**13.2.7 Primary bone tumors in childhood**

128 12 Chapters on Nuclear Medicine

assessing the vascularity of the femoral head. In the absence of avascular necrosis, the bone scan findings in slipped capital femoral epiphysis are nonspecific and consist of mildly increased activity with widening and blurring of the growth plate activity (Shammas, 2009;

Sickle cell disease is the most common hereditary blood disorders. It occurs almost exclusively among black americans and black africans, related with the presence of a mutated form of hemoglobin, hemoglobin S. Bone and joint problems are the most common manifestations. Distinguishing sickle cell crisis with possible bone marrow infartion from osteomyelitis is a challenge (Shammas, 2009; as cited in Connolly et al., 2007). Bone marrow scan with 99mTc-sulfur colloid plus conventional bone scan may be used in the evaluation of sickle cell disease, but it should be done within the first 7 days after the pain onset to be helpful in the differential diagnosis (Shammas, 2009). If the bone marrow scan is abnormal at the site of pain, followed by normal or decreased uptake on conventional bone scan, infarction is the likely diagnosis. Increased uptake in blood pool and delayed images on conventional bone scan is more suggestive of osteomyelitis (Shammas, 2009; as cited in

Reflex sympathetic dystrophy has also been described elsewhere in this chapter. The typical findings on three-phase bone scan are hyperemia on the first two phases with intense periarticular activity in the affected extremity. In children, a cold variant has been reported, which is characterized by decreased activity in the three phases of the scintigraphy in the affected limb, compared with the nonaffected limb (Shammas, 2009; as cited in Nadel, 2007).

The occult fracture more common in children is the Toddler's fracture, which is a spiral or oblique fracture that can occur from pelvis to feet but mostly involves the tibia (Shammas, 2009). Radiographic findings are often subtle and fractures may not be apparent, for that reason bone scan is a valuable tool for detecting this injury. Scintigraphy shows diffuse increased uptake in the tibial diaphysis or the bone affected. A linear or spiral pattern of high uptake may be seen in some children (Shammas, 2009; as cited in Connolly et al., 2006;

Among stress fractures, spondylolysis is the more important in children with back pain, which represent a stress fracture of the pars interarticularis of the vertebra, commonly in the lower lumbar spine secondary to repetitive minor trauma such as hyperextension (Shammas, 2009). Clinical signs and symptons and radiographies are normally used for the diagnosis. A bone scan or a MRI may be necessary to determine if the spondylolysis is active or inactive. Bone scintigraphy shows little or no abnormality on blood pool images, but it typically demonstrates focally high uptake in the region of the pars interarticularis on delayed images. SPECT imaging is more sensitive than planar studies and detects abnormalities in about a third of individuals with normal planar examinations and so, it is recommended in the evaluation of low back pain in young athletes (Shammas, 2009; as cited

Scintigraphy has also an important role to provide a quick assessment for defining and characterizing the extent and severity of trauma in the setting of child abuse, complementary

as cited in Connolly et al., 2006, 2007).

**13.2.5 Reflex sympathetic dystrophy** 

**13.2.4 Sickle cell disease** 

Gilday, 2003).

**13.2.6 Fractures** 

Gilday 2003).

in Sty, 1993).

Benign bone tumors are by far the most common type of tumors that grow within the skeleton. Nonossifying fibromas, osteochondromas and simple bone cysts are the types most often found in children and teenagers. Children between the ages of 6 and 12 are the most likely to develop benign bone tumors, although the tumors sometimes show up in children as young as age 2. Exostosis tumors are slightly more common in boys than girls. Nonossifying fibroma usually is in the actively growing sections of long bones such as the thighbone (femur). Exostosis (osteochondroma) contains both bone and cartilage and usually grows in the thighbone, the shinbone (tibia) or the bone in the upper arm (humerus). Unicameral (simple) bone cysts are holes in the bone that fill with fluid and tissue. They usually occur in the bone in the upper arm or in the upper part of the thighbone. In some cases, a benign bone tumor can cause problems while it grows. It can weaken the child's bone and make it more likely that the bone will break. Tumors also can press on nerves and cause pain. In cases like these, surgery may be necessary. Malignant primary bone tumors make up 5% of childhood malignancies, and osteosarcoma is the most commonly isolated malignant bone tumor in children, followed by Ewing's sarcoma. These bone neoplasms usually begin during childhood and adolescence, when bones are growing quickly and they often are taking part in sports and other physical activities. Langerhans cell histiocytosis is also more common in the pediatric population. A smaller number of patients have other diagnosis such as malignant fibrous histiocytoma, angiosarcoma and chondrosarcoma, but these conditions are very rare in paediatric population. The use of nuclear medicine techniques in the diagnosis, staging and monitoring of the different bone tumors has been detailed in a previous section of this chapter. FDG-PET has become to be one of the best tools for the baseline evaluation and follow-up, although some benign bone lesions may show high 18F-FDG accumulation, equivalent to osteosarcomas. Despite this, 18F-FDG-PET has a high specificity for excluding malignant bone tumors (Cook et al., 2010). FDG- PET has been shown to help determine the presence and extent of sarcomas and even may allow the noninvasive estimation of the histologic grade of some tumors, although the biopsy remains necessary. This technique allows targeted biopsies, which can reduce the likelihood of underestimation of tumor grade and inadequate therapy. Furthermore, 18F-FDG-PET is useful in the pediatric population for detection of skip metastases in cases of equivocal MRI findings (Even-Sapir, 2007).
