122 SA JOURNAL OF RADIOLOGY • December 2010 SIGNS Case history A 9-month-old girl presented with a 1-month history of coughing. A chest X-ray (CXR) was performed, and the antero-posterior view demonstrated the hilum overlay sign. Furthermore, there was absence of the azygo-oesophageal line and bilateral paraspinal lines. The lateral CXR revealed a posterior mediastinal mass. Subsequently, a computed tomogram of the chest confirmed a posterior mediastinal mass, with calcifications and intraspinal extension consistent with neuroblastoma. Histological analysis confirmed this mass as a neuroblastoma. The sign Felson described the hilum overlay sign as the visualisation, on a frontal X-ray, of the first bifurcation of either the left or right pulmonary artery more than 1 cm medial to the lateral edge of the cardiac shadow. This is highly suggestive of a mediastinal mass.1,2 The hilum overlay sign is present on a frontal chest radiograph when normal hilar structures can be visualised through a mass, which implies that the mass is either anterior or posterior to the hilum.3 The presence or disruption of mediastinal lines may further aid in the localisation of The hilum overlay sign in a child M J van Wyk, MB ChB N Mahomed, MB BCh, FCRad (Diag) (SA) Department of Diagnostic Radiology, Chris Hani Baragwanath Hospital and University of the Witwatersrand, Johannesburg Fig. 1. AP CXR demonstrates the hilar overlay sign, with normal hilar structures visualised through the mass, and the absence of the azygo- oesophageal and bilateral paraspinal lines. Fig. 2. Lateral CXR confirms a posterior mediastinal mass. Fig. 3. Post-contrast axial chest CT at the level of the mediastinum demonstrates a poorly enhancing, predominantly right sided, posterior mediastinal mass with calcification and right neural foramen extension. SA JOURNAL OF RADIOLOGY • December 2010 123 SIGNS the mass. The absence of the paraspinal and azygo-oesophageal lines suggests that a mass is located in the posterior mediastinum. The sign also enables us to distinguish a mediastinal mass from a prominent cardiac silhouette.4 A typical posterior mediastinal mass displaying the hilum overlay sign is neurogenic in origin in the majority (88%) of cases.5 When there is calcification or adjacent bony erosion on a radiograph, it is highly suggestive of neuroblastoma.5,6 It may displace and invade adjacent structures and may even cross the midline.6 Most (70 - 90%) neuroblastomas usually occur in the first 5 years of life.5,6 1. Felson B. The mediastinum. Semin Roentgenol 1969;4:41-58. 2. Felson B. More chest roentgen signs and how to teach them. Annual oration in memory of L Henry Garland, M.D., 1903-1966. Radiology 1968;90:429-441. 3. Whitten CR, Khan S, Munneke GJ, Grubnic S. A diagnostic approach to mediastinal abnormalities. RadioGraphics 2007;27:657-671. 4. Lesslie M, Chasen MH, Munden RF. Imaging of the mediastinum in oncology. Applied Radiology 2007;36(1): 8-19. 5. Merten DF. Diagnostic imaging of mediastinal masses in children. AJR 1992;158:825-832. 6. Strollo DC, Rosado-de-Christenson ML, Jett JR. Primary mediastinal tumors part II: Tumors of the middle and posterior mediastinum. Chest 1997;112:1344-1357. Guidance on Prescribing Alimentary Tract and Metabolism Blood and Blood-forming Organs Cardiovascular System Dermatologicals Genitourinary System and Sex Hormones Systemic Hormonal Preparations General Anti-infectives for Systemic Use Antineoplastic and Immunomodulating Agents Musculoskeletal System Central Nervous System Antiparasitic Products Respiratory System Sensory Organs Contrast Media Treatment of Poisoning Published by the South African Medical Association, the formulary is aimed at doctors, pharmacists, nurses, dentists and others concerned with the safe and cost-effective prescribing of medicines. The South African Medicines Formulary is researched and written by members of the Division of Clinical Pharmacology of the University of Cape Town, in collaboration with health care professionals. The South African Medical Association, Health and Medical Publishing Group, Private Bag X1, Pinelands 7430 ISBN ���������������������������������� S o u th A fric a n M e d ic in e s F o rm u la ry Ninth Edition � NINTH EDITION Produced by the Division of Clinical Pharmacology, Faculty of Health Sciences, University of Cape Town. Published by the Health and Medical Publishing Group of the South African Medical Association. South African Medicines Formulary SAMF SAM F The ESSENTIAL REFERENCE for ever y healthcare professional! The carefully and thoroughly updated 9th edition of the South African Medicines Formulary (SAMF) can now be ordered. It is your essential reference to rational, safe and cost-efficient use of medicines. That is why you should not prescribe without it. The newly published SAMF provides easy access to the latest, most scientifically accurate information – including full drug profiles, clinical notes and special prescriber’s points. 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EMAIL: edwardm@hmpg.co.za OR byronm@hmpg.co.za Guidance on Prescribing Alimentary Tract and Metabolism Blood and Blood-forming Organs Cardiovascular System Dermatologicals Genitourinary System and Sex Hormones Systemic Hormonal Preparations General Anti-infectives for Systemic Use Antineoplastic and Immunomodulating AgentsMusculoskeletal System Central Nervous System Antiparasitic Products Respiratory System Sensory Organs Contrast Media Treatment of Poisoning Published by the South African Medical Association, the formulary is aimed at doctors, pharmacists, nurses, dentists and others concerned with the safe and cost-effective prescribing of medicines.The South African Medicines Formulary is researched and written by members of the Division of Clinical Pharmacology of the University of Cape Town, in collaboration with health care professionals. The South African Medical Association, Health and Medical Publishing Group, Private Bag X1, Pinelands 7430 ISBN ����������������� ����������������� S o u th A fric a n M e d ic in e s F o rm u la ry Ninth Edition � NINTH EDITIONProduced by the Division of Clinical Pharmacology, Faculty of Health Sciences, University of Cape Town. Published by the Health and Medical Publishing Group of the South African Medical Association. South African Medicines Formulary SAMF SAM F