Radiographs are initially performed for detection and gross characterization of bone tumors. For most aggressive lesions, MR is the next step for more detailed evaluation. The relationship between the tumor and nearby joints and growth plates, as well as any soft tissue extension and relationship to neurovascular bundles, are best shown on MR. Intravenous gadolinium is administered to distinguish solid components from cysts, and tumor from reactive marrow edema. CT is helpful when trying to characterize tumoral calcification or periosteal elevation, particularly for benign lesions. Technetium-99m bone scintigraphy may be used to distinguish monostotic versus polyostotic disease, such as with fibrous dysplasia, or “skip” lesions in osteosarcoma.

Osteochondroma, or exostosis, is the most common benign bone tumor. It represents a protuberance from the parent bone with both cortical and medullary continuity and is lined by a cap of hyaline cartilage. The exostosis develops as a result of displaced physeal cartilage that herniates through the periosteum. The most common sites are the distal femur, proximal femur, and proximal tibia (areas of greatest bone growth). Osteochondromas may be solitary or multiple. Multiple hereditary exostosis (MHE) is an autosomal dominant condition in which patients often have significant growth disturbances. While most osteochondromas are asymptomatic, they may present with pain due to irritation of an overlying bursa or neurovascular bundle. Exostoses typically stop growing when the child is skeletally mature. Malignant transformation into chondrosarcoma is very rare in children, though increased rates are seen in patients with MHE or when the cartilage cap is thicker than 1.5 to 2 cm. Surgical excision is performed if the exostosis remains symptomatic and grows after skeletal maturity, or if malignant transformation is suspected.”

On imaging, osteochondromas may be pedunculated or sessile and demonstrate corticomedullary continuity with the parent
bone (Figs. 29.1 and 29.2). They most often arise from long bone metaphyses and are directed away from the joint. MR is helpful for identifying pathologic fractures and any overlying soft tissue abnormalities.¹ On T2W or cartilage-sensitive sequences, the cartilaginous cap is normally a thin crescentic, high-signal structure (Fig. 29.3).

Enchondroma is another common benign bone tumor in both children and adults. This tumor is composed of cartilage cells from the nearby growth plate. Enchondromas account for 80% of primary hand tumors in children, and are most common within the hands and feet along with the metaphysis of any long bone. Ollier disease (enchondromatosis) features numerous expansile cartilaginous tumors with resultant skeletal deformity. Maffucci syndrome combines enchondromatosis with soft tissue vascular malformations. On radiographs, enchondromas are ovoid or lobular lucent lesions with thin sclerotic margins (Figs. 29.4, 29.5 and 29.6). The medullary cavity may be expanded asymmetrically with endosteal scalloping. Characteristic chondroid calcifications are “rings and arcs,” or dense and punctate (“popcorn”), on radiographs and CT (Figs. 29.4, 29.5 and 29.6). On MR, enchondromas demonstrate high T2W signal except for low-signal calcifications, and variable enhancement (Fig. 29.6B). Enchondromas typically do not need follow-up imaging or biopsy for confirmation.¹

Chondroblastoma is a rare cartilaginous tumor best identified by its proclivity for the epiphysis or apophysis (an epiphysis equivalent). The proximal humerus and tibia are the most common locations.
These tumors often present with pain and impaired function of the adjacent joint. Radiographs and CT will show a lobular lucent lesion with sclerotic margins and chondroid calcification, similar to an enchondroma (Fig. 29.7A, B). On MR, there is often surrounding marrow edema and an associated joint effusion (Fig. 29.7C). These peritumoral inflammatory changes are absent with enchondromas. Chondroblastoma is treated with curettage and bone grafting, with a 20% likelihood of local recurrence.^{1,8, 9 and 10}

SBC, also referred to as solitary bone cyst or unicameral bone cyst, is a fluid- or blood-filled cavity lined by a thin membrane of connective tissue. The etiology of SBC has not been fully clarified, though preexisting vascular anomaly and defect in endochondral bone formation have been theorized. They are two to three times more common in boys than girls. These cysts generally arise in the metaphyses of large tubular bones. The most common locations are the proximal humerus (50%) and proximal femur. The calcaneus is another uncommon, but well-documented, site for cysts. SBC is the most common cause of pathologic fracture in children, and the majority of these lesions present in this way.^1,11

Radiographically, an SBC appears as an ovoid lucency with thin sclerotic margins, typically located in the central metaphysis of a long bone (Fig. 29.8). The long axis of the cyst is parallel to that of the bone. The “fallen fragment” sign is pathognomonic for SBC. When a pathologic fracture occurs, the fragments layer dependently within the cyst. After a fracture heals, the SBC may exhibit septations and sclerosis. CT and MR are generally not needed for further characterization of SBC.^1,11

Treatment for simple cysts is curettage and bone grafting.¹¹ After treatment, the cyst often has a more complex appearance with septations and a mixed lucent/sclerotic pattern. Up to onehalf of SBCs recur following treatment, so routine follow-up radiography is generally performed.¹ Recurrence is evident when the lesion becomes more lucent rather than gradually denser.

Aneurysmal bone cyst (ABC) is a blood-filled cavity within a distended segment of bone. Though etiology is unclear, it is theorized that an ABC is the result of hemorrhage from an underlying
bone tumor or vascular malformation. In cases where a pre-existing lesion can be identified, the most common of these is giant cell tumor.¹² ABCs are most common in adolescents and young adults and slightly more common in girls. They usually arise in long bone metaphyses and the posterior elements of the spine. Pain and swelling are typical presenting symptoms. As with SBC, treatment for ABC is curettage and bone grafting.^1,12,13

On imaging, ABCs are expansile lucent lesions with thin or imperceptible (“blown-out”) cortex (Fig. 29.9A). This multiloculated appearance has also been referred to as “soap bubble.” Fluid-fluid levels are seen on either CT or MR (Fig. 29.9B). While fluid-fluid levels are typical of ABC, they are not pathognomonic, and a variety of bone lesions may show them. These cysts generally show thin septal and peripheral enhancement. Solid nodular enhancement may occasionally be observed with ABC, though suspicion should be raised for telangiectatic osteosarcoma in this setting. Nodular components should be highlighted to the surgeon for possible biopsy targets.^{12, 13, 14, 15 and 16}

Fibroxanthomas are very common fibrous lesions centered within the cortex. Since they are seen in up to 40% of children, they may be better characterized as developmental variants rather than benign neoplasms. The term fibroxanthoma incorporates both nonossifying fibroma (NOF, >2 cm) and fibrous cortical defect (FCD, <2 cm). The majority of fibroxanthomas arise from the metaphyses of long bones, and 80% to 90% of them occur around the knee. They are usually asymptomatic and discovered incidentally. Radiographs are diagnostic for this condition. Fibroxanthomas
appear as cortical-based ovoid lucencies with smooth sclerotic margins (Fig. 29.10). They tend to bulge toward the medullary cavity, and the surrounding cortex is intact. As fibroxanthomas involute, they become more sclerotic and less apparent on imaging. Treatment with curettage and bone graft is only indicated for larger lesions at risk for pathologic fracture.^{7,17, 18, 19 and 20}

Fibrous dysplasia is a nonheritable disorder in which failure of normal bone maturation leads to replacement of medullary cavity by immature fibro-osseous stroma. While not a true neoplasm, the condition often mimics bone tumors and cysts on all imaging modalities. About 80% of patients have monostotic disease. The most common sites of involvement are long bones, ribs, craniofacial bones, and the pelvis. When polyostotic disease occurs, it usually afflicts one extremity or one side of the body and may be syndromic. Two to three percent of patients with fibrous dysplasia have associated endocrinopathies from hypothalamic dysfunction. McCune-Albright syndrome is a rare disorder that affects girls and comprises polyostotic fibrous dysplasia, cutaneous café au lait spots, and precocious puberty. There is no gender predilection for fibrous dysplasia. Patients may present with pain, deformity, or pathologic fracture.^1,20,

Stay updated, free articles. Join our Telegram channel

Join