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CHAPTER 5

Pericytic (Perivascular) Tumours

Pericytic / perivascular neoplasms have traditionally been domi-

nated by haemangiopericytoma. However, it is now recognized

that the latter diagnostic category subsumes a wide variety of

tumour types which share the presence of thin-walled branch-

ing blood vessels. If such lesions are otherwise classified, there

remains only a small group of spindle cell lesions designated

as haemangiopericytoma, although they have no evident rela-

tionship to pericytes, and may be more closely related to soli-

tary fibrous tumour (see Chapter 2).

The lesions now remaining in this pericytic / perivascular cate-

gory all show evidence of differentiation towards myoid / con-

tractile perivascular cells and all share the characteristic ten-

dency to grow in a circumferential perivascular fashion.

Currently, the term ‘myopericytoma’ is preferred to avoid confu-

sion with the ill defined former terminology.

Important advances have been made in predicting biological

potential of glomus tumours and in understanding the close

relationship between myopericytoma, myofibroma / myofibro-

matosis, and so-called infantile haemangiopericytoma, which

essentially form a single morphological continuum. Their myoid

nature and shared features with angioleiomyoma explain their

more logical alignment with smooth muscle tumours rather than

vascular tumours in this new classification.

Sinonasal haemangiopericytoma, which appears to be a truly

pericytic lesion, is described in the Respiratory System volume.

Glomus tumours

A.L. Folpe

Definition

Glomus tumours are mesenchymal neo-

plasms composed of cells that closely

resemble the modified smooth muscle

cells of the normal glomus body.

Histopathology

Typical glomus tumours

Typical glomus tumours are subcatego-

rized as "solid glomus tumour", "gloman-

gioma", and "glomangiomyoma" depend-

ing on the relative prominence of glomus

cells, vascular structures and smooth

muscle. Glomus cells are small, uniform,

rounded cells with a centrally placed,

round nucleus and amphophilic to lightly

eosinophilic cytoplasm. Each cell is sur-

rounded by basal lamina, seen best on

PAS or toluidine blue histochemical

stains. Occasionally cases show onco-

cytic {1967} or epithelioid change

{1737}.

Solid glomus tumours are the most com-

mon variant, comprising approximately

75% of cases {2242}. They are com-

posed of nests of glomus cells surround-

ing capillary sized vessels. The stroma

may show hyalinization or myxoid

change. Small cuffs of glomus cells are

often seen around small vessels located

outside of the main mass. Gloman-

giomas, comprising approximately 20%

of glomus tumours, are characterized by

dilated veins surrounded by small clus-

ters of glomus cells. Glomangiomas are

the most common type of glomus tumour

in patients with multiple or familial

lesions. Glomangiomyomas, the least

common subtype of typical glomus

tumour, are characterized by an overall

architecture similar to solid glomus

tumour or glomangioma and by a transi-

tion from typical glomus cells to elongat-

ed cells resembling mature smooth mus-

cle. In some glomus tumours a branch-

ing, haemangiopericytoma-like vascula-

ture is present and such cases have

been designated "glomangiopericytoma"

{825}.

tumour investing the vascular walls. It is

benign despite its infiltrative growth.

Symplastic glomus tumours

Symplastic glomus tumours show strik-

ing nuclear atypia in the absence of any

other worrisome feature (e.g., large size,

deep location, mitotic activity, necrosis)

{697}. The marked nuclear atypia that

characterizes these tumours is believed

to be a degenerative phenomenon. All

cases reported to date have behaved in

a benign fashion.

ICD-O codes

Glomus tumour

8711/0

Glomus tumours of uncertain

malignant potential

8711/1

Malignant glomus tumour

8711/3

Epidemiology

Glomus tumours are rare, accounting

for less than 2% of soft tissue tumours

{1946}. Multiple lesions may be seen in

close to 10% of patients. Malignant

glomus tumours are exceedingly rare,

comprising less than 1% of glomus

tumours {697}.

Glomus tumours typically occur in

young adults but may occur at any age.

No sex predilection is seen, except in

subungual lesions, which are far more

common in women {2079,2177}.

Malignant glomus tumours

(glomangiosarcomas) and glomus

tumours of uncertain malignant potential

Histologically malignant glomus

tumours are exceedingly rare and clini-

cally malignant ones (e.g., metastatic)

rarer yet. Prior to 2000, fewer than 20

histologically malignant and 2 clinically

malignant tumours had been reported

{21,54,247,823,885,952,953,1575,

2219,2220, 2255}. Criteria for the diag-

nosis of malignancy in glomus tumours

were only recently elaborated {697}.

The diagnosis of "malignant glomus

tumour" should be reserved for tumours

showing: 1) Size >2 cm and subfascial

or visceral location; 2) Atypical mitotic

figures; or 3) Marked nuclear atypia

and any level of mitotic activity. These

features frequently co-vary in a given

case. A component of pre-existing

benign-appearing glomus tumour is

often but not always present. There are

two types of malignant glomus tumour.

Sites of involvement

The vast majority of glomus tumours

occur in the distal extremities, particular-

ly the subungual region, the hand, the

wrist and the foot {2246}. Rare tumours

have however been reported in almost

every location, including the stomach

{885}, penis {1132}, mediastinum {952},

nerve {293}, bone {1815} and lung {751}.

Glomus tumours almost always occur in

the skin or superficial soft tissues,

although rare cases occur in deep soft

tissue or viscera. Malignant glomus

tumours are usually deeply seated, but

may be cutaneous {697}.

Clinical features

Cutaneous glomus tumours are typically

small (<1 cm), red-blue nodules that are

often associated with a long history of

pain, particularly with exposure to cold

or minor tactile stimulation.

Deeply seated or visceral glomus

tumours may have either no associated

symptoms or symptoms referable to the

involved organ.

Glomangiomatosis

Glomangiomatosis is an extremely rare

variant of glomus tumour with an overall

architectural resemblance to diffuse

angiomatosis (see page 161) {697, 823,

1294}. Glomangiomatosis is distin-

guished from angiomatosis by the pres-

ence of multiple nodules of solid glomus

Fig. 5.01 Glomus tumour. Note the typical rounded

cytomorphology and well defined cell membranes.

136 Pericytic (perivascular) tumours

Fig. 5.02 Glomangioma. The lesion is composed of

dilated vascular spaces, the walls of which contain

several layers of glomus cells.

Fig. 5.03 Glomangioma, composed of dilated vascu-

lar spaces, the walls of which contain several layers

of glomus cells.

Fig. 5.04 Glomus tumour. A Tumour cells show con-

sistently strong immunoreactivity for smooth muscle

actin. B Ultrastructure showing prominent external

lamina, pinocytotic vesicles and intracytoplasmic

actin microfilaments.

In the first type, the malignant com-

ponent resembles a leiomyosarcoma or

fibrosarcoma. In the second type, the

malignant component retains an overall

architectural similarity to benign glomus

tumour and consists of sheets of highly

malignant appearing round cells.

Immunohistochemical demonstration of

smooth muscle actin and pericellular

type IV collagen is required for the

diagnosis of this second type of

malignant glomus tumour, in the ab-

sence of a clear-cut benign precursor.

Malignant glomus tumours are highly

aggressive with metastases in appro-

ximately 40% of cases, resulting in the

death of the patient {697}. Glomus

tumours not fulfilling criteria for ma-

lignancy, but having at least one

atypical feature other than nuclear

pleomorphism should be diagnosed as

"glomus tumours of uncertain malignant

potential".

bundles of thin actin-like filaments with

dense bodies and occasional attach-

ments plaques to the cytoplasmic mem-

brane and prominent external lamina

{1449}.

Immunohistochemistry

Glomus tumours of all types typically

express smooth muscle actin and have

abundant pericellular type IV collagen

production. H-caldesmon is also posi-

tive. Other markers, including desmin,

CD34, cytokeratin and S100 protein are

usually negative {697}.

Genetics

Multiple familial glomus tumours appear

to have an autosomal dominant pattern

of inheritance {164,884,1363}. An asso-

ciation between subungual glomus

tumours and neurofibromatosis type I

has been reported {1109,1602,1867}.

The gene for multiple inherited glomus

tumours has been linked to chromo-

some 1p21-22 {229,297}. The genetic

events underlying sporadic glomus

tumours are not known.

Ultrastructure

Ultrastructurally glomus cells have short

interdigitating cytoplasmic processes,

Fig. 5.06 A Malignant glomus tumour, spindle cell type. B Malignant glomus tumour, round cell type. Note the

brisk mitotic activity.

Fig. 5.05 Symplastic glomus tumour with prominent

nuclear atypia but without mitotic activity.

Glomus tumours

137

Myopericytoma

M.E. McMenamin

Definition

Myopericytoma is a benign, generally

subcutaneous tumour that is composed

of oval-to-spindle shaped myoid appear-

ing cells with a striking tendency for con-

centric perivascular growth. It is believed

that the lesional cells show apparent dif-

ferentiation towards perivascular myoid

cells or myopericytes. Myopericytoma

forms a morphological continuum with

myofibroma, angioleiomyoma and so-

called infantile haemangiopericytoma.

Histopathology

Myopericytomas are unencapsulated and

most lesions are fairly well circumscribed.

Lesions are composed of relatively

monomorphic oval-to-spindle shaped

myoid appearing cells that show striking

multilayered concentric growth around

lesional blood vessels. The cells have

eosinophilic or amphophilic cytoplasm.

Lesions can be solidly cellular; however

some cases have prominent myxoid stro-

ma. In occasional cases, the spindle cells

fall apart in the intervascular regions. In

many cases, blood vessels outside the

ICD-O code

8713/1

Synonyms

In the past, myopericytoma may have

been diagnosed as a solitary myofibro-

ma or "haemangiopericytoma."

Epidemiology

Myopericytoma arises most commonly in

mid adulthood; however, lesions can

arise at any age. Familial cases have not

been reported.

Sites of involvement

Myopericytoma generally arises in sub-

cutaneous tissue. There is a predilection

for lesions to involve the distal extremi-

ties; however, tumours can also arise at

other sites, including the proximal

extremities and neck. It is likely that a

wider site distribution will be described

with increased recognition of this tumour.

Clinical features

Myopericytoma generally presents as a

painless, slow-growing subcutaneous

nodule that can be present for years.

Some lesions are painful. Myopericytoma

most commonly arises as a solitary

lesion but multiple lesions are not infre-

quent. Multiple lesions generally arise

metachronously and usually involve a

particular anatomic region such as a

foot.

Macroscopy

Myopericytoma tends to be a well cir-

cumscribed nodule measuring less than

2 cm in diameter.

Fig. 5.07 Myopericytoma. A Typical proliferation of tumour cells around blood vessels at the periphery of this

poorly circumscribed example. B Prominent gaping thin-walled blood vessels (left) and formation of whorls of

spindle cells.

138 Pericytic (perivascular) tumours

lesion also show concentric perivascular

proliferation of spindle cells. Lesional

blood vessels tend to be numerous and

can be variable in size. In some cases,

numerous thin walled branching or gap-

ing blood vessels are present. Fasicular

or whorled arrangements of spindle cells

with abundant eosinophilic cytoplasm,

embedded in myxoid stroma, are present

in some cases. These areas are similar to

the myoid whorls of myofibromatosis/

myofibroma and invagination or bulging of

these areas into the lumina of lesional

blood vessels is frequently seen.

Subendothelial proliferation of lesional

cells in vessel walls is frequently seen

and, indeed, myopericytoma can be

located entirely within the lumen of a vein.

Some myopericytomas have a compo-

nent of cells with glomus-type features

including cuboidal shape, distinct cell

borders, clear to eosinophilic cytoplasm

and central round nuclei and the term glo-

mangiopericytoma can be used in such

cases. In reality a spectrum of lesions

exists that includes myofibromatosis,

myofibroma, infantile haemangiopericy-

toma, glomangiopericytoma and myoper-

icytoma {295,825}. Rarely, lesions show

marked hyalinization, cystic change or

focal metaplastic bone. Mitoses are not

conspicuous (generally much less than

1/10 HPF). Coagulative necrosis has been

described in a glomangiopericytoma;

however, this appears to be a very unusu-

al finding {825}.

Immunophenotype

The spindle cells in myopericytomas are

positive for smooth muscle actin (SMA).

SMA staining is generally diffusely posi-

tive, but can be only focally positive, gen-

erally in a perivascular distribution.

Fig. 5.08 Myopericytoma. A Concentric perivascular growth pattern and foci of myxoid stroma. B A multilayered

concentric proliferation of spindle cells with myoid features around blood vessels.

Occasional cases are focally desmin

positive {825}. Focal CD34 staining by

lesional cells occurs in some cases.

Lesional cells are negative for S100 pro-

tein and most cases are negative for

cytokeratin.

Fig. 5.09 Myopericytoma. Marked immunoreactivity

for smooth muscle actin accentuates the perivascu-

lar growth pattern.

Prognostic factors

Most myopericytomas do not recur fol-

lowing excision. Recurrence may be

related to poor circumscription of a

lesion. Sometimes it is difficult to know

whether a myopericytoma has recurred

or whether a new lesion has developed in

the same anatomic area. Very rare malig-

nant myopericytomas exist {1383}.

Fig. 5.10 Myopericytoma. A whorl of spindle cells in

myxoid stroma bulges into the lumen of a blood ves-

sel reminiscent of myofibromatosis / myofibroma.

Myopericytoma

139

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