Benign Bone Tumors David L. G i l d a y a n d Judith M. Ash
There is little information in the literature concerning the role of bone scanning in benign bone neoplasms except for sporadic reports. Since the advent of 99mTcpolyphosphate, bone imaging has proven feasible and useful in locating the cause of bone pain, such as in osteoid osteomas, which are nat always radiologically apparent, and in evaluating whether or not a radiologic lesion is indeed benign and solitary. Blood-poe[ images are particularly important in neoplastic disease, since the absence of hyperemla in the immediate postinjection period favors the diagnosis of a benign neoplasm, as does low-grade uptake on the delayed study. The scan, including pinhole magnification images, is especially valuable in diagnosing lesions in the spine and pelvis,
which are poorly seen radiologically. We have studied various types of benign bone tumors, including simple and aneurysmal bone cysts, fibrous cortical defects, and nonossifying fibromas, all of which had minimal or no increased uptake of the radiapharmaceutical, unless traumatized. Although osteochondromas and enchondramas shewed varied accumulation of activity, the scan was useful in differentiating these from sarcomatous lesions. All osteoid osteomas demonstrated marked activity, and could be accurately located preoperatively, as could the extent of fibrous dysplasia. The bone scan in the reticuloses also showed abnormal accumulation of activity, and aided in arriving at the prognosis and treatment of histiocytic bone lesions.
p
,RIOR TO THE INTRODUCTION of 99~Tc-polyphosphate,t there were very few data available on bone scanning in benign bone neoplasia due to the requirement that 8SSr be used only in patients with known malignancy, z In those few centers able to obtain 18F, investigation of benign disease was also possible. There have been no extensive reports in the literature of benign bone neoplasms, and the information available is derived from sporadic reports included in longer studies. 3-5 There appear to be two basic indications for performing bone scans in cases of potential benign bone neoplasms. The first is to locate a neoplasm that is causing bone pain, e.g., osteoid osteoma. The second indication is to help decide whether an obvious radiologic lesion is benign or malignant. To assist in the evaluation of these entities, we have found that in most cases, immediate postinjection ("blood-pool") images with the 99mTc-labeled phosphates are valuable in determining the degree of hyperemia of the lesion compared with the ipsilateral normal side. This is especially important in lucent bone lesions, since malignant neoplasms tend to be quite hyperemic, whereas the vast majority of benign ones are not. Adequate evaluation of those neoplasms that are small and difficult to locate radiologically such as osteoid osteomas requires multiple views of the area with From the Division of Nuclear Medicine. Hospitalfor Sick Children, Toronto, Ontario. Canada. David L. Gilday.B. Eng., M.D., F.R.C.P.(C): Head, 19ivision of Nuclear Medicine. ttospitalfor Sick Children, Toronto, Ontario, Canada. Judith M. Ash, B.A.. M.D.. F.R.C.P.(C): Radiologist, Di~Ysionof Nuclear Medicine, Hospitalfor Sick Children, Toronto. Ontario, Canada. Reprint requests should be addressed to David L. Gilday. M.D.. Division of Nuclear Medicine, Hospitalfor Sick Children. 555 University A re.. Toronto. Ontario. Canada. 9 1976 by Grune &Stratton. Inc. Seminars in Nuclear Medicine, Vol. 6, No. 1 (January), 1976
33
Table 1. Osteoid Osteomas
Spine Long bones Femoral neck Talus Skull
Totol
Scan +
X-roy +
4* .5 7 2 1
4 5 7 2 1
2 4t 6'1" 1t 1
*One not operated on; being followed clinically. 1"Subsequentlydelineated by special radiography.
,dr t R 6
L.
Fig. !. Intertrochanterlc osteoid osteoma. (A) Pinhole view of right hip showing focal " h o t " spot near lesser trochanter. (B) Normal left hip. (C) Radiograph showing questionable abnormality prior to scan. (D) Appropriate view, after scan pinpointed the abnormality, demonstrates'the lesion. 34
BENIGN TUMORS
35
:.~.. - ". !'r
9 ..": :. "~r
.2~'.
." ::.2.-.
..,..
9 "., " "" "~.-'.'-"..i"' " : .. :.""'.~C ~:.' : . 9 :"L-,~;'L.-
.? ",_~....
- ....~.,..:-~... L~" ":-"
--" "-:
I_ ~ ~ : : ~-*.. ~ ....
9
.
R
A
Fig. 2. Spinal osteoid osteoma. (A) Posterior scan of lumbar spine and pelvis, showing obvious focal accumulation of activity on the right at L-5-5-1. (B) This was only recognized on additional radiographs done afterwards, as an area of sclerosis involving the right ala of 5-1 and the inferior articular facet and pedicle of L-5.
a high information density. We collect 2000-3000 counts per square centimeter over the shaft of the bone in the metaphyseal region, using a 25,000-hole collimator. Magnification views using either a converging collimator or a pinhole collimator for maximum enlargement can frequently help delineate the exact location and extent of the abnormality. OSTEOID OSTEOMA
This is the largest group of benign bone neoplasms that we have encountered. To date, we have diagnosed 19 osteoid osteomas, 15 of which have been confirmed surgically and four are being followed clinically (Table I). The most c o m m o n indication for studying this group was to determine the cause o f bone
36
GILDAY AND ASH
P
O P A
13
Vx
f
C
Fig. 3. Osteoma of left occiput. (A) Bloodpool images demonstrate the vascular nature of the asteoma, which is obvious on the delayed posterior view (B) and the vertex view (C).
pain. Almost invariably, the history was atypical and the diagnosis was in question radiologically. When there was a suspicious radiologic change, confirmation of the presence ofan osteoid osteoma was possible by the bone scan. Even when no radiologic changes were evident, the bone scan detected several osteoid osteomas. Radiologicaily, it is difficult to evaluate osteoid osteomas in certain areas of the body, namely the spine, the femoral neck region, and the small bones of the feet (Table 1). In such instances, the complete nuclear medicine study with high information density, multiple-view bone scans, and pinhole magnification has been necessary in the diagnosis of an osteoid osteoma. Subsequent radiologie tomography, in the appropriate projection, usually confirmed the presence of the osteoid osteoma. In several of our cases, tomography was not positive and the bone scan had to be used to locate the lesion immediately prior to surgery.
BENIGN TUMORS
37
P
13
Fig. 4. Fracture through a simple bone cyst. (A) The tomogram shows a simple bone cyst in the right femoral neck with a questionable linear lucency across its lower portion, but not diagnostic of fracture. (B) The marked uptake in this area on the bone scan confirms that trauma occurred. (C) The pinhole view demonStrates increased uptake around the fracture at the lower portion of the cyst, which can be seen as a relatively cooler area above.
,.JiIdlb~.
"' '~"
"."i C
We have found that it is almost always necessary to do pinhole imaging of the hip region to delineate the exact location of femoral neck or intertrochanteric-region osteoid osteomas (Fig. 1). Quite frequently, the child's severe pain precludes proper positioning for the standard radiographs of the femur. However, once a lesion has been demonstrated by bone scan, it is imperative to
38
GILDAY AND ASH
.
?.,.
R
B
L
ANT
Fig. 5. Nonossifying fibroma. (A) The radiograph shows a lesion in the left tiblal metaphysis diagnosed as a nonossifying flbroma. (B) Bone scan of the knees demonstrates a corresponding minimal increase in activity at the medial aspect of the left tibia when compared with the normal right.
obtain appropriate radiographic views of the area, using sedation and analgesics if necessary. The bone scan is probably least valuable in osteoid osteomas of the long bones, since the radiologic diagnosis is usually definitive. The converse is true in the spine. Not only is it difficult to evaluate this area radiologically, but frequently the children are treated for other causes o f back pain and the investigation for osteoid osteoma is not performed. We have had several such cases, each with a long and complicated history. In two instances, symptoms were present for more than 2 years and each boy had had significant orthopedic and neurosurgical intervention for back pain. In both cases, it was very obvious from the nuclear medicine study that there was an osteoid osteoma present in the spine (Fig. 2). In one case, the additional radiographs subsequently demonstrated a very abnormal superior articular facet of the vertebral body. This was removed with immediate resolution of the patient's symptoms. In the other, tomograms were normal and the patient h a d to have a preoperative localization of the osteoid osteoma by bone scanning. This was successful and enabled the surgeons to find the osteoid osteoma, which was confirmed pathologically.
Fig. 6. Osteogenic sarcoma of femur. (A) Radiograph of the left knee shows cortical destruction with new bone formation and a soft-tissue mass at the latoral femoral condyle. (B) The blood-pool image demonstrates typical marked hyperemia to the entire metaphysis and adjacent soft tissue laterally is more extensive than the radiologic abnormality. (C) There is a corresponding area of avid uptake on the delayed scan, most marked laterally.
o
9
9
r
":,'"
it AN E3P I.'1"
B
C 39
40
GILDAY AND ASH
0
POST
R
A
Fig. 7. Osteochondroma, right tibia. (A) The posterior and (B) right lateral scans demonstrate increased uptake limited to the bony prominence seen in the radiograph (C).
BENIGN TUMORS
41
9
:-'!
...., :v"
9
9
.
9
9
-..:~.:.
.
:. ". ". '.'i.:~-'
"
ANT
;'..~....
, . ,
"~'1". 9. 9
C
.-.
.
C] n
.
R
L.
L
..
D
Fig. 8. Sessile osteochondrema, leh femur. (A and B) Radiographs show cortical thickening and apparent destruction above the medial metaphysis with soft-tissue swelling, thought to be a possible sarcoma. (C) The blood image shows no appreciable hyperemia to this area, and (D) the delayed scan demonslrates only minor increased uptake at the site, making the diagnosis of malignancy very unlikely.
42
GILDAY AND ASH
B~ See legend facing page.
BENIGN TUMORS
43
R
A
L
T C MOPN BF
C
D ANT
L
POST
E Fig. 9. Recurrent fibrous dysplasia. This patien't had a craniectomy for fibrous dysplasia 3 years ago and was scanned for reassessment of progression. Radiographs shown in (A and B) demonstrate the bony abnormalities. These are more cleady delineated by the anterior bloodpool image (C) with increased vascularity over the left hemisphere, middle and anterior cranial fossae. The anterior (D) and left lateral (E) delayed images demonstrate avid uptake in the same areas, with a coo[ defect at the previous craniotomy site.
44
GILDAY AND ASH
Ivory osteomas in the skull are also highly vascular and have the same highly intense concentration of the bone radiopharmaceutical as the osteoid osteoma (Fig. 3). CYSTS
T h e r e are two common types of cysts: the simple cyst and the aneurysmal bone cyst. There does not appear to be any significant difference between these on the bone scan. The usual appearance is either minimal or no increase in radioactivity at the site of the cyst. This is not surprising, since the bone is usually not very active metabolically. The bone scan is mainly valuable in determining whether a radiologically lucent lesion is a benign cyst. In our experience the cyst is not " h o t " unless it is traumatized. When a cyst is fractured, the radiographs may be normal and even the tomographic evaluation of the cyst can be equivocal, whereas the bone scan is extremely sensitive in determining whether or not a fracture has occurred (Fig. 4). Cortical defects in bone have a similar appearance to cysts. We have examined seven to date and, in our experience and that of others, the scan is always normal. 6 OTHER NEOPLASMS
Aside from osteoid osteomas, there are few definitely benign bone neoplasms; however, the ones that do occur are most commonly found in children. The n0nossifying fibroma presents as a cystic structure radiologically and usually has a mild increase in radioactivity in the bone scan (Fig. 5). Our experience is similar to reports in the literature that low-grade bone uptake rules out a sarcoma, which typically has an avid accumulation of the radiopharmaceutical and is very hyperemic in the blood-pool images (Fig. 6). However, some benign neoplasms such as osteochondromas, may also show a similar marked increase in activity. 4 The references in the literature concerning the uptake of the radiopharmaceutical by lesions such as enchondromas and osteochondromas have been varied. 7 We have found that osteochondromas generally show very active accumulation o n the bone scan only at the site of bone growth (Fig. 7),. and the diagnosis is usually evident radiologically. However, some sessile osteochondromas and some enchondromas may mimic the appearance of a paraosteal sarcoma on the radiograph. Our experience has shown, however, that these will have a much lower uptake of the radiopharmaceutical than would a malignant lesion (Fig. 8). In some cases, the osteochondromas approach normal bone activityand may not be recognized if the site is unusual. Fibrous dysplasia, on the other hand, has a much more dramatic appearance on the bone scan. It is extremely hyperemic and there is very marked uptake of the radiopharmaceutical on the delayed image. In such instances, it is difficult to differentiate these lesions from a malignant tumor, (long-standing) osteomyelitis, or bone trauma with subperiosteal reaction. The diagnosis is usually made radiologically. The bone scan appears to be most helpful in delineating the extent of the fibrous dysplasia and its recurrence postoperatively (Fig. 9).
BENIGN TUMORS
45
POST
L
POBT
R
R
9
..1 ~. ,,,.~. '
..
9
.'o
.
~,.
,
B
Fig. 10. Eosinophiffc granuloma, right s~apula. (A) The totc!l-body rectilinear scan shows abnormal increased uptake in the region of the right shaulder only. ( " H o t " area in soft tissues of right elbow represents injection site.) (B) On the scintillation camera view, the lesion is localized to the scapula, with uptake mainly around its periphery. (C) Radiograph of the lesion. A second lucent lesion at the distal end of the right femur had a different appearance on the radiograph and showed normal activity on the scan, indicating that it was of a differing nature, i.e., a fibrous cortical defect.
46
GILDAY AND ASH RETICULOSES
There are two basic reticuloses affecting bone. The m o s t c o m m o n one is that o f the histiocytosis X g r o u p , o f which the benign type is the eosinophilic g r a n u l o m a . These have traditionally been g r o u p e d as a reticulosis, although recent t h e o r y indicates that they should be classified separately. T h e b o n e scan can help determine whether or not the histiocytic lesion is solitary, which would m a k e it an eosinophilic g r a n u l o m a or multiple, which w o u l d tend to put it into the m o r e malignant g r o u p o f the histiocytosis X. In o u r experience, the b o n e scan is almost always positive in the eosinophilic g r a n u l o m a (Fig. 10). We have had only one false negative in ten scans.' A n unusual g r o u p o f patients is that with G a u c h e r ' s disease. A l t h o u g h they do not strictly have a benign neoplasm, they do fall into the g r o u p o f patients whose b o n e lesions are often lytic. T h e involved bones d e m o n s t r a t e a vague increase in activity with deformity o f the b o n e itself. In such instances, it is useful to p e r f o r m pinhole imaging o f the hip, since these patients frequently develop avascular necrosis o f the femoral head. REFERENCES
I. Subramanian G, McAfee JG: A new complex of 99mTc for skeletal imaging. Radiology 99:192, 1971 2. Samuels LD: Skeletal scintigraphy in children. Semin Nucl Med 3:89-107, 1973 3. Bell EG, Mahon DF: Bone, in Handmaker tl, Lowenstein JM (eds): Nuclear Medicine in Clinical Pediatrics. New York, The Society of Nuclear Medicine, 1975 4. Bell EG, Subramanian G, Blair RJ, et al:
Bone scanning in pediatrics, in James AE, Wagner tIN Jr, Cooke RE (eds): Pediatric Nuclear Medicine. Philadelphia, Saunders, 1974 5. Gilday DL: Diagnosis of obscure childhood osteoid osteomas with the bone scan. J Nucl Med 15:494, 1.974(abstract) 6. Madj M: Personal communication. 1975 7. Moon NF, Dworkin HJ, LaFleur PD: Clinical use of sodium fluoride-18F in bone photoscanning. JAMA 204:974, 1968
There is little information in the literature concerning the role of bone scanning in benign bone neoplasms except for sporadic reports. Since the advent of 99mTcpolyphosphate, bone imaging has proven feasible and useful in locating the cause of bone pain, such as in osteoid osteomas, which are nat always radiologically apparent, and in evaluating whether or not a radiologic lesion is indeed benign and solitary. Blood-poe[ images are particularly important in neoplastic disease, since the absence of hyperemla in the immediate postinjection period favors the diagnosis of a benign neoplasm, as does low-grade uptake on the delayed study. The scan, including pinhole magnification images, is especially valuable in diagnosing lesions in the spine and pelvis,
which are poorly seen radiologically. We have studied various types of benign bone tumors, including simple and aneurysmal bone cysts, fibrous cortical defects, and nonossifying fibromas, all of which had minimal or no increased uptake of the radiapharmaceutical, unless traumatized. Although osteochondromas and enchondramas shewed varied accumulation of activity, the scan was useful in differentiating these from sarcomatous lesions. All osteoid osteomas demonstrated marked activity, and could be accurately located preoperatively, as could the extent of fibrous dysplasia. The bone scan in the reticuloses also showed abnormal accumulation of activity, and aided in arriving at the prognosis and treatment of histiocytic bone lesions.
p
,RIOR TO THE INTRODUCTION of 99~Tc-polyphosphate,t there were very few data available on bone scanning in benign bone neoplasia due to the requirement that 8SSr be used only in patients with known malignancy, z In those few centers able to obtain 18F, investigation of benign disease was also possible. There have been no extensive reports in the literature of benign bone neoplasms, and the information available is derived from sporadic reports included in longer studies. 3-5 There appear to be two basic indications for performing bone scans in cases of potential benign bone neoplasms. The first is to locate a neoplasm that is causing bone pain, e.g., osteoid osteoma. The second indication is to help decide whether an obvious radiologic lesion is benign or malignant. To assist in the evaluation of these entities, we have found that in most cases, immediate postinjection ("blood-pool") images with the 99mTc-labeled phosphates are valuable in determining the degree of hyperemia of the lesion compared with the ipsilateral normal side. This is especially important in lucent bone lesions, since malignant neoplasms tend to be quite hyperemic, whereas the vast majority of benign ones are not. Adequate evaluation of those neoplasms that are small and difficult to locate radiologically such as osteoid osteomas requires multiple views of the area with From the Division of Nuclear Medicine. Hospitalfor Sick Children, Toronto, Ontario. Canada. David L. Gilday.B. Eng., M.D., F.R.C.P.(C): Head, 19ivision of Nuclear Medicine. ttospitalfor Sick Children, Toronto, Ontario, Canada. Judith M. Ash, B.A.. M.D.. F.R.C.P.(C): Radiologist, Di~Ysionof Nuclear Medicine, Hospitalfor Sick Children, Toronto. Ontario, Canada. Reprint requests should be addressed to David L. Gilday. M.D.. Division of Nuclear Medicine, Hospitalfor Sick Children. 555 University A re.. Toronto. Ontario. Canada. 9 1976 by Grune &Stratton. Inc. Seminars in Nuclear Medicine, Vol. 6, No. 1 (January), 1976
33
Table 1. Osteoid Osteomas
Spine Long bones Femoral neck Talus Skull
Totol
Scan +
X-roy +
4* .5 7 2 1
4 5 7 2 1
2 4t 6'1" 1t 1
*One not operated on; being followed clinically. 1"Subsequentlydelineated by special radiography.
,dr t R 6
L.
Fig. !. Intertrochanterlc osteoid osteoma. (A) Pinhole view of right hip showing focal " h o t " spot near lesser trochanter. (B) Normal left hip. (C) Radiograph showing questionable abnormality prior to scan. (D) Appropriate view, after scan pinpointed the abnormality, demonstrates'the lesion. 34
BENIGN TUMORS
35
:.~.. - ". !'r
9 ..": :. "~r
.2~'.
." ::.2.-.
..,..
9 "., " "" "~.-'.'-"..i"' " : .. :.""'.~C ~:.' : . 9 :"L-,~;'L.-
.? ",_~....
- ....~.,..:-~... L~" ":-"
--" "-:
I_ ~ ~ : : ~-*.. ~ ....
9
.
R
A
Fig. 2. Spinal osteoid osteoma. (A) Posterior scan of lumbar spine and pelvis, showing obvious focal accumulation of activity on the right at L-5-5-1. (B) This was only recognized on additional radiographs done afterwards, as an area of sclerosis involving the right ala of 5-1 and the inferior articular facet and pedicle of L-5.
a high information density. We collect 2000-3000 counts per square centimeter over the shaft of the bone in the metaphyseal region, using a 25,000-hole collimator. Magnification views using either a converging collimator or a pinhole collimator for maximum enlargement can frequently help delineate the exact location and extent of the abnormality. OSTEOID OSTEOMA
This is the largest group of benign bone neoplasms that we have encountered. To date, we have diagnosed 19 osteoid osteomas, 15 of which have been confirmed surgically and four are being followed clinically (Table I). The most c o m m o n indication for studying this group was to determine the cause o f bone
36
GILDAY AND ASH
P
O P A
13
Vx
f
C
Fig. 3. Osteoma of left occiput. (A) Bloodpool images demonstrate the vascular nature of the asteoma, which is obvious on the delayed posterior view (B) and the vertex view (C).
pain. Almost invariably, the history was atypical and the diagnosis was in question radiologically. When there was a suspicious radiologic change, confirmation of the presence ofan osteoid osteoma was possible by the bone scan. Even when no radiologic changes were evident, the bone scan detected several osteoid osteomas. Radiologicaily, it is difficult to evaluate osteoid osteomas in certain areas of the body, namely the spine, the femoral neck region, and the small bones of the feet (Table 1). In such instances, the complete nuclear medicine study with high information density, multiple-view bone scans, and pinhole magnification has been necessary in the diagnosis of an osteoid osteoma. Subsequent radiologie tomography, in the appropriate projection, usually confirmed the presence of the osteoid osteoma. In several of our cases, tomography was not positive and the bone scan had to be used to locate the lesion immediately prior to surgery.
BENIGN TUMORS
37
P
13
Fig. 4. Fracture through a simple bone cyst. (A) The tomogram shows a simple bone cyst in the right femoral neck with a questionable linear lucency across its lower portion, but not diagnostic of fracture. (B) The marked uptake in this area on the bone scan confirms that trauma occurred. (C) The pinhole view demonStrates increased uptake around the fracture at the lower portion of the cyst, which can be seen as a relatively cooler area above.
,.JiIdlb~.
"' '~"
"."i C
We have found that it is almost always necessary to do pinhole imaging of the hip region to delineate the exact location of femoral neck or intertrochanteric-region osteoid osteomas (Fig. 1). Quite frequently, the child's severe pain precludes proper positioning for the standard radiographs of the femur. However, once a lesion has been demonstrated by bone scan, it is imperative to
38
GILDAY AND ASH
.
?.,.
R
B
L
ANT
Fig. 5. Nonossifying fibroma. (A) The radiograph shows a lesion in the left tiblal metaphysis diagnosed as a nonossifying flbroma. (B) Bone scan of the knees demonstrates a corresponding minimal increase in activity at the medial aspect of the left tibia when compared with the normal right.
obtain appropriate radiographic views of the area, using sedation and analgesics if necessary. The bone scan is probably least valuable in osteoid osteomas of the long bones, since the radiologic diagnosis is usually definitive. The converse is true in the spine. Not only is it difficult to evaluate this area radiologically, but frequently the children are treated for other causes o f back pain and the investigation for osteoid osteoma is not performed. We have had several such cases, each with a long and complicated history. In two instances, symptoms were present for more than 2 years and each boy had had significant orthopedic and neurosurgical intervention for back pain. In both cases, it was very obvious from the nuclear medicine study that there was an osteoid osteoma present in the spine (Fig. 2). In one case, the additional radiographs subsequently demonstrated a very abnormal superior articular facet of the vertebral body. This was removed with immediate resolution of the patient's symptoms. In the other, tomograms were normal and the patient h a d to have a preoperative localization of the osteoid osteoma by bone scanning. This was successful and enabled the surgeons to find the osteoid osteoma, which was confirmed pathologically.
Fig. 6. Osteogenic sarcoma of femur. (A) Radiograph of the left knee shows cortical destruction with new bone formation and a soft-tissue mass at the latoral femoral condyle. (B) The blood-pool image demonstrates typical marked hyperemia to the entire metaphysis and adjacent soft tissue laterally is more extensive than the radiologic abnormality. (C) There is a corresponding area of avid uptake on the delayed scan, most marked laterally.
o
9
9
r
":,'"
it AN E3P I.'1"
B
C 39
40
GILDAY AND ASH
0
POST
R
A
Fig. 7. Osteochondroma, right tibia. (A) The posterior and (B) right lateral scans demonstrate increased uptake limited to the bony prominence seen in the radiograph (C).
BENIGN TUMORS
41
9
:-'!
...., :v"
9
9
.
9
9
-..:~.:.
.
:. ". ". '.'i.:~-'
"
ANT
;'..~....
, . ,
"~'1". 9. 9
C
.-.
.
C] n
.
R
L.
L
..
D
Fig. 8. Sessile osteochondrema, leh femur. (A and B) Radiographs show cortical thickening and apparent destruction above the medial metaphysis with soft-tissue swelling, thought to be a possible sarcoma. (C) The blood image shows no appreciable hyperemia to this area, and (D) the delayed scan demonslrates only minor increased uptake at the site, making the diagnosis of malignancy very unlikely.
42
GILDAY AND ASH
B~ See legend facing page.
BENIGN TUMORS
43
R
A
L
T C MOPN BF
C
D ANT
L
POST
E Fig. 9. Recurrent fibrous dysplasia. This patien't had a craniectomy for fibrous dysplasia 3 years ago and was scanned for reassessment of progression. Radiographs shown in (A and B) demonstrate the bony abnormalities. These are more cleady delineated by the anterior bloodpool image (C) with increased vascularity over the left hemisphere, middle and anterior cranial fossae. The anterior (D) and left lateral (E) delayed images demonstrate avid uptake in the same areas, with a coo[ defect at the previous craniotomy site.
44
GILDAY AND ASH
Ivory osteomas in the skull are also highly vascular and have the same highly intense concentration of the bone radiopharmaceutical as the osteoid osteoma (Fig. 3). CYSTS
T h e r e are two common types of cysts: the simple cyst and the aneurysmal bone cyst. There does not appear to be any significant difference between these on the bone scan. The usual appearance is either minimal or no increase in radioactivity at the site of the cyst. This is not surprising, since the bone is usually not very active metabolically. The bone scan is mainly valuable in determining whether a radiologically lucent lesion is a benign cyst. In our experience the cyst is not " h o t " unless it is traumatized. When a cyst is fractured, the radiographs may be normal and even the tomographic evaluation of the cyst can be equivocal, whereas the bone scan is extremely sensitive in determining whether or not a fracture has occurred (Fig. 4). Cortical defects in bone have a similar appearance to cysts. We have examined seven to date and, in our experience and that of others, the scan is always normal. 6 OTHER NEOPLASMS
Aside from osteoid osteomas, there are few definitely benign bone neoplasms; however, the ones that do occur are most commonly found in children. The n0nossifying fibroma presents as a cystic structure radiologically and usually has a mild increase in radioactivity in the bone scan (Fig. 5). Our experience is similar to reports in the literature that low-grade bone uptake rules out a sarcoma, which typically has an avid accumulation of the radiopharmaceutical and is very hyperemic in the blood-pool images (Fig. 6). However, some benign neoplasms such as osteochondromas, may also show a similar marked increase in activity. 4 The references in the literature concerning the uptake of the radiopharmaceutical by lesions such as enchondromas and osteochondromas have been varied. 7 We have found that osteochondromas generally show very active accumulation o n the bone scan only at the site of bone growth (Fig. 7),. and the diagnosis is usually evident radiologically. However, some sessile osteochondromas and some enchondromas may mimic the appearance of a paraosteal sarcoma on the radiograph. Our experience has shown, however, that these will have a much lower uptake of the radiopharmaceutical than would a malignant lesion (Fig. 8). In some cases, the osteochondromas approach normal bone activityand may not be recognized if the site is unusual. Fibrous dysplasia, on the other hand, has a much more dramatic appearance on the bone scan. It is extremely hyperemic and there is very marked uptake of the radiopharmaceutical on the delayed image. In such instances, it is difficult to differentiate these lesions from a malignant tumor, (long-standing) osteomyelitis, or bone trauma with subperiosteal reaction. The diagnosis is usually made radiologically. The bone scan appears to be most helpful in delineating the extent of the fibrous dysplasia and its recurrence postoperatively (Fig. 9).
BENIGN TUMORS
45
POST
L
POBT
R
R
9
..1 ~. ,,,.~. '
..
9
.'o
.
~,.
,
B
Fig. 10. Eosinophiffc granuloma, right s~apula. (A) The totc!l-body rectilinear scan shows abnormal increased uptake in the region of the right shaulder only. ( " H o t " area in soft tissues of right elbow represents injection site.) (B) On the scintillation camera view, the lesion is localized to the scapula, with uptake mainly around its periphery. (C) Radiograph of the lesion. A second lucent lesion at the distal end of the right femur had a different appearance on the radiograph and showed normal activity on the scan, indicating that it was of a differing nature, i.e., a fibrous cortical defect.
46
GILDAY AND ASH RETICULOSES
There are two basic reticuloses affecting bone. The m o s t c o m m o n one is that o f the histiocytosis X g r o u p , o f which the benign type is the eosinophilic g r a n u l o m a . These have traditionally been g r o u p e d as a reticulosis, although recent t h e o r y indicates that they should be classified separately. T h e b o n e scan can help determine whether or not the histiocytic lesion is solitary, which would m a k e it an eosinophilic g r a n u l o m a or multiple, which w o u l d tend to put it into the m o r e malignant g r o u p o f the histiocytosis X. In o u r experience, the b o n e scan is almost always positive in the eosinophilic g r a n u l o m a (Fig. 10). We have had only one false negative in ten scans.' A n unusual g r o u p o f patients is that with G a u c h e r ' s disease. A l t h o u g h they do not strictly have a benign neoplasm, they do fall into the g r o u p o f patients whose b o n e lesions are often lytic. T h e involved bones d e m o n s t r a t e a vague increase in activity with deformity o f the b o n e itself. In such instances, it is useful to p e r f o r m pinhole imaging o f the hip, since these patients frequently develop avascular necrosis o f the femoral head. REFERENCES
I. Subramanian G, McAfee JG: A new complex of 99mTc for skeletal imaging. Radiology 99:192, 1971 2. Samuels LD: Skeletal scintigraphy in children. Semin Nucl Med 3:89-107, 1973 3. Bell EG, Mahon DF: Bone, in Handmaker tl, Lowenstein JM (eds): Nuclear Medicine in Clinical Pediatrics. New York, The Society of Nuclear Medicine, 1975 4. Bell EG, Subramanian G, Blair RJ, et al:
Bone scanning in pediatrics, in James AE, Wagner tIN Jr, Cooke RE (eds): Pediatric Nuclear Medicine. Philadelphia, Saunders, 1974 5. Gilday DL: Diagnosis of obscure childhood osteoid osteomas with the bone scan. J Nucl Med 15:494, 1.974(abstract) 6. Madj M: Personal communication. 1975 7. Moon NF, Dworkin HJ, LaFleur PD: Clinical use of sodium fluoride-18F in bone photoscanning. JAMA 204:974, 1968
