Contributed by Hilary Somerset, MD1; C. Corbett Wilkinson, MD2; B.K. Kleinschmidt-DeMasters, MD1,3,4
1 Department of Pathology, University of Colorado Denver, Aurora, CO, 2Department of Neurosurgery, The Children's Hospital, Aurora, CO, 3Department of Neurology, University of Colorado Denver, Aurora, CO, 4Department of Neurosurgery, University of Colorado Denver, Aurora, CO
An 18-year-old nationally-ranked motocross rider presented to the hospital after crashing her motorbike in practice and tumbling over the handlebars. The patient hit her helmeted head on the ground, lost consciousness for a few seconds and then woke up confused. She was taken to the emergency room and observed overnight. Her confusion quickly resolved and her neurological exam was normal. Prior to this accident she did not have any neurological symptoms or significant medical history.
In addition to a linear right temporal skull fracture, head computed tomography (CT) incidentally revealed an inhomogeneously-hyperdense right frontal subdural lesion (2.9 x 2.9 x 1.3 cm) (Figure 1). Magnetic resonance imaging (MRI) characterized the lesion as isointense on T1-weighted images, hyperdense on T2-weighted images, and minimally-enhancing (Figure 2). The clinicians and family elected to observe the lesion given its extra-axial location and innocuous appearance on imaging. Over the next year and a half the patient remained asymptomatic but the lesion demonstrated slow growth on MRI; therefore, the patient elected to undergo surgery for removal of the mass. At surgery, the lesion was fused to the dura but easily separated from the brain. Gross examination showed a firm, glistening, pearly-white lesion with an irregular bosselated surface (Figure 3). It was attached to dura and the inner surface of the dura demonstrated no neomembrane or hemosiderin pigment staining (Figure 4). Cut section showed a largely homogenous white glistening tumor with lobularity and central yellowish partial cystic degeneration; there was no evidence of hemorrhage or necrosis (Figure 5).
Whole mount section further illustrated the central cystic degeneration and paralleled the gross appearance (Figure 6). Microscopic examination showed lobulated sheets of mature hyaline cartilage punctuated by single chondrocytes in small lacunar spaces with a background of abundant blue-gray chondroid matrix (Figure 7). The chondrocytes displayed bland cytological features (Figure 8) and undetectable mitotic activity. Areas of cytologic atypia, hypercellularity or multinucleation were not identified. There was a discrete demarcation between the cartilage and overlying dura; no areas of infiltration of dura or metaplasia within dura were seen. No hemosiderin pigment was present in subdural areas to suggest a remote subdural hematoma and no neomembrane was present. Centrally within the mass there were small hypocellular areas of myxoid degeneration containing loose fibrovascular tissue with histiocytes (Figure 9), which were CD68 immunoreactive and S100 negative. There was no osteogenic component.