CLINICAL REPORT PEDIATRICS CT andMRI of Pediatric Skull Lesions with Fluid-Fluid Levels

SUMMARY: Fluid-fluid levels can occur whenever different fluid densities are contained within a cystic or compartmentalized lesion, usually related to the evolution of hematoma or necrosis. Review of the literature demonstrated that throughout the skeletal system, the most common etiology for fluid-fluid levels is aneurysmal bone cyst, but there are no dedicated studies of the pediatric calvaria, to our knowledge. In this report, we present clinicopathologic characteristics and CT and MR imaging of 11 patients with pediatric skull mass lesions demonstrating fluid-fluid levels. MR imaging demonstrated more fluid-fluid levels compared with CT in all cases. The etiologies of skull lesions with fluid-fluid levels were Langerhans cell histiocytosis in 4 (36.6%), aneurysmal bone cysts in 3 (27.2%), cephalohematoma in 3 (27.2%), and metastatic neuroblastoma in 1 (9%). Radiologists should be aware of the other etiologies of calvarial lesions with fluid-fluid levels in the pediatric skull. ABBREVIATIONS: ABC aneurysmal bone cyst; FFL fluid-fluid level; LCH Langerhans cell histiocytosis Fluid-fluid levels (FFLs) may occur whenever different fluid densities are contained within a cystic or compartmentalized structure, usually related to hemorrhage or necrosis. Image acquisition near perpendicular to the plane of the FFL is required to optimally demonstrate it. FFLs in skeletal lesions have been a well-known imaging feature of aneurysmal bone cyst (ABC) for many decades. To our knowledge, there is no dedicated study focusing on the different etiologies of FFLs in the pediatric population and there is no study focused on fluid-fluid levels in calvarial lesions. However, 2 large studies primarily in adult patients have demonstrated that ABCs are the most common etiology of osseous lesions with FFLs throughout the body. Despite these data, the presence of FFLs remains a nonspecific finding and can be seen in a wide range of benign and malignant bone lesions, including fibrous dysplasia, telangiectatic osteosarcoma, osteoblastoma, simple bone cyst, lymphatic malformations, Ewing sarcoma, brown tumor, giant cell tumor, and chondroblastoma. In this study, head CT and MR imaging of pediatric patients having skull lesions with FFLs were retrospectively reviewed with the aim of characterizing these lesions. CASE SERIES Patients The study was performed with approval of the institutional review board and was compliant with guidelines of the Health Insurance Portability and Accountability Act. We performed a retrospective review of records of pediatric patients with skull masses diagnosed between 2002 and 2012. Cases were ascertained from teaching files of the authors and a computerized search of the PACS for patients younger than 18 years of age who were diagnosed with a skull lesion showing fluid-fluid levels on CT or MR imaging. The search terms included various combinations and derivatives of “fluid-fluid,” “blood-fluid,” “fluid levels,” “skull,” and “calvarium.” Medical records were reviewed for patient age, sex, history of recent trauma to the lesion, history of coagulopathy, types of treatment, and histopathologic diagnosis. Patients with a history of surgery on the skull were excluded. The etiologic diagnosis was made by histopathologic examination of resected lesions in 6 patients and of biopsied specimens in 1 patient. In 3 patients who were classified as having cephalohematoma, the diagnosis was made on the basis of characteristic clinical presentation, history of traumatic vaginal delivery, and/or spontaneous resolution of the lesion by consensus of pediatric neuroradiologists and by review of medical records. Finally, 1 patient with primary neuroblastoma was diagnosed as having metastatic involvement of the skull on the basis of typical imaging findings of neuroblastoma both on CT and MR imaging and considerable improvement of the lesion after targeted chemotherapy. Received May 10, 2013; accepted after revision June 20. From the Department of Radiology, The Children’s Hospital of Philadelphia, University of Pennsylvania, Philadelphia, Pennsylvania. Please address correspondence to Seyed Ali Nabavizadeh, MD, Department of Radiology, The Children’s Hospital of Philadelphia, University of Pennsylvania, 34th and Civic Center Blvd, Philadelphia, PA 19104; e-mail: nabavizadehs@email.chop.edu http://dx.doi.org/10.3174/ajnr.A3712 604 Nabavizadeh Mar 2014 www.ajnr.org CT and MR Imaging CT was performed on various multidetector CT scanners (Siemens, Erlangen, Germany), and MR imaging was performed on 1.5T or 3T magnets (Siemens) with standard clinical protocols used at the time of the study. Axial CT sections were reconstructed at 3or 5-mm thicknesses. MR imaging sequences varied among patients but generally included preand postcontrast T1-weighted, T2-weighted, fluid-attenuated inversion recovery, echo-planar spin-echo diffusionweighted imaging, and either T2* gradient-echo susceptibility or susceptibility-weighted imaging. The CT and MR imaging studies of these patients were reviewed by 2 pediatric neuroradiologists by consensus, and the findings were tabulated. For each scan, lesion location, number of fluid-fluid levels, and the presence or absence of soft-tissue components were evaluated. Diagnosis of hemorrhage was based on hyperattenuation on noncontrast CT or typical MR imaging findings (mainly hyperintensity on T1-weighted, hypointensity on T2-weighted, and/or susceptibility on gradient-echo or susceptibilityweighted images). Clinicopathologic and Imaging Findings Eleven patients (6 male, 5 female) with skull lesions showing fluid-fluid levels met the inclusion and exclusion criteria (Table). The mean age of patients at the time of primary diagnosis was 6.2 6.1 years (range, 8 days to 16 years). The etiologies of the lesions included Langerhans cell histiocytosis (LCH) (n 4[36.6%]),aneurysmalbonecyst (n 3 [27.2%]), cephalohematoma (n 3 [27.2%]), and neuroblastoma (n 1 [9%]). In 7 patients, both CT (4 noncontrast, 3 contrast-enhanced) and MR imaging with and without contrast were performed. MR imaging with and without contrast was the only imaging technique in another 4 patients. In the 7 patients in whom a CT had been performed, FFLs were identified in 6 patients (85%). The mean number of fluidfluid levels detected on CT was 3.5 3.2 (range, 1–9). FFLs were present on MR imaging in all 11 patients (100%). The mean number of detected fluid-fluid levels on MR imaging was 9.2 9.1 (range, 1–29). The number of observed FFLs was significantly higher on MR imaging compared with CT (Z 2.36, Wilcoxon signed-rank test,