized initial evaluation including chest radiography. As routine thymus imaging was not part of the patient evaluation, the database was screened for incidental reporting of TI. Images of the thymus were collected and centrally reviewed by two experienced radiologists with emphasis on thymus size, texture, cysts, and calcifications. Thymus size was assessed at maximum transverse width [8]. Calcifications were semi-quantitatively categorized as:þfew (singular dot-like); þþsome; þþþmany (extensive, coarse). Cysts were classified as: þfew (<10) or þþmany (>10). Eighteen patients with TI were identified, 15 of them had sufficient clinical information and images available for review. One patient (case 3) has been previously published for his instructive clinical course [9]. We looked for association between TI and age and disease extent for the 15 patients only. Three histology reports from thymus biopsy were available, two of them confirming active LCH lesions and one (fine-needle biopsy) revealing unspecific inflammatory changes. RESULTS Prevalence of TI Eighteen patients (18/1,264; 1.4%) were reported to have TI. The population characteristics of the 15 patients with TI and available clinical and imaging information are summarized in a Supplementary Table. TI was diagnosed at initial LCH presentation (n ¼ 9) or developed later (n ¼ 6). TI at initial disease presentation was seen exclusively in patients with multisystem LCH (9/397, 2% MS-LCH vs. 0/867 SS-LCH; P < 0.001). All nine patients were below 2 years of age at LCH presentation (9/242, 4% vs. 0/155; P < 0.015). Among those who developed TI later, only one had at initial disease presentation single-system LCH (isolated skin disease). At the time TI was detected all patients had active disease in at least one additional organ, and thus were classified as MS- LCH. The clinical course of LCH in the 15 patients with available clinical information is presented in a Supplementary Figure. Imaging Findings The findings based on the first available thymus images are presented in Table I. Ten patients (67%) had an enlarged thymus. Few or many cysts with a diameter of up to 7 mm were present in 12 patients (80%). Few, some or many calcifications were present in 15 patients (100%). SONOGRAPHY Affected thymus appeared inhomogeneous with some to many calcifications (Fig. 1A) and few to many hypoechogenic cysts up to 4–5 mm in diameter. CT Affected thymus appeared inhomogeneous containing hypo- dense (cysts) and hyperdense (calcifications) areas as compared to muscle density. Calcifications (Fig. 1B) varied from few to many. In five of seven cases many well defined, round to oval cysts with a TI was reported in 18/1,264 (1.4%) LCH patients. All nine patients with TI at initial LCH presentation were below 2 years of age and had multisystem LCH (9/242, 4%). Images (sonography, CT, MRI) for central review were available in 15 cases. Characteristic findings of TI were thymus enlargement (67%), few to many cysts (80%), and few to many calcifications (100%). Sonographic and MRI findings were in excellent agreement. We recommend adding sonography of the thymus to the standard for initial clinical evaluation of LCH patients below the age of 2 years. Pediatr Blood Cancer 2013;60:E143–E145. # 2013 Wiley Periodicals, Inc. Key words: histiocytosis X; imaging; sonography; thymus Additional Supporting information may be found in the online version of this article at the publisher’s web-site. 1 Department of Radiology, St. Anna Children’s Hospital, University Clinic of Pediatrics, Medical University of Vienna, Vienna, Austria; 2 Department S2IRP, Children’s Cancer Research Institute, Vienna, Austria; 3 University Clinic of Radiology, Medical University of Vienna, Vienna, Austria; 4 Department of Hematology/Oncology, St. Anna Children’s Hospital, University Clinic of Pediatrics, Medical University of Vienna, Vienna, Austria Conflict of interest: Nothing to declare.  Correspondence to: Milen Minkov, Department of Pediatrics, St. Anna Children’s Hospital, University Clinic of Pediatrics, Medical University of Vienna, Kinderspitalgasse 6 A-1090 Vienna, Austria. Email: milen.minkov@stanna.at Received 24 November 2012; Accepted 13 May 2013  C 2013 Wiley Periodicals, Inc. DOI 10.1002/pbc.24640 Published online 29 June 2013 in Wiley Online Library (wileyonlinelibrary.com).