in Planar and Hybrid Bone and Joint Imaging

Fig. 1

Patient for breast cancer staging. Besides multiple metastases (scapula, pelvis, spine) the increased uptake in the distal upper extremity is caused by intraarterial radiotracer injection

Paravasation of radiotracer at the injection site may lead to hot spots that may mask pathologic uptake and might lead to “sentinel nodes” in the axilla (Fig. 2).

Fig. 2

Patient for prostate cancer staging. No metastases visible. Three focal uptakes in the right axilla representing “sentinel nodes” due to paravasation of radiotracer at the right elbow injection site

Injection through central venous catheter might lead to retention of activity in the plastic tube. Patient movement can lead to false positive and false negative findings by summation or masking of tracer uptake (Fig. 3).

Fig. 3

Posterior planar bone scan in a child for sarcoma staging. Threefold visibility of the right arm due to patient movement

Contamination with urine is a relative common cause of uptake in the pelvis and can be avoided by removal of underwear (Fig. 4). If contamination is suspected cleaning and repetition of spot images or SPECT/CT can be obtained to avoid misinterpretation.

Fig. 4

Patient for prostate cancer staging with focal uptake in the left pelvis. Spot image after removal of underwear confirms urine contamination and excludes metastasis

Normal Variants and Benign Pitfall Lesions

Focal uptake in the skull in tumor staging bone scans is often visible and might represent benign incidentally detected lesions like meningioma, osteoma or fibrous dysplasia [1] (Fig. 5).

Fig. 5

Patient for prostate cancer staging with incidental uptake in two skull lesions on planar images. SPECT/CT shows typical appearance of fibrous dysplasia (right side) and hemangioma (left side)

Increased uptake in the frontal skull is often related to hyperostosis frontalis interna [2]. The typical appearance of these skull lesions in diagnostic CT enables to rule out metastasis in most cases by performing a dedicated SPECT/CT. Increased focal uptake in the jaw is regularly seen on bone scans and FDG PET/CT and most likely represents inflammatory lesions with dental origin or healing processes after dental interventions. Typical sternal midline longitudinal uptake in bone scan and FDG PET/CT is related to patients after sternotomy due to cardiothoracic surgery. Some uptake in the manubriosternal synchondrosis ist regularly seen in asymptomatic patients and should not be misinterpreted for inflammation or metastasis [3]. The majority of rib lesions on bone scans and to a lesser extent in FDG PET/CT is not caused by metastases but by trauma or benign lesions like enchondroma or fibrous dysplasia. If the clinical history and pattern of uptake is unspecific SPECT/CT can add important information by showing fractures, osteolysis or osteoblastic rib lesions.

While most tracers are excreted through the renal system, pathologies in the urinary tract and urine contamination can lead to various pitfalls like bladder diverticulum, urinoma and renal concrements [4] (Fig. 6).

Fig. 6

Patient for prostate cancer staging with focal increased uptake in the right pelvis. Lateral spot image shows that the uptake is probably not in the bone. SPECT/CT comfirms uptake in a distal ureter concrement

In children uptake in the physeal and apophyseal growth centers of the long bones is a normal finding in bone scans. Physiologic uptake in the ischiopubic synchondrosis in children should not be mistaken for osteomyelitis, tumor or trauma. Additional x-rays or MR—in doubtful cases—can help to provide the correct diagnosis. Increased uptake at the insertion or origin side of tendons like at ischiac bone (ischiocrural muscle), pubic bone and femur (adductor muscles), ribs (pectoralis muscle), humeral head (deltoid muscle), greater trochanter (abductor muscles), greater tuberculum (supraspinatus muscle) might represent physiologic uptake or enthesopathy and should not be mistaken for metastases [5]. Incidental uptake in the spine in tumor patients is regularly seen and often related to degenerative lesions, especially in the cervical and lumbar spine. If the scintigraphic pattern is unspecific additional imaging with conventional x-rays or SPECT/CT are able to clarify the lesions in the majority of cases [6, 7].

Regarding staging of tumor patients with bone scintigraphy one should be aware of the pitfall, that aggressive osteolytic bone metastases—like in breast cancer—might be invisible due to the absence of osteoblastic tumor components (Fig. 7).

Fig. 7

Patient with breast cancer and normal bone scan. FDG PET/CT shows pathologic FDG uptake in an osteolytic bone metastasis in the right iliac bone and multiple active lymph node metastases in the left axilla

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