Aneurysmal Bone Cyst 8.3.1
Definition, Epidemiology, Pattern of Growth
Aneurysmal bone cyst is a benign bone lesion characterized by several sponge-like, blood- or serum-filled, generally non-endothelialized spaces of various diameters. The first description dates back to the early 1940s (Jaffe and Lichtenstein 1942), but only in 1950 was the term aneurysmal bone cyst introduced by Lichtenstein (1950). However, the term seems to be inaccurate, since the lesion is neither a true aneurysm nor a cyst. Several hypotheses on the pathogenesis of aneurysmal bone cyst have been proposed. These include: (1) alterations of local osseous hemodynamics with elevated venous pressure (Lichtenstein 1950); (2) predisposing factors such as trauma (Levy et al. 1975); (3) local thrombosis of veins and arterovenous malformations (Bernier and Bhasker 1958); (4) vascular alterations due to a preexisting bony disorder (i.e., angioma, chondroblastoma, chondromyxoid fibroma, fibrosarcoma, fibrous dysplasia, giant cell tumor, hemangioendo-thelioma, histiocytoma, nonossifying fibroma, non-osteogenic fibroma, osteoblastoma, osteoclastoma, a
Fig. 8.6a,b. Ossifying fibroma. Gd-DTPA SE T1 on coronal (a) and sagittal (b) plane. Huge, brightly enhancing ethmoido-maxillary mass encroaching both the nasal septum (black arrowhead) and the anterior cranial fossa floor (white arrow). Medial orbital wall is laterally displaced (black arrow) but not invaded
Fig. 8.6a,b. Ossifying fibroma. Gd-DTPA SE T1 on coronal (a) and sagittal (b) plane. Huge, brightly enhancing ethmoido-maxillary mass encroaching both the nasal septum (black arrowhead) and the anterior cranial fossa floor (white arrow). Medial orbital wall is laterally displaced (black arrow) but not invaded b a osteosarcoma, unicameral bone cyst). (CitarDi et al. 1996; KransDorF and Sweet 1995; Buraczewski and Dabska 1971)
Aneurysmal bone cyst is slightly more frequent in females and develops in about 90% of patients during the first two decades of life (JaFFe and LichtensteiN 1942; CaLLiauw et al. 1985). Most lesions involve long bone metaphyses, vertebrae, and pelvis, whereas the occurrence in the head and neck area is sporadic (2%). The mandible and maxilla are involved in 66% and 33% of cases, respectively, while rarely aneurys-mal bone cyst has been observed in the orbitoethmoid complex (CitarDi et al. 1996; ChateiL et al. 1997).
As described by Buraczewski and Dabska (1971), the development of aneurysmal bone cyst follows three different stages: the initial phase (I stage), which is characterized by osteolysis without peculiar findings; the growth phase (II stage), showing a rapid increase in size with osseous erosion and enlargement of involved bone associated with formation of a shell around the central part of the lesion; the stabilization phase (III stage), with a fully developed radiological pattern.
Histologically, aneurysmal bone cyst is classified into two variants. The classic form, which is the most common (about 95% of cases), is composed of blood-filled clefts among bony trabeculae associated with osteoid tissue in the stromal matrix (Kershisnik and Batsakis 1994). The solid form, which affects 5% of patients, is characterized by osteoid production, fibroblastic proliferation, and degenerated calcifying fibromyxoid elements (Sankerkin et al. 1983).
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