Bone Scans : Mechanisms and Interpretation in Selected Diseases

1. Bone Scans : Mechanisms and Interpretation in Selected Diseases Original presentation : Dr M. Levin Modified for the webpage : Dr M. Levin Contact e-mail for webmasters : webadmin@ich.uct.ac.za Target audience : Registrars

2. Bone Scans : Mechanisms and Interpretation in Selected Diseases The following talk was presented at a continuing education forum at the UCT’s department of Paediatrics in May 2000 by Dr M. Levin. Apart from this one, all slides with a black background were used in the original presentation. Slides with a white background contain a selection of explanatory notes for the following slide.

3. Radio-isotope bone scans have been used in this hospital since the opening of the nuclear medicine department in 1978. They are an extremely useful tool used in the delineation of the site and probable cause of many abnormalities involving bone. From Jan – April 2000, 281 scans were performed, of these 46 (17%) were bone scans - it is an important and frequent investigation in our department. These very clear pictures show the bony anatomy nicely. The abnormal area is the hot spot in the shoulder identified by arrows. On the anterior view it is seen in the left shoulder, but on the posterior view it can be more precisely localised to the scapular bone. Use the mouse/page down to point to the scapula.

4. Bone Scans : Mechanisms and Interpretation in Selected Diseases • 281 scans Jan-April • 113 : 40 % DMSA • 60 : 21 % GOR • 46 : 17 % Bone • 33 : 9 % Mag 3 • 29 : 10 % other

5. The following slides discuss some of the physiology and patho-physiology of abnormal bone scans, and stress the point that scans are most useful in identifying the site and number of abnormalities. In some cases, with appropriate history and clinical examination, they can suggest the probable aetiology. In the 1920’s, the effects of the ingestion of radioactive salts was noted on painters of luminous watch dials. It was discovered that the activity was concentrated in bone, and this led to the use of isotopes of phosphate, fluorine, calcium and strontium in early bone scans. This picture is a normal whole body scan taken at 2 1/2 hours after radioisotope injection.

6. Frequent procedure in nuclear medicine. • Identifies abnormal regions in the skeleton where vascularity or osteogenesis impaired • Highly sensitive : detects pathophysiologic rather than morphologic abnormalities

7. Nowadays Technetium 99m bound to phosphates (either tri or di-phosphates) is used as the isotope of choice and referred to as Technetium 99m:MDP. Other substances that can be used but I will only mention in passing are gallium, thallium, indium labelled leucocytes, technetium labelled leucocytes and polyclonal immunoglobulins labelled with technetium.

8. Bone Scans : Principles • Tc 99 bound to phosphate taken to bone by blood, extracted and reacts at the surface of active bone formation. Incorporated on the surface of hydroxyapatite crystals. • Less dependent on calcium content than x-rays that require a 30 - 50 % change. • Factors influencing the uptake of Tc 99 are • Blood flow • Extraction efficiency

9. The major factor affecting uptake of technetium is the amount of blood reaching the area. Flow can be increased through the hyperaemia of infection leading to a hot – spot such as that seen on the scapula of the child in the first image. Blood flow may be decreased by infection as well, and it is useful to elaborate the reasons for this as it has an important impact on the diagnosis of the cause and severity of these so-called cold abnormalities. Blood flow may be reduced by vasospasm or the development of microthrombi in the arteries leading to the abnormal area.In addition, oedema, and necrosis of tissues, may cause accumulation of fluid under pressure in a limited space – for example a bone, joint or tissue compartment. This increased pressure prevents further perfusion of the area leading to more necrosis and rapid deterioration.. Cold areas indicate a serious pathology – and have been proven to correlate with more severe illness, higher morbidity and mortality, and longer hospital stays. If they are seen within a bone or a joint they are an indication for immediate surgery. Increased or decreased vascularity per-se may also have an effect on blood flow, increased in Pagets disease and the highly vascular osteoid osteoma, and decreased in Perthes.

10. Alterations in Blood Flow • Increased blood flow infection • Decreased blood flow infection reduced by microthrombi, vasospasm, oedema and necrosis of bone with intramedullary abscess formation and increased pressure. • Increased vascularity Paget’s • Decreased vascularity early Perthe’s

11. The other factor affecting technetium uptake is changes in extraction efficiency. Young children have very hot growth plates reflecting the high metabolic rate and incorporation of technetium into these areas. In pathological states, ……increased uptake may be caused by ….

12. Changes in Extraction Efficiency • Physiological in growth plates, active areas • Binding to exposed collagen • Areas of osteoblastic activity • Bone destruction with osteoclastic activity (tumour invasion etc) may be associated with reactive attempts at bone repair and exaggerated Tc uptake at the site of a lytic lesion

13. Because of the multiple mechanisms of abnormality in bone scans, data provided by bone imaging are not highly lesion specific. The value of the technique is in the detection of the lesion, its site and number of lesions, rather than the determination of the cause. The radiologist may be able to make a diagnosis of a specific cause for the abnormality based on pattern recognition and the clinical details.

14. Bone scans delineate site and number of lesions • Data not lesion specific either +ve or -ve difficult to identify exact cause of an abnormality from the scan alone. • Clinical details and pattern recognition allow accurate diagnosis

15. The scan is done in three parts. Dynamic images may be obtained but are often omitted due to their limited use. The Blood pool, taken 1 minute post injection, mostly reflects changes in capillary permeability and is useful for seeing highly vascular areas. The late static image reflects bone uptake, and is taken at 2 – 4 hours to allow the kidneys to excrete excess, unbound technetium polyphosphate and thus allow the best target to background ratio.

16. Technique : 3 Phase Study • Flow phase every 3 secs for 30 secs • “Blood pool” 1 minute post injection reflects body perfusion & changes in capillary permeability • Static image 1.5 - 4 hours later bone uptake maximal at 2 hours urine excretion of excess Tc:MDP

17. Blood pool Static image Whole Body Images

18. Technique : Different Views • Whole body survey takes 7-8 minutes • Supplementary images of areas of interest better positioning • “Pinhole images” For magnification and better detail • SPECT better contrast of structures

19. This slide shows a pinhole image of two hips. The one on your right is a normal hip, the one on the left shows an area of decreased activity in a child with healing perthes disease. Use the mouse/page down to point to the lesion

20. Pinhole Image :

21. Applications for Bone Scans • Bone, joint and soft tissue infection • Vascular disorders • Trauma • Primary bone tumours • Metastatic disease • Extra-osseous activity

22. Bone and soft tissue infection The use of bone scans in the diagnosis of osteomyelitis was established in 1975. This year also saw the introduction of the early blood pool or tissue phase images to aid in the diagnosis. This slide shows an area of soft tissue involvement with a severe cellulitis, a cold femoral shaft, and a completely cold femoral head. On the other side the femoral head is also completely cold, indicating bilateral severe arthritis. Use the mouse/page down to point to the lesions in turn

23. Infection • Bone scans first used in 1975 for the diagnosis of bone skin and soft tissue infection. • The same year saw the introduction of blood pool or tissue phase images.

24. Bone scans are considerably superior to x-rays in the early diagnosis of osteomyelitis. Scans may be abnormal very early and are usually abnormal within 2 days of the onset of symptoms. …... Alternatively other radiopharmaceuticals such as gallium or labelled leucocytes may be used.

25. Infection • Bone scans may be abnormal within 12 hours after the first symptoms • X-rays take 10 - 14 days to show osteolysis, periostial reaction or calcification • Sensitivity 90 - 98 % but less in neonates • Negative bone scans may be repeated after 2 days if clinical suspicion persists

26. This slide shows increased soft tissue uptake, and a totally cold tibia. • Use the mouse/page down to point to the lesions in turn

27. Infection • Cold areas indicate more severe or aggressive disease with longer hospital stays and worse prognosis. • Cold areas are an indication for urgent surgery.

28. The usual image of septic arthritis is of increased uptake uniform over the whole joint, and limited to the joint. Comparison with the contralateral joint is essential

29. Infection : Septic Arthritis • Increased or decreased uptake uniform over the whole joint. • Comparison of contralateral asymptomatic joint in same position is essential.

30. In the hip, the capsule inserts on the area between the trochanter and the femoral head, and therefore increased pressure of a joint effusion within the capsule may cause a cold femoral head. This necessitated immediate decompression to prevent avascular necrosis. On the other side, the hip is not normal either. There is increased uptake in the femoral head and the acetabulum. The neck and trochanter are normal, however. This is not an arthritis, it is not in the entire joint capsule. It is an osteitis of the femoral head and / or the acetabulum. Use the mouse/page down to point to the lesions in turn

31. Infection : Septic Arthritis • Less uptake and cold femoral head due to high pressure of a joint effusion. • Decompression needed to prevent AVN.

32. Perthe’s Disease • The cause of an “irritable” or painful hip is difficult to diagnose accurately • Perthe’s disease is common and has severe sequelae if missed • Bone scans are 98 % sensitive & 95 % specific • Staging of Perthe’s is possible early • Absence of uptake in the lateral aspect of the femoral head, corresponding to the area of necrosis in the proximal femoral epiphysis

33. Perthe’s Disease • Associated synovitis with increased uptake in acetabulum • Revascularisation and healing seen (next picture) prior to x-ray changes of new bone formation

34. These pinhole images show a severe Perthes on the top left, progressing through the stages of healing to a joint with only a slight decrease of uptake in the superior lateral portion of the femoral head, and minimal disruption of the smooth, round surface of the head.

35. 27/ 7 / 92 4 / 2 / 93 27 / 4 / 93 27 / 9 / 93

36. Fractures Within hours of a fracture, bone scans of the area can be abnormal. At two weeks, uptake is intense at the fracture area and then decreases gradually over the next 8 weeks. NAI bone injuries in children assume unique characteristic patterns because of the nature of the growing skeleton and the characteristic types of injuries. In addition extra-osseous abnormalities may be seen.

37. Trauma : Non Accidental Injury • Within hours of a fracture bone scans of the area can be abnormal • Lesions tend to be multiple and symmetric • May be in different stages of healing • Characteristic sites : rib “grasp” injuries • Characteristic types : twisting, corner #s • Extra-osseous abnormalities : cerebral and renal infarction and local haematomas

38. These striking images, taken from the back, show grasp injuries of the ribs, and increased uptake in the left elbow region and the pelvis. This child had multiple other abnormalities. The bone scan is more sensitive to periostial injury that initial x-ray skeletal surveys. There are however limitations to the bone scan.

39. Non-accidental Injury

40. Non Accidental Injury • Bone scans can not : • determine various stages of healing • detect completely healed fracture • Difficult to : • detect subtle symmetrical abnormalities • detect skull fractures • Localise areas with bone scan, then follow with SXR and areas identified by the scan.

41. The last subject I would like to discuss is the use of bone scans to detect the presence of bony metastases and primary bone tumours. It is an extremely sensitive test, detecting mets not seen on x-rays in >30 % of adults with malignancy, and >35% of children with solid tumours. Neuroblastoma is one of the most common childhood tumours. Detection of metastases significantly alters therapy and prognosis. This picture shows the site of the primary neuroblastoma in the R adrenal area, and metastases in the R shoulder and L distal femoral metaphysis. Use the mouse/page down to point to the lesions in turn: the arrow is the primary, the circles are the mets. Mets can be seen as photobright or photopenic abnormalities. Metaphyseal metastases are common and in the early stages show as subtle blurring of the growth plate and increased intra-articular deposition. Another possible application is the use of bone scans to identify areas for percutaneous bone biopsy which is an effective and safe diagnostic tool.

42. Neuroblastoma • One of the most common malignant tumours in children • Photobright lesions at sites of mets and in about 50 % of primary tumours • Metastases often photopenic.