bb5-chap20.pdf

CHAPTER 20

Tumours of Undefined Neoplastic Nature

There are many conditions of bone that are generally consi-

dered non-neoplastic, but often constitute important lesions to

be considered in the differential diagnosis of bone tumours.

Some feature the appearance and cytogenetic characteristics of

neoplasms, although the clinical behaviour rather supports a

non-neoplastic nature. Only the most important conditions are

included in this chapter.

Aneurysmal bone cyst

A.E. Rosenberg

G.P. Nielsen

J.A. Fletcher

Definition

Aneurysmal bone cyst (ABC) is a benign

cystic lesion of bone composed of blood

filled spaces separated by connective

tissue septa containing fibroblasts,

osteoclast-type giant cells and reactive

woven bone. ABC may arise de novo

(primary ABC), or secondarily compli-

cate other benign and malignant bone

tumours (secondary ABC) that have

undergone haemorrhagic cystic change.

Epidemiology

ABC affects all age groups, but is most

common during the first two decades of

life (median age approximately 13 years)

and has no sex predilection {1345,

2200}. The estimated annual incidence is

0.15 per million individuals {1239}.

Primary ABC is well circumscribed and

composed of blood filled cystic spaces

separated by fibrous septa. The fibrous

septa are composed of a moderately

dense cellular proliferation of bland

fibroblasts, with scattered multinucleated

osteoclast-type giant cells and reactive

woven bone rimmed by osteoblasts. The

woven bone frequently follows the con-

tours of the fibrous septa. In approxi-

mately 1/3 of cases the bone is

basophilic and has been termed "blue

bone", however, its presence is not diag-

nostic as it can be seen in other entities.

Mitoses are commonly present and can

be numerous, however, atypical forms

are absent. Necrosis is rare unless there

has been a pathological fracture. The

solid variant of ABC has the same

components as the septa and is very

similar, if not identical, to giant cell repar-

ative granuloma. Primary ABC accounts

for approximately 70% of all cases

{177,1859}.

The majority of secondary ABC develop

in association with benign neoplasms,

most commonly giant cell tumour of

bone, osteoblastoma, chondroblastoma

and fibrous dysplasia {1173,1345, 2200}.

However, ABC-like changes may also

omplicate

Sites of involvement

ABC can affect any bone but usually aris-

es in the metaphysis of long bones espe-

cially the femur, tibia and humerus, and

the posterior elements of vertebral bodies.

Rare tumours whose morphology is iden-

tical to primary ABC of bone have also

been described in the soft tissues {53}.

Synonyms

Multilocular haematic cyst, giant cell

reparative granuloma.

Clinical features / Imaging

The most common signs and symptoms

are pain and swelling, which are rarely

secondary to fracture. In the vertebrae it

can compress nerves or the spinal cord

and cause neurological symptoms.

Radiographically, ABC presents as a lytic,

eccentric, expansile mass with well

defined margins. Most tumours contain a

thin shell of subperiosteal reactive bone.

Computed tomography and magnetic

resonance imaging studies show internal

septa and characteristic fluid-fluid levels

created by the different densities of the

cyst fluid caused by the settling of red

blood cells {1173,2200}. In secondary

ABC, CT and MRI may show evidence of

an underlying primary lesion.

sarcomas,

especially

osteosarcoma.

Macroscopy

ABC is a well defined and multiloculated

mass of blood filled cystic spaces

separated by tan white gritty septa. More

solid areas can be seen which may rep-

resent either a solid portion of the ABC or

a component of a primary tumour that has

undergone secondary ABC-like changes.

Histopathology

ABC may arise de novo (primary ABC),

or secondarily complicate other benign

and malignant bone tumours (secondary

ABC) that have undergone haemorrhagic

cystic change {1281,1557,1699,1849,

1926}.

Fig. 20.01 Aneurysmal bone cyst. A Plain X-ray of

an eccentric lytic mass of the proximal fibula. Note

the peripheral shell of reactive bone. B CT of the

same lesion (arrow).

Fig. 20.02 Aneurysmal bone cyst. MRI of large

destructive lesion of distal femur. Note numerous

fluid-fluid levels.

338 Tumours of undefined neoplastic nature

Fig. 20.03 Aneurysmal bone cyst. A Septa composed of reactive woven bone, fibroblasts, and scattered osteoclast-like giant cells. B So-called 'blue bone" in wall of

the lesion.

Genetics

The most notable genetic feature is the

characteristic rearrangement of the

chromosome 17 short arm {1645}. The

chromosome 17 rearrangements are

often in the form of balanced transloca-

tions, in which material is exchanged

with the long arm of chromosome 16.

However, there are many variations on

this theme, and at least five different

chromosomes can serve as transloca-

tion partners with chromosome 17

{435,938,1645,1909,2281,2311}. The

cytogenetic analyses invariably reveal

normal metaphases along with those

bearing the translocations. Therefore,

the translocations can be assumed to

result from acquired aberrations, arising

in cytogenetically normal precursor

cells. The cytogenetic findings provide

compelling evidence that many aneursy-

mal bone cysts are clonal proliferations,

with activation of a 17p oncogene play-

ing a key role in their tumourigenesis.

The mechanisms of oncogene activation

appear to be heterogeneous, as shown

by the different types of 17p rearrange-

ment, and as evidenced by the absence

of 17p rearrangement in some cyto-

genetically abnormal aneursymal bone

cysts {135,435,938,1645,1909,2281,

2311}. It is also striking that these

varied, but related, cytogenetic abnor-

malities have been reported across the

entire clinicopathological spectrum of

aneursymal bone cysts. Chromosome

16 rearrangement was identified in a

solid variant aneursymal bone cyst,

whereas chromosome 17 rearrangement

was found in an extra-osseous case

{435}. Hence, it appears that there are

generalisable transforming mecha-

nisms, that are utilised irrespective of

histological subtype or site of origin.

Fig. 20.04 Aneurysmal bone cyst of proximal fibula.

The well-defined haemorrhagic multicystic mass

has a prominent solid component in the centre.

Prognostic factors

ABC is a benign potentially locally

recurrent lesion. The recurrence rate fol-

lowing curettage is variable (20-70%).

Spon- taneous regression following

incomplete removal is very unusual.

Rare cases of apparent malignant trans-

formation of ABC have been reported

{1197}.

Aneurysmal bone cyst

339

Simple bone cyst

R.K. Kalil

E.S. Araujo

Definition

An intramedullary, usually unilocular,

bone cyst (cavity) filled with serous or

sero-sanguineous fluid.

Roentgenograms show a metaphysio-

diaphyseal lucency, extending up to

epiphyseal plate, with little or no expan-

sion of bone; marginal sclerosis is

absent or very thin. The cortex is usual-

ly eroded and thin, but is intact unless

pathological fracture has occurred.

There can be partial or complete septa-

tions of the cavity. MRI usually confirms

its fluid content, that can be bloody in

fractured lesions {1328}.

Prognostic factors

Recurrence is reported at 10-20% of

cases, especially in children. Growth

arrest of the affected bone and avascular

necrosis of the head of the femur after

pathological fracture can occur {2022}.

Spontaneous healing after fracture has

been described {52}.

Synonyms

Solitary bone cyst; unicameral bone cyst;

juvenile bone cyst; essential bone cyst.

Epidemiology

Males predominate in a ratio of 3:1.

About 85% of patients are in the first two

decades of life.

Aetiology

Growth defect at the epiphyseal plate

has been postulated, or that a venous

blood flow obstruction causes the sim-

ple cyst {342}.

Sites of involvement

There is a predilection for long bones,

proximal humerus, proximal femur and

proximal tibia accounting for up to 90%

of cases. Pelvis and calcaneus are also

common locations in older patients.

Macroscopy

The cystic cavity is usually filled with

serous or sero-sanguineous fluid. The

inner surface of the cyst shows ridges

separating depressed zones covered

by a layer of thin membrane. Partial

septae may be seen.

The occasionally curetted specimen

consists of fragments of a usually thin,

whitish membrane that may be

attached at one surface to bone

spicules.

Clinical features / Imaging

Simple bone cyst can produce pain and

swelling but, more frequently, patients

present with a pathological fracture.

Fig. 20.06 Simple bone cyst of proximal ulna. A

unilocular cyst contains fibrin clot.

Histopathology

The inner lining and septae of the cyst

consist of connective tissue that can,

occasionally, contain foci of reactive

new bone formation, haemosiderin pig-

ment and scattered giant cells.

Fibrinous deposits are often seen.

Some of these are mineralized, resem-

bling cementum. Occasionally, histo-

logical features of fracture callus may

be prominent. Rare "solidified" cases of

simple bone cyst have been described

in older subjects.

Fig. 20.05 Simple bone cyst of proximal femur. The

lesion does not expand the bone.

Genetics

A highly complex clonal structural

rearrangement involving chromosomes

4, 6, 8, 16, 21 and both chomosomes

12 has been described in a surgically

resected solitary bone cyst in an 11-

year-old boy {2195}.

Fig. 20.07 Simple bone cyst. The lining is usually

inconspicuous and contains scattered spindle

cells and giant cells.

340 Tumours of undefined neoplastic nature

Fibrous dysplasia

G. Siegal

P. Dal Cin

E.S. Araujo

Definition

Fibrous dysplasia (FD) is a benign

medullary fibro-osseous lesion which

may involve one or more bones.

the skull are favoured sites in men

{2154}. In the monostotic form, about

35% of cases involve the head, a sec-

ond 1/3 occur in the femur and tibia, and

an additional 20% in the ribs. In the

polyostotic form, the femur, pelvis, and

tibia are involved in the majority of cases

{890}.

circumscribed of blue-tinged translucent

material {2154}.

Histopathology

The lesion is generally well circum-

scribed and composed of fibrous and

osseous components; which are present

in varying proportions from lesion to

lesion and also within the same lesion.

The fibrous component is composed of

cytologically bland spindle cells with a

low mitotic rate. The osseous component

is comprised of irregular curvilinear tra-

beculae of woven (or rarely lamellar)

bone. Occasionally, the osseous compo-

nent may take the form of rounded

psammomatous or cementum-like bone.

Secondary changes such as foam cells,

Synonyms

Fibrocartilagenous dysplasia, general-

ized fibrocystic disease of bone.

Epidemiology

Fibrous dysplasia occurs in children and

adults world-wide and affects all racial

groups with an equal sex distribution.

The monostotic form is six times more

common than polyostotic fibrous dys-

plasia.

Clinical features / Imaging

Fibrous dysplasia may present in a

monostotic or polyostotic form, and in

the latter case, can be confined to one

extremity or one side of the body or be

diffuse. The polyostotic form often mani-

fests earlier in life than the monostotic

form {890}. The lesion is often asympto-

matic but pain and fractures may be part

of the clinical spectrum {333}. Fibrous

dysplasia may also be associated with

oncogenic osteomalacia {1660}.

The polyostotic form of fibrous dysplasia

is intimately associated with McCune-

Albright syndrome, in which there are

endocrine abnormalities and skin pig-

mentation. There is also a relationship

between fibrous dysplasia and intramus-

cular myxomas (Mazabraud syndrome)

{630}.

Rontgenographic studies often show a

non-aggressive geographic lesion with a

ground glass matrix. There is generally

no soft-tissue extension, and a

periosteal reaction is not seen unless

there is a complicating fracture. CT

scans and MRI further delineate these

features and better define the extent

{422,1035,2118}.

Sites of involvement

The gnathic (jaw) bones are the most

common site of involvement in surgical

series (because they are often sympto-

matic) {1596}. In women, long bones are

more often involved, whereas ribs and

Fig. 20.09 CT of skull with fibrous dysplasia. In flat

bones the process is often expansile.

Aetiology

Activating mutations of the G proteins

have been identified in both the mono-

stotic and polyostotic forms and may be

aetiologically important.

Fig. 20.08 X-ray of a polyostotic form of fibrous dys-

plasia. There is a well defined lucency with scle-

rotic margins.

Macroscopy

The bone is often expanded and the

lesional tissue has a tan grey colour with

a firm-to-gritty consistency. There may

be cysts, which may contain some yel-

low-tinged fluid {1948}. When cartilage

is present, it often stands out as sharply

Fig. 20.10 Fibrous dysplasia with gross cartilaginous

components.

Fibrous dysplasia

341

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