Symptomatic vertebral hemangiomas: MR findings.

Abstract

V ertebral hemangiomas are common benign lesions of the spinal column that often are discovered incidentally. Rarely, vertebral hemangiomas behave as aggressive neoplasms that directly or indirectly compress adjacent neural structures. The diagnosis of symptomatic lesions can be elusive on any imaging study but can be especially difficult on MR imaging studies. Because symptomatic hemangiomas typically show marked hypervascularity on spinal angiography, knowledge of the diagnosis before biopsy or surgery is invaluable. The purpose of this essay is to highlight the MR findings in representative cases of symptomatic hemangiomas and to provide clues that may distinguish them from other, more common neoplasms. Moreover, in an era dominated by the use of MR imaging for the evaluation of myelopathy, the importance of basic diagnostic radiologic examinations (plain radiographs and CT scans) in the evaluation of vertebral neoplasms should not be overlooked. Hemangiomas are slowly growing lesions that are commonly found in the vertebral bodies. Histopathologically, they consist of thinwalled, blood-filled vessels and sinuses lined by endothelium and interspersed among the longitudinally (vertically) oriented trabeculae of bones. The dilated vascular channels are set in a substratum of fatty marrow. The accumulation of lipid material is a common secondary and retrogressive phenomenon seen in several types of benign bone lesions. Characteristic plain radiographic findings for asymptomatic vertebral hemangiomas consist of either parallel linear streaks or a honeycomb pattern. CT scans show a speckled (“polka dot”) pattern because the accentuated vertical trabeculae are imaged in cross section [ 1-5]. Asymptomatic vertebral hemangiomas classically show a distinctive appearance on MR images; high signal intensity is seen on spin-echo T I -weighted and T2-weighted images. The shortened Tl relaxation time reflects the fatty component of the tumors. Because fat shows a high signal intensity on T2-weighted fast spin-echo MR images, vertebral hemangiomas remain hyperintense with this pulse sequence [1]. Symptomatic (compressive) vertebral hemangiomas are rare lesions that can gradually compress the spinal cord, nerve roots, or both, thereby producing myelopathy or racliculopathy [1-8]. Compression of neural elements may be related to vertebral fracture, extraosseous extension of the tumor or, less frequently, enlargement of adjacent blood yessels (Figs. 1-4). Diagnosis of these lesions may be much more elusive than that of asymptomatic hemangiomas because many of the aforementioned radiographic characteristics may be absent [ 1-8]. Because MR imaging does not directly visualize bone, the diagnosis can be particularly difficult with this imaging technique. Moreover, in the current era, plain films and CT scans may not be obtained for the evaluation of patients with myelopathy. Ninety percent of vertebral hemangiomas having extraosseous extension occur in the thoracic region; approximately 75% occur between T3 and T9 (Figs. 1-3). A slight predominance in women exists. Cervical lesions are extremely rare [2, 6]. Other authors have described an inverse relationship between the amount of intraosseous fatty stroma and the aggressiveness of the lesion; this relationship accounts for the low signal intensity of most compressive vertebral hemangiomas on Tl-weighted images [6] (Figs. 1 and 3). Consequently, multiple lesions can simulate metastatic disease [SI (Fig. I). Although extremely unusual, an extensive amount of intraosseous fatty stroma and extraosseous extension of a neoplasm can occur simultaneously (Fig. 2); in these cases,