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Case Report

Vertebral intraosseous lipoma

Lt Col Debraj Sen a,*, Brig Lovleen Satija b, Col Samar Chatterji c, Anusree Majumder d,Meenu Singh e, Aakansha Gupta e

aClassified Specialist (Radiodiagnosis), Command Hospital (Central Command), Lucknow 226002, IndiabConsultant & Professor (Radiodiagnosis), Command Hospital (Central Command), Lucknow, IndiacAssociate Professor, Department of Radiodiagnosis, Armed Forces Medical College, Pune 40, IndiadResident (Pathology), Command Hospital (Eastern Command), Kolkata, IndiaeResident (Radiodiagnosis), Command Hospital (Central Command), Lucknow, India

a r t i c l e i n f o

Article history:

Received 19 December 2012

Accepted 1 May 2013

Available online xxx

Keywords:

Vertebra

Intraosseous

Lipoma

Computerized Tomography

Magnetic resonance imaging

* Corresponding author. Tel.: þ91 9670574817E-mail address: sendebraj@gmail.com (D

Please cite this article in press as: Sen D, edx.doi.org/10.1016/j.mjafi.2013.05.001

0377-1237/$ e see front matter ª 2013, Armhttp://dx.doi.org/10.1016/j.mjafi.2013.05.001

Introduction

Lipomatous tumours are ubiquitous and the commonest tu-

mours to affect soft tissues. Despite the fat content of bone

medulla, intra-osseous lipoma is the rarest primary tumour to

afflict bones.1 Here we present an unusual case of vertebral

intraosseous lipoma in a young male with low backache. This

article aims to discuss and highlight the radiological and

pathological features of this rare entity which may often be

missed or misinterpreted.

(mobile).. Sen).

t al., Vertebral intraosse

ed Forces Medical Service

Case report

A 35-year-old male patient presented with chronic low back-

acheofoneyearduration thatwas insidious inonset,moderate

in intensity and aggravated byprolonged standing. Thepatient

did not have radiculopathy or neurogenic claudication. There

wasnohistoryof anycomorbidcondition,medicationor spinal

trauma. The patient’s vital parameters were normal. Lower

paraspinal muscle spasm was noted. There was no point

tenderness, swelling, evidence of sacroiliitis or neurological

deficit. All laboratory investigations were normal.

Lateral radiograph of the lumbosacral spine showed an ill-

defined transradiant lesion in the superior part of L4 vertebral

body (Fig. 1). Computerized Tomography (CT) revealed a

sharply marginated ovoid intraosseous lesion of fat attenua-

tion (�70 Hounsfield Units) at the same location. The lesion

had a thin rim of sclerosis. A punctate calcific focus was noted

within the lesion (Fig. 2). The overlying endplate cortex was

thinned without any obvious disruption. Degenerative

changes in the form of marginal osteophytes and semilunar-

shaped areas of endplate sclerosis were present. Magnetic

Resonance Imaging (MRI) confirmed the CT findings and

revealed a lesion of fat intensity (hyperintense on both T1-

and T2-weighted images). A thin rim hypointense on both T1-

and T2-weighted images consistent with marginal sclerosis

was present. Disc desiccation and Modic changes were also

noted (Fig.3). There was no evidence of sacroiliitis. Based on

these findings a diagnosis of lumbar spondylosis with intra-

osseous lipoma of L4 vertebral body was made.

ous lipoma, Medical Journal Armed Forces India (2013), http://

s (AFMS). All rights reserved.

Fig. 1 e Lateral radiograph of the lumbosacral spine reveals

a subtle transradiant lesion (arrow) in the superior part of

the body of L4 vertebra.

me d i c a l j o u r n a l a rm e d f o r c e s i n d i a x x x ( 2 0 1 3 ) 1e42

Discussion

Fatty tumours affecting bones may be classified as: (a) soft-

tissue lipomata or liposarcomata with secondary bone

involvement; (b) parosteal lipomata, which arise from the

subperiosteal tissue; (c) intraosseous lipomata, which arise

from the medullary cavity; (d) liposarcoma of bone and (e)

liposclerosing myxofibrous tumour.2,3

Fig. 2 e The panel of axial, coronal and sagittal CT images revea

calcific focus in the body of L4 vertebra (arrow).

Please cite this article in press as: Sen D, et al., Vertebral intraossedx.doi.org/10.1016/j.mjafi.2013.05.001

First reported in 1880,4 intraosseous lipoma is the rarest

primary bone tumour with an incidence of 0.1%.3,5,6 However,

recent reports suggest a wider prevalence of up to 2.5%.3,6

Intraosseous lipoma is underreported for many reasons: (a)

non-specific radiographic appearances which may simulate

other entities, (b) benign radiographic appearances which

preclude further CT or MRI, (c) difficulty in histopathologic

interpretation if not correlated with radiology as fat in these

lesions may be indistinguishable from normal fat in yellow

marrow, and osteonecrosis if ischaemic changes are present.3

Intraosseous lipoma has been reported most frequently in

the 4th and 5th decades3,7 and is slightly more common in

males.7

Pain has been reported in up to 66% of cases.3 The aetiology

of pain is speculated to be due to expansile remodelling of

bone or co-existent intralesional ischaemic changes. Patho-

logical fractures occur rarely.1

Most of these tumours occur in the lower limb (71%). The

commonest site is the calcaneum (32%) followed by the

femoral sub-trochanteric region, proximal tibial and distal

femoral shaft and the proximal and distal fibular shaft.7 Upper

limb lesions usually involve the proximal and distal humeral

and radial shafts. They are usually intramedullary, rarely

intracortical and frequently eccentric in smaller long bones.

They have also been reported in the spine,8,9 skull and sino-

nasal cavities,10,11 mandible, pelvis and ribs.5 Multiple intra-

osseous lipomata affecting multiple bones have also been

reported.3,4 Lesion size varies from 10 to 120 mm (mean

39 mm).3,7

The aetiology and nature of intraosseous lipomas is

controversial. While some regard them as benign tumours of

the medullary adipose tissue, others consider them to be

reactive changes secondary to infarcts, infections, or the

result of healed bony infarcts secondary to trauma.12 An as-

sociation with hyperlipoproteinaemia1 and chromosomal

abnormalities has been reported.12 The increased prevalence

of intraosseous lipoma at sites with decreased trabecular

bone, like the calcaneus, has led to the theory that they

represent an ‘overshoot’ of haematopoietic to fatty marrow

conversion, and may therefore be considered hamartomas.3

At gross examination, intraosseous lipomas are pale or

bright yellow, may reveal lobulations with a thin capsule and

septations.3 They are composed of mature adult fat and may

contain a few atrophic trabeculae.

ls a well-delineated lesion of fat attenuation with a central

ous lipoma,Medical Journal Armed Forces India (2013), http://

Fig. 3 e Sagittal T2 e (a) and T1-weighted images (b) reveal a lesion of fat intensity in the body of L4 vertebra adjacent the

superior endplate (arrow). Also noted are disc desiccation and Modic type 2 endplate changes.

med i c a l j o u r n a l a rm e d f o r c e s i n d i a x x x ( 2 0 1 3 ) 1e4 3

Ascribing involutional changes to the histopathologic fea-

tures of intraosseous lipomata, Milgram subdivided them into

3 stages: Stage 1 lesions consist of viable adipocytes without

abnormal cytologic features (normal fat); Stage 2 lesions are

composed of viable adipocytes, fat necrosis and dystrophic

calcification; Stage 3 lesions exhibit extensive fat necrosis,

calcification, cyst formation, reactive peripheral or intrale-

sional ossification, with occasional viable adipocytes.3,12

There is no preponderance of stage 2 and 3 lesions with

advancing age.7 It is speculated that the enlargement of these

lesions in the confined space of the intramedullary canal rai-

ses the intramedullary pressure causing ischaemic fat ne-

crosis and calcification. An alternate theory propounds that

the calcification seen in these tumours might be a product of

the mesenchymal cells in the lesion.3 Stages 2 and 3 lesions

are thus most frequently confused with bone infarct

histologically.

The radiologic appearance of an intraosseous lipoma par-

allels its Milgram stage.3,6 On plain radiography, Milgram

stage 1 lesions are well-circumscribed, transradiant lesions

occasionally associated with mild focal expansile remodel-

ling. Bone expansion is more prominent in thin long bones

such as the fibula. Stage 1 lesion may simulate unicameral

bone cyst, aneurysmal bone cyst, fibrous dysplasia, and

plasmacytoma.3,6 Overall marginal sclerosis and calcification

are seen in 45% and 42% of lesions, respectively, however

these findings are more common in lesions located in the

calcaneum (61%).8 Bone expansion is noted in 33% of sites

Please cite this article in press as: Sen D, et al., Vertebral intraossedx.doi.org/10.1016/j.mjafi.2013.05.001

overall, but infrequently in the calcaneum (13%).7 CT dem-

onstrates the intralesional fat (�600HU to�100 HU), a thin rim

of sclerosis and, if present, expansile remodelling of the

intramedullary canal. On MRI, the intralesional fat appears

similar to subcutaneous fat. Normal yellow marrow shows

signal intensity lower than that of the intraosseous lipoma on

T1-weighted images, related to cellular elements. Fat can also

be demonstrated on MRI by fat suppression sequences.

Milgram stage 2 or 3 lesions appear as transradiant lesions

with central or ring-like calcification or ossification. The

ossification may be extensive, leading to the term ossifying

lipoma.3 A predominantly calcified or ossified lesion may

mimic an enostosis. Partially mineralized lesions may be

mistaken for chondroid lesions or osteonecrosis on radio-

graphs. On CT and MRI, intralesional fat (unless it is

completely calcified or ossified) distinguishes the intra-

osseous lipoma from tumours of chondroid, osteoid, or fibrous

origin. On MRI, calcification is seen as foci of low signal in-

tensity on both T1- and T2-weighted images. Intraosseous li-

poma may be difficult to differentiate from osteonecrosis at

MR imaging and CT because both lesions contain intrinsic fat

with a rim of tissue separating the lesion from surrounding

marrow. Expansile remodelling of bone, osteolysis, and a

rounded rather than irregular serpentine margin suggest an

intraosseous lipoma.

With progressive ischaemia and involution, fibrous prolif-

eration and cystic degeneration occurs in an intraosseous li-

poma (Milgram stage 3 lesions). This and a skeletal

ous lipoma, Medical Journal Armed Forces India (2013), http://

me d i c a l j o u r n a l a rm e d f o r c e s i n d i a x x x ( 2 0 1 3 ) 1e44

distribution similar to unicameral bone cysts in adults has led

to the postulation that unicameral bone cysts may represent

completely involuted intraosseous lipomas. On radiographs,

severely involuted lesions demonstrate a thick peripheral rind

of ossification with variable amounts of central ossification-

calcification producing a distinctive ‘bull’s-eye’ appearance.

Despite the heterogeneous appearance of a severely involuted

intraosseous lipoma on both CT and MR images, the identifi-

cation of intralesional fat permits a definitive diagnosis.

Bone scintigraphy of intraosseous lipomas demonstrates

radionuclide uptake ranging from absent to moderate.3

Intraosseous lipoma in the vertebra may occasionally

mimic haemangioma and osteoporotic bone with increased

fatty marrow.8 Abnormal biomechanical stress due to end-

plate cortical thinning as in our case may be a contributor to

backache and it may be worthwhile to carefully look for these

lesions.

Conclusion

Intraosseous lipoma is the rarest primary bone tumour that

often poses a diagnostic dilemma on plain radiography

because it may be confused with a bone infarct, chondroid

neoplasm, fibrous dysplasia, or other benign conditions. CT

and MRI are helpful in diagnosis by elucidating intralesional

fat.

Conflicts of interest

All authors have none to declare.

Please cite this article in press as: Sen D, et al., Vertebral intraossedx.doi.org/10.1016/j.mjafi.2013.05.001

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