**13.2 Applications of bone scintigraphy in pediatric populations**

#### **13.2.1 Infections**

Acute osteomyelitis is a common pediatric disease that mostly affects children under 5 years old. It usually is the result of hematogenous spread of infection due to the rich vascular supply of the growing skeleton. Typically, bone scan become positive 24 to 72 hours after the onset of infection, while plain films do not manifest evidence of infection until 3 to 4 weeks after. Therefore, three-phase bone scintigraphy is the most sensitive imaging modality for early diagnosis. The sensitivity of a three-phase bone scan has been estimated as 94% with a specificity of 95% (Shammas, 2009; as cited in Schauwecker, 1992). Ideally, scintigraphic imaging should be obtained before joint aspiration, and a delayed whole-body scan on skeletal phase should be obtained because osteomyelitis in childhood can be multifocal or present with referred pain. In addition, malignant disease such as leukemia

Proper positioning is important in pediatrics particularly in young infants, and although children are smaller, it does not imply that more of a child can be imaged on a single scintigraphic view. In fact, examinations take longer in children and infants because of the requirement of joint-to-joint images for detailed assessment. Although the new gamma camera systems often allow whole-body passes it is often necessary to supplement these images with magnified spot views or even pinhole imaging. Image magnification either with camera zoom, computer magnification, or collimation is essential when performing scintigraphic examinations in children. Magnification is either optical with collimation or electronic. Optical magnification uses either a pinhole or converging collimator, enlarges the image, and improves overall system resolution. Electronic magnification makes the image bigger without altering overall system resolution. The capability for SPECT imaging is essential in pediatric scintigraphy. SPECT allows for improved image contrast and hence improved diagnostic accuracy. It is helpful in localizing and further defining most musculoskeletal abnormalities to include the extremities and is essential when assessing a child with the clinical problem of back pain. Multiple head detector gamma camera systems are becoming more available in pediatric centers. The advantages of these systems include increased resolution and sensitivity and decreased time of examination in a child. Correlative imaging is essential to state of the art practice of pediatric nuclear medicine. Computer multimodality image fusion programs are becoming available and more sophisticated. They allow comparison of different isotope scintigraphic studies or serial studies in the same patient or comparison of scintigraphy with other imaging modalities, such as CT, MR imaging, and PET for better correlation of anatomy and function. New combined gamma camera and CT devices allowing direct anatomic and physiologic correlation are also being manufactured and will have further impact on the care of the

The normal distribution in a pediatric bone scan may differ from adults (Shammas, 2009; as cited in Nadel, 2007). In children there is high physeal and apophyseal uptake due to their rich blood supply and active enchondral ossification. Absence of uptake in nonossified cartilaginous structures should not be mis- taken for avascular necrosis. Regions where this may be of concern in younger children include the femoral capital epiphysis, patella, and navicular bone. Before ossification, the ischiopubic synchondrosis appears as a discontinuity of the inferior pubic ramus. During ossification, increased uptake in ischiopubic synchondroses is a common normal variant and should not be misinterpreted as a

Acute osteomyelitis is a common pediatric disease that mostly affects children under 5 years old. It usually is the result of hematogenous spread of infection due to the rich vascular supply of the growing skeleton. Typically, bone scan become positive 24 to 72 hours after the onset of infection, while plain films do not manifest evidence of infection until 3 to 4 weeks after. Therefore, three-phase bone scintigraphy is the most sensitive imaging modality for early diagnosis. The sensitivity of a three-phase bone scan has been estimated as 94% with a specificity of 95% (Shammas, 2009; as cited in Schauwecker, 1992). Ideally, scintigraphic imaging should be obtained before joint aspiration, and a delayed whole-body scan on skeletal phase should be obtained because osteomyelitis in childhood can be multifocal or present with referred pain. In addition, malignant disease such as leukemia

pediatric patient.

**13.2.1 Infections** 

pathological lesion (Shammas, 2009).

**13.2 Applications of bone scintigraphy in pediatric populations** 

and sarcoma may mimic acute osteomyelitis (Shammas, 2009; as cited in Connolly et al., 2007; Ma et al., 2007). All three phases of the bone scan show focally high uptake in the affected bone. Occasionally, the affected bone in children shows low uptake or a photopenic defect (cold osteomyelitis) (Shammas, 2009; as cited in Pennington, 1999). This is most likely due to reduced tracer delivery by increased intraosseous pressure from inflammation, oedema, and joint effusion (Shammas, 2009). Cellulitis may be differentiated from osteomyelitis because the former typically demonstrates diffuse increased activity in the soft tissues on the first two phases, without focal osseous abnormality on the third phase (Shammas, 2009; as cited in Wegener & Alavi, 1991). Although chronic recurrent multifocal osteomyelitis (CRMO) and acute osteomyelitis share a common histopathologic feature, namely chronic inflammation, they are different in important ways (Nadel & Stilwell, 2001). CRMO occurs most frequently in the latter half of the first decade and the first half of the second decade of life, and it is more common in girls, differently from acute osteomyelitis that occurs in children under 5 years old (Shammas, 2009). A predisposing cause is not found for CRMO in contrast to conventional osteomyelitis (Nadel & Stilwell, 2001). Bone scintigraphy is helpful in identifying the multifocal bone lesions and characteristically displays high uptake in both symptomatic and asymptomatic lesions (Shammas, 2009, as cited in Connolly, 2007). Other infection typical of children under 3 years of age is septic arthritis. Monoarticular involvement is the most common pattern. The more affected joints are the knees and the hips. As in the osteomyelitis, there is an increased uptake on all three phases of three-phase bone scan, but in septic arthritis there is a symmetric uptake in both sides of the joint (Diaz& De Haro, 2005). Transient synovitis is the most common condition that mimics septic arthritis. In this case, three-phase bone scan may be normal or may show diffuse increased activity on the first two phases. Delayed images may displa periarticular increased activity in the affected joint (Shammas, 2009).
