RADIOLOGY CORNER

Military Medicine, Feb 2008 by Warnock, Alicia, Gibson, Michael S, Folio, Les R

Answer to last month's radiology case and image: Chondroblastoma with Secondary Aneurysmal Bone Cyst

(Case #21 appears at the end of this article)

History

A 24 year old active duty male presents to his provider with right-sided, lower posterior chest wall rib pain for approximately 4-6 months, which has been increasing in severity. He notes that the pain increases with deep inspiration. He denies a history of trauma in the area. On physical exam, right paraspinal tenderness upon palpation is present, approximated at the 9th posterior rib.

The authors present a case that highlights the utility of a basic search pattern for chest radiographs, with attention to the silhouette sign (or lack thereof). Our case demonstrates how to localize a mass on chest radiography using PA and lateral views, and provides an example of the imaging workup of a mass seen on chest radiograph. Although our case is rare, the plain radiographic findings and imaging workup in this case are fundamental concepts.

Summary of Findings

The chest x-ray (see previous issue of Military Medicine or full-text version on -line) demonstrates a large opacity visible in right lung field, at level of the right hilum. The density has fairly well delineated borders superiorly and interiorly, but becomes patchy laterally. The lesion does not silhouette the right heart border. The medial aspect of the posterior right 9th rib is poorly defined. Axial T2W MR (fig. 1) demonstrates a large, lobulated mass located in the right paraspinal region, at the costovertebral junction of T9 and appears to originate from the ninth rib. The mass invades the right pedicle of T9 and extends into the neural foramen, where it abuts the thecal sac. Multiple fluid-fluid levels are present. Coronal T2W MR (fig. 2A) demonstrates a right paraspinal mass spanning levels T8-T10, with invasion of the right pedicle of T9. Coronal reconstructed CT image (fig. 2B) displays the lesion arising from the posterior right 9th rib.

Diagnosis

Chondroblastoma with Secondary Aneurysmal Bone Cyst

Patient discussion: Paraspinal masses invoke an enormous list of differential diagnoses: lymphoma, metastatic disease, nerve sheath tumors, primary bone tumors, myeloma, meningocele, cysts, abscesses, posterior mediastinal masses and beyond. Location, radiographic features, and patient age are the initial diagnostics clues used to further narrow the diagnosis. Based on these parameters, with radiologic features of utmost importance, this particular patient's findings suggested a neoplastic process, which directed him to biopsy. Indeed biopsy results initially indicated that a primary bone neoplasm was credible, based on presence of osteoblasts and cartilage.

Primary bone tumors are relatively rare, with an incidence of approximately 10,000 cases a year in the US. Using the patient's demographics, radiographic features, and the confirmed presence of cartilage and osteoblasts, likely neoplasms include several benign primary bone tumors, malignant primary bone tumors, as well as neoplasms of alternate tissue origin, such as aneurysmal bone cysts and neurogenic tumors.

Final pathology reading of the resected specimen revealed a diagnosis of chondroblastoma with areas of secondary aneurysmal bone cyst. This is a very rare tumor, and even rarer is the location of the tumor in this patient.

The full text version is available in a downloadable PDF file on the AMSUS page of the USUHS website at:

http://rad.usuhs.mil/amsus.html

Category 1 CME or CNE can be obtained on this case of the week in the MedPix(TM) digital teaching file following this link.

References:

1 Attar, Ugur, Caglar, Erdogen, Ozdemir. Chondroblastoma of the thoracicvertebra. Journal of Clinical Neuroscience. 2001. 8(1); 59-60

2 Bullough, Peter. Orthopaedic Pathologv (third edition). Times Mirror International Publishers Limited: London, 1997.

3 Fines, Bonnie and Stacey, Gregory. Chondroblastoma, Radiology, Musculoskeletal. EMedicine Online. Last updated July 19, 2006. Accessed on March 2, 2007.

4 Gitelis, S. et al. Benign Bone Tumors. Instructional Course Lectures, 45:p. 426-46, 1991. Accessed via EMedicine on 2/26/07.

Contributors: LT Alicia Warnock, USN1; LCDR Michael S. Gibson, MC, USN1,2; COL Les R. Folio, USAF, MC, SFS1,2

1 Uniformed Services University, Bethesda, MD; National Naval Medical Center. Bethesda, MD

The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Uniformed Services University of the Health Sciences or the Department of Defense. Reprint & Copyright � by Association of Military Surgeons of U.S., 2006 .