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Intraosseous lipoma of the calcaneus: a report of 3 cases
The Foot (199414.
166-170
Intraosseous lipoma of the calcaneus: a report of 3 cases P. N. M. Tyrreli, A. M. Davies, I. Beggs MRI Centre, Royal Orthopaedic Hospital, Birmingham, and Department of Radiology, Princess Margaret Rose Orthopaedic Hospital, Edinburgh S UMMA R Y. Intraosseous lipomata are rare benign bone lesions, the diagnosis of which is not always immediately obvious on plain radiography. Three cases in the calcaneus are described with particular reference to the appearances on CT and MRI, which may be diagnostic.
Intraosseous lipoma is a rare benign bone tumour. The plain radiographic appearances are variable ranging from a well demarcated pure radiolucent lesion to one containing differing amounts of calcification depending upon its stage of involution.’ We present 3 cases of an intraosseous lipoma occurring in the calcaneus and discuss the value of computed tomography (CT) and magnetic resonance imaging (MRI) in the assessment of such a lesion. The imaging appearances in relation to the histological changes which can occur during the involution of such a lesion are also discussed.
intensity than the adjacent fat (Fig. 4). Both CT and MRI examinations confirmed that the lesion was confined to the marrow cavity, with no cortical expansion or involvement and no surrounding soft tissue mass. The appearances on the imaging studies were considered diagnostic of an intraosseous lipoma. Case 2 A 44-year-old lady presented with a 2-year history of left heel pain. She was otherwise well. On examination, swelling and tenderness were present around the heel and movement at the subtalar joint was restricted. Radiographs showed a well defined lucent lesion lying centrally in the calcaneus. It had a thin sclerotic margin and fine vertical and transverse bony septations. Scintigraphy showed increased activity in the left hind- and midfoot. CT confirmed that the lesion was well defined and contained a relatively thick vertical bony septum (Fig. 5). It was otherwise of homogeneously low attenuation (- 108 Hounsfield Units). Sagittal and coronal Tl and T2 weighted MR scans showed the lesion to be well defined. It contained a bony septum and a solitary small signal void in keeping with a focus of calcification (Fig. 6). Although the lesion was of slightly increased signal intensity compared with adjacent calcaneal bone on both TlW and T2W images, it was noted to be of similar signal intensity to the marrow cavity of the distal tibia, in keeping with fat consistency. Histological examination confirmed the diagnosis of an intraosseous lipoma.
CASE REPORTS Case 1 A 27-year-old man presented with a 18-month history of pain in the left heel. Clinical examination was unremarkable. Radiographic examination of the left ankle and calcaneus revealed a rounded lucency in the anterior aspect of the calcaneus, which contained a large focus of calcification centrally (Fig. 1). CT showed a well defined lesion in the anterior aspect of the calcaneus with negative attenuation consistent with fat, and a central focus confirmed to be of calcific density (Fig. 2). MRI of the lesion was performed comprising sagittal and coronal Tl weighted (Tl W) and axial dual echo sequences. The TlW images showed a lesion demarcated by a very thin margin of low signal in keeping with a fine sclerotic rim, with areas of signal intensity marginally lower than the surrounding marrow fat (Fig. 3). The low signal thin strands within the lesion were consistent with persisting trabeculae. A central focus of signal void was representative of the central area of calcification. T2 weighted (T2W) axial images showed a lesion with areas of slightly higher signal
Case 3 A 12-year-old boy presented with pain in the left hindfoot. He had injured the foot about 7 years 166
Intraosseous lipoma of the calcaneus: a report of 3 cases
Fig. l-Radiograph
167
of the left calcaneus (case 1) showing a well defined intraosseous lipoma containing a central focus of calcification.
On examination, hindfoot movement on the left was restricted and the heel was held in valgus. Radiographic examination showed a small lucent area with a thin sclerotic margin in the left calcaneus adjacent to the sustentaculum. CT confirmed that the lesion was of fatty density and that it had a thin sclerotic margin (Fig. 7). The lesion was curetted and histology confirmed an intraosseous lipoma.
DISCUSSION
Fig. 2-Coronal CT scan of the left calcaneus (case 1) showing a lesion of fat attenuation and a central focus of calcification.
previously. No fracture was identified at that time but the foot was immobilized in plaster. Subsequently, he continued to experience pain and walked with the foot externally rotated.
Intraosseous lipoma is an uncommon benign bone tumour, accounting for less than 1% of all benign bone neoplasms.’ With the increasing usage of both CT and MRI, these lesions are being more frequently detected and this figure may well be an underestimation of their true frequency. This tumour has been extensively studied by Milgram, who, in his series of 66 cases found the common sites of occurrence to be the proximal femur, followed by the calcaneus and ilium, but that it could involve almost any bone in the body.3 Approximately 50% of patients present with localized pain or swelling, but often the lesion is asymptomatic and is discovered incidentally.3 Malignant transformation has been described, but appears to be exceedingly rare.’ Its characteristic appearance on plain radiography is that of a well defined radiolucency which may contain varying amounts of calcification (Fig. 1). and, depending on its stage of involution, be surrounded by a marginal and reactive sclerosis.’ zone of calcification
168 The Foot
Fig. 3-Sagittal TlW-SE MR image showing a lesion in the calcaneus (case 1) with signal intensity marginally lower than surrounding marrow fat and a central signal void consistent with calcification.
Fig. 5--Coronal
CT scan through the calcaneus of case 2, showing a lesion of fat attenuation and traversed by a vertical bony septum.
Fig. 4-Axial
TZW-SE MR image through the calcaneus (case 1) showing a lesion of slightly higher signal intensity than the surrounding marrow fat with a central signal void consistent with calcification.
Histological correlation with these radiographic findings explains the variable features. Milgram identified three stages in the involution of an intraosseous lipoma:3qs stage 1, where the lesion consists purely of viable fat cells; stage 2 - a transitional lesion composed partly of viable fat cells with partial necrosis of the lesional fat cells and calcification of these necrotic foci; and stage 3 -
Intraosseous
Fig. 6-Sagittal TIW-SE image (case 2), showing a well defined lesion in the calcaneus with signal intensity similar to the distal tibia and containing a focus of signal void due to calcification. A vertical septum is also present.
Fig. 71Coronal CT scan through the left calcaneus (case 3), showing a well defined lesion of fat attenuation consistent with a lipoma.
lipoma
of the calcaneus:
a report
of 3 cases
169
lesions consisting of necrotic fat cells with secondary calcification and reactive woven bone formation. Depending on the stage of involution at which the lesion is identified, its radiographic appearance will differ and the differential diagnosis will similarly alter. A recent paper has described the CT appearances in relation to involutionary changes6 Stage 1 lesions are quite radiolucent, may be expansile and can be confused with a simple bone cyst or an aneurysmal bone cyst. While CT conveys little extra information over plain radiographs in the specific identification of malignant tumours, it is helpful in the further assessment of benign lesions due to evaluation of intralesional attenuation values.7~8 Despite the negative attenuation levels associated with an intraosseous lipoma, CT is not always diagnostic as lesions containing histiocytes laden with fat vacuoles or areas of fatty degeneration resulting from infarction may yield relatively low CT values. 7 Stage 2 lesions may be confused with an enchondroma or a chondrosarcoma. Both CT and MRI will be valuable in diagnosis here. On MRI most tumours will be associated with lengthening of both the Tl and T2 relaxation times, leading to a reduced signal on the TlW images and an increase in signal on the T2W images. A STIR sequence suppresses signal from fat, but abnormal tissues with prolonged Tl and T2 relaxation times will have a markedly increased signal. Although MRI in general lacks tissue specificity, a predominantly fatty lesion such as a lipoma will be suggested due to signal isointense with fat and to its suppression of signal on STIR images. A STIR sequence was not carried out in any of these patients as the Tl W and T2W sequences together with the CT appearances were considered sufficiently diagnostic. Stage 3 lesions often have to be differentiated from a bone infarct.5 Cyst formation is an important differentiating feature. Prior bone resorption must occur at the site where the cyst forms and this resorption process can be mediated only by osteoclasts to facilitate cellular expansion of the lesional cells. Infarcted bone itself is incapable of resorbing bone. The MRI appearances of a pure stage 1 lipoma demonstrate the signal intensity of the lesion to be isointense with that of marrow fat on all sequences.’ Case 2 showed the lesion essentially to be isointense with marrow fat on both the Tl W and T2W images. While this suggests that the lesion is indeed a pure stage 1 lipoma, the presence of a small focus of calcification negates this, and implies more probably a stage 2 lesion ( Fig. 6). In case 1, the TI W image showed part of the lesion to be of slightly lower signal intensity than surrounding marrow fat (Fig. 3), and on the T2W image the signal from part of the lesion was of slightly higher signal intensity in a heterogeneous distribution than the surrounding
170 The Foot
marrow (Fig. 4). While in this case, these findings may be artefactual due to volume averaging, they may represent the signal characteristics of fluid and thus suggest areas of early necrosis or cyst formation as previously described.’ Should a medullary infarct have entered the differential diagnosis, then the MRI appearances will clarify. On MRI, an early medullary infart will appear as a poorly defined region of low signal intensity on TlW images and of increased signal intensity on T2W images. The older established infarct will demonstrate geographic abnormalities with a serpiginous low intensity rim. The central marrow regains signal intensity that is isointense to the surrounding unaffected marrow.” The calcaneus is the common site for an intraosseous lipoma in the foot.3 It occurs in the same location as a simple cyst, yet is at least 10 times less common,r’ and as alluded to above, may give rise to diagnostic confusion. The imaging appearances on CT and MRI are characteristic and will obviate the need for histological confirmation in the majority of cases.
4. Milgram J W. Malignant transformation in bone lipomas. Skeletal Radio1 1990; 19: 347-352. 5. Milgram J W. Intraosseous lipoma: radiologic and pathologic manifestations. Radiology 1988; 167: 1555160. 6. Wiliams C E, Close P J, Meaney J, Ritchie D, Cogley D, Carty A T. Intraosseous lipomas. Clin Radio1 1993; 47: 348-350. 7. Ramos A, Caste110 J, Sartoris D J, Greenway G D, Resnick D, Haghighi P. Osseous lipoma: CT aonearances. Radioloav 1985: 157: 615-619. 8. I%g-Boix V, Guinot-Tormo J, Risen&Martinez F, Aparisi-Rodriguez F, Ferrer-Jimenez R. Computed tomography of intraosseous lipoma of OScalcis. Comnuted Tomoeranhv 1987: 221: 286-291. 9. De&h A L, MmkJ H, Kerr R. Tumors and tumorlike lesions of soft tissue and bone. In: MRI of the foot and ankle. New York: Raven Press, 1992; 2599261. 10. Moore S G. Paediatric musculoskeletal imaging. In: Stark D D, Bradley W G, eds. Magnetic resonance imaging. 2nd ed. St Louis: Mosby Year Book, 1992; 2307. 11. Richter G M, Ernst H U, Dinkel E et al. Morphologie und diagnostik von knocken tumoren des fusses. Radiologie 1986; 26: 341-352.
The authors P. N. M. Tyrrell FRCR A. M. Davies FRCR
References Milgram J W. Intraosseous lipomas with reactive ossification in the proximal femur. Skeletal Radio1 1981; 7: I-13. Dahlin D C and Unni. Bone tumours. General aspects and data on 8542 cases. 4th ed. Springfield: Charles C Thomas, 1986. Milgram J W. Intraosseous lipoma. A clinicopathological study of 66 cases. Clin Orthop 1988; 231: 277-303.
MRI Centre Royal Orthopaedic Hospital Bristol Road South Birmingham B31 2AP UK I. Reggs FRCR
Department of Radiology Princess Margaret Rose Orthopaedic Hospital Edinburgh UK Correspondence to Dr A. M. Davies.
166-170
Intraosseous lipoma of the calcaneus: a report of 3 cases P. N. M. Tyrreli, A. M. Davies, I. Beggs MRI Centre, Royal Orthopaedic Hospital, Birmingham, and Department of Radiology, Princess Margaret Rose Orthopaedic Hospital, Edinburgh S UMMA R Y. Intraosseous lipomata are rare benign bone lesions, the diagnosis of which is not always immediately obvious on plain radiography. Three cases in the calcaneus are described with particular reference to the appearances on CT and MRI, which may be diagnostic.
Intraosseous lipoma is a rare benign bone tumour. The plain radiographic appearances are variable ranging from a well demarcated pure radiolucent lesion to one containing differing amounts of calcification depending upon its stage of involution.’ We present 3 cases of an intraosseous lipoma occurring in the calcaneus and discuss the value of computed tomography (CT) and magnetic resonance imaging (MRI) in the assessment of such a lesion. The imaging appearances in relation to the histological changes which can occur during the involution of such a lesion are also discussed.
intensity than the adjacent fat (Fig. 4). Both CT and MRI examinations confirmed that the lesion was confined to the marrow cavity, with no cortical expansion or involvement and no surrounding soft tissue mass. The appearances on the imaging studies were considered diagnostic of an intraosseous lipoma. Case 2 A 44-year-old lady presented with a 2-year history of left heel pain. She was otherwise well. On examination, swelling and tenderness were present around the heel and movement at the subtalar joint was restricted. Radiographs showed a well defined lucent lesion lying centrally in the calcaneus. It had a thin sclerotic margin and fine vertical and transverse bony septations. Scintigraphy showed increased activity in the left hind- and midfoot. CT confirmed that the lesion was well defined and contained a relatively thick vertical bony septum (Fig. 5). It was otherwise of homogeneously low attenuation (- 108 Hounsfield Units). Sagittal and coronal Tl and T2 weighted MR scans showed the lesion to be well defined. It contained a bony septum and a solitary small signal void in keeping with a focus of calcification (Fig. 6). Although the lesion was of slightly increased signal intensity compared with adjacent calcaneal bone on both TlW and T2W images, it was noted to be of similar signal intensity to the marrow cavity of the distal tibia, in keeping with fat consistency. Histological examination confirmed the diagnosis of an intraosseous lipoma.
CASE REPORTS Case 1 A 27-year-old man presented with a 18-month history of pain in the left heel. Clinical examination was unremarkable. Radiographic examination of the left ankle and calcaneus revealed a rounded lucency in the anterior aspect of the calcaneus, which contained a large focus of calcification centrally (Fig. 1). CT showed a well defined lesion in the anterior aspect of the calcaneus with negative attenuation consistent with fat, and a central focus confirmed to be of calcific density (Fig. 2). MRI of the lesion was performed comprising sagittal and coronal Tl weighted (Tl W) and axial dual echo sequences. The TlW images showed a lesion demarcated by a very thin margin of low signal in keeping with a fine sclerotic rim, with areas of signal intensity marginally lower than the surrounding marrow fat (Fig. 3). The low signal thin strands within the lesion were consistent with persisting trabeculae. A central focus of signal void was representative of the central area of calcification. T2 weighted (T2W) axial images showed a lesion with areas of slightly higher signal
Case 3 A 12-year-old boy presented with pain in the left hindfoot. He had injured the foot about 7 years 166
Intraosseous lipoma of the calcaneus: a report of 3 cases
Fig. l-Radiograph
167
of the left calcaneus (case 1) showing a well defined intraosseous lipoma containing a central focus of calcification.
On examination, hindfoot movement on the left was restricted and the heel was held in valgus. Radiographic examination showed a small lucent area with a thin sclerotic margin in the left calcaneus adjacent to the sustentaculum. CT confirmed that the lesion was of fatty density and that it had a thin sclerotic margin (Fig. 7). The lesion was curetted and histology confirmed an intraosseous lipoma.
DISCUSSION
Fig. 2-Coronal CT scan of the left calcaneus (case 1) showing a lesion of fat attenuation and a central focus of calcification.
previously. No fracture was identified at that time but the foot was immobilized in plaster. Subsequently, he continued to experience pain and walked with the foot externally rotated.
Intraosseous lipoma is an uncommon benign bone tumour, accounting for less than 1% of all benign bone neoplasms.’ With the increasing usage of both CT and MRI, these lesions are being more frequently detected and this figure may well be an underestimation of their true frequency. This tumour has been extensively studied by Milgram, who, in his series of 66 cases found the common sites of occurrence to be the proximal femur, followed by the calcaneus and ilium, but that it could involve almost any bone in the body.3 Approximately 50% of patients present with localized pain or swelling, but often the lesion is asymptomatic and is discovered incidentally.3 Malignant transformation has been described, but appears to be exceedingly rare.’ Its characteristic appearance on plain radiography is that of a well defined radiolucency which may contain varying amounts of calcification (Fig. 1). and, depending on its stage of involution, be surrounded by a marginal and reactive sclerosis.’ zone of calcification
168 The Foot
Fig. 3-Sagittal TlW-SE MR image showing a lesion in the calcaneus (case 1) with signal intensity marginally lower than surrounding marrow fat and a central signal void consistent with calcification.
Fig. 5--Coronal
CT scan through the calcaneus of case 2, showing a lesion of fat attenuation and traversed by a vertical bony septum.
Fig. 4-Axial
TZW-SE MR image through the calcaneus (case 1) showing a lesion of slightly higher signal intensity than the surrounding marrow fat with a central signal void consistent with calcification.
Histological correlation with these radiographic findings explains the variable features. Milgram identified three stages in the involution of an intraosseous lipoma:3qs stage 1, where the lesion consists purely of viable fat cells; stage 2 - a transitional lesion composed partly of viable fat cells with partial necrosis of the lesional fat cells and calcification of these necrotic foci; and stage 3 -
Intraosseous
Fig. 6-Sagittal TIW-SE image (case 2), showing a well defined lesion in the calcaneus with signal intensity similar to the distal tibia and containing a focus of signal void due to calcification. A vertical septum is also present.
Fig. 71Coronal CT scan through the left calcaneus (case 3), showing a well defined lesion of fat attenuation consistent with a lipoma.
lipoma
of the calcaneus:
a report
of 3 cases
169
lesions consisting of necrotic fat cells with secondary calcification and reactive woven bone formation. Depending on the stage of involution at which the lesion is identified, its radiographic appearance will differ and the differential diagnosis will similarly alter. A recent paper has described the CT appearances in relation to involutionary changes6 Stage 1 lesions are quite radiolucent, may be expansile and can be confused with a simple bone cyst or an aneurysmal bone cyst. While CT conveys little extra information over plain radiographs in the specific identification of malignant tumours, it is helpful in the further assessment of benign lesions due to evaluation of intralesional attenuation values.7~8 Despite the negative attenuation levels associated with an intraosseous lipoma, CT is not always diagnostic as lesions containing histiocytes laden with fat vacuoles or areas of fatty degeneration resulting from infarction may yield relatively low CT values. 7 Stage 2 lesions may be confused with an enchondroma or a chondrosarcoma. Both CT and MRI will be valuable in diagnosis here. On MRI most tumours will be associated with lengthening of both the Tl and T2 relaxation times, leading to a reduced signal on the TlW images and an increase in signal on the T2W images. A STIR sequence suppresses signal from fat, but abnormal tissues with prolonged Tl and T2 relaxation times will have a markedly increased signal. Although MRI in general lacks tissue specificity, a predominantly fatty lesion such as a lipoma will be suggested due to signal isointense with fat and to its suppression of signal on STIR images. A STIR sequence was not carried out in any of these patients as the Tl W and T2W sequences together with the CT appearances were considered sufficiently diagnostic. Stage 3 lesions often have to be differentiated from a bone infarct.5 Cyst formation is an important differentiating feature. Prior bone resorption must occur at the site where the cyst forms and this resorption process can be mediated only by osteoclasts to facilitate cellular expansion of the lesional cells. Infarcted bone itself is incapable of resorbing bone. The MRI appearances of a pure stage 1 lipoma demonstrate the signal intensity of the lesion to be isointense with that of marrow fat on all sequences.’ Case 2 showed the lesion essentially to be isointense with marrow fat on both the Tl W and T2W images. While this suggests that the lesion is indeed a pure stage 1 lipoma, the presence of a small focus of calcification negates this, and implies more probably a stage 2 lesion ( Fig. 6). In case 1, the TI W image showed part of the lesion to be of slightly lower signal intensity than surrounding marrow fat (Fig. 3), and on the T2W image the signal from part of the lesion was of slightly higher signal intensity in a heterogeneous distribution than the surrounding
170 The Foot
marrow (Fig. 4). While in this case, these findings may be artefactual due to volume averaging, they may represent the signal characteristics of fluid and thus suggest areas of early necrosis or cyst formation as previously described.’ Should a medullary infarct have entered the differential diagnosis, then the MRI appearances will clarify. On MRI, an early medullary infart will appear as a poorly defined region of low signal intensity on TlW images and of increased signal intensity on T2W images. The older established infarct will demonstrate geographic abnormalities with a serpiginous low intensity rim. The central marrow regains signal intensity that is isointense to the surrounding unaffected marrow.” The calcaneus is the common site for an intraosseous lipoma in the foot.3 It occurs in the same location as a simple cyst, yet is at least 10 times less common,r’ and as alluded to above, may give rise to diagnostic confusion. The imaging appearances on CT and MRI are characteristic and will obviate the need for histological confirmation in the majority of cases.
4. Milgram J W. Malignant transformation in bone lipomas. Skeletal Radio1 1990; 19: 347-352. 5. Milgram J W. Intraosseous lipoma: radiologic and pathologic manifestations. Radiology 1988; 167: 1555160. 6. Wiliams C E, Close P J, Meaney J, Ritchie D, Cogley D, Carty A T. Intraosseous lipomas. Clin Radio1 1993; 47: 348-350. 7. Ramos A, Caste110 J, Sartoris D J, Greenway G D, Resnick D, Haghighi P. Osseous lipoma: CT aonearances. Radioloav 1985: 157: 615-619. 8. I%g-Boix V, Guinot-Tormo J, Risen&Martinez F, Aparisi-Rodriguez F, Ferrer-Jimenez R. Computed tomography of intraosseous lipoma of OScalcis. Comnuted Tomoeranhv 1987: 221: 286-291. 9. De&h A L, MmkJ H, Kerr R. Tumors and tumorlike lesions of soft tissue and bone. In: MRI of the foot and ankle. New York: Raven Press, 1992; 2599261. 10. Moore S G. Paediatric musculoskeletal imaging. In: Stark D D, Bradley W G, eds. Magnetic resonance imaging. 2nd ed. St Louis: Mosby Year Book, 1992; 2307. 11. Richter G M, Ernst H U, Dinkel E et al. Morphologie und diagnostik von knocken tumoren des fusses. Radiologie 1986; 26: 341-352.
The authors P. N. M. Tyrrell FRCR A. M. Davies FRCR
References Milgram J W. Intraosseous lipomas with reactive ossification in the proximal femur. Skeletal Radio1 1981; 7: I-13. Dahlin D C and Unni. Bone tumours. General aspects and data on 8542 cases. 4th ed. Springfield: Charles C Thomas, 1986. Milgram J W. Intraosseous lipoma. A clinicopathological study of 66 cases. Clin Orthop 1988; 231: 277-303.
MRI Centre Royal Orthopaedic Hospital Bristol Road South Birmingham B31 2AP UK I. Reggs FRCR
Department of Radiology Princess Margaret Rose Orthopaedic Hospital Edinburgh UK Correspondence to Dr A. M. Davies.