The skull bones
are affected by lesions similar to those seen in the other bones,
such as benign or malignant neoplasms or metastatic deposits,
congenital dysplasias, metabolic disorders, and hemopoietic
disorders. The vault of the skull is made up of membrane bones
whereas the base is of cartilaginous origin.
It has been
reported that the primary skull tumors account for 0.8% of all bone
tumors. The vault is made up of membrane bones whereas the base is
of cartilaginous origin. This influences the pathology. Lesions that
are primarily intracranial may involve the skull secondarily, and
similarly, skull tumors can spread intracranialy.
local pain are the usual presenting symptoms. Associated
neurological deficit suggests intracranial extension.
symptoms by expansion of the skull or compression of the adjacent
brain or venous sinuses.
lesions can invade or compress the cranial nerves. Headache and/or
focal bony pain may result. When cerebral venous thrombosis occurs
secondary to compression or invasion, the abrupt or insidious onset
of headache is related to elevated intracranial pressure.
The site of skull
base lesions can often be localized by the cranial nerve deficits.
There are five clinical syndromes:
syndrome is characterized by progressive supraorbital pain over
the affected eye and visual blurring, followed by diplopia. On
examination, there is proptosis of the affected eye and external
ophthalmoplegia; there is variable numbness in the first division of
the trigeminal nerve and pre-orbital swelling.
or cavernous sinus metastasis syndromes are characterized by a
severe, unilateral frontal headache and diplopia. There is paresis
of either or both of the oculomotor and abducens nerves, numbness in
the first division of the trigeminal nerve, and possibly papilledema.
There is no proptosis.
complaints in those with middle fossa (gasserian ganglion)
syndrome are numbness, paresthesias, or pain in the area innervated
by the second or third division of the trigeminal nerve. Headache
the jugular foramen produces hoarseness or dysphagia and
often retroauricular pain. Examination reveals evidence of
glossopharyngeal, vagus, and accessory nerve dysfunction.
patients with the occipital condyle syndrome present with
severe unilateral occipital pain, exacerbated by neck flexion and
associated with neck stiffness, pain over the occipital area, and
unilateral hypoglossal nerve paralysis.
scan has mostly replaced plain x-rays. It provides accurate
information regarding the involvement of the skull bones as well as
the intracranial and extracranial soft tissues. Contrast studies
assess the vascularity and the involvement of dural venous sinuses.
scan provides better delineation of soft tissue involvement. As
compact cortical bone lacks in unbound protons, the inner and outer
tables appear as a signal void. The diploe has abundant fat and
hence images well. It is specially useful in skull base lesions
Contrast-enhanced MRI of the skull base that can detect soft tissue
abnormalities and provide excellent visualization of the cavernous
sinus and cranial nerves.
angiography has limited indications.
radiotherapy, and chemotherapy are often used in combination as in
other bone tumors.
depends on the suspected nature and the site as well as intracranial
involvement. Needle biopsy is a simple out patient procedure and may
provide a clue on pathology. Primary lesions, ideally, are excised
completely whenever possible. Cranioplasty may be done at the same
sitting or at a later stage. Skull base lesions may need special
exposures and involvement of plastic and ENT surgeons.
complete excision is not possible, surgical palliation may be
considered to avert neurological or life-threatening events,
especially in patients whose prognosis is uncertain. Surgical
debulking of a mass lesion may allow for more effective chemotherapy
and radiation therapy.
therapy, either curative or palliative, is the mainstay for
malignant tumors. Multiple small fractionated doses per day spread
out over a longer time, is more effective with less damage to normal
structures. Generally, the required dose is 55 Gray or 5500 rads in
30 fractions over six weeks utilizing megavoltage photon radiation.
There is 1% risk of delayed sarcoma in the irradiated bone. Higher
energy photon or electron beam therapy is ideal and can be tailored
to the tumor volume by computerized techniques.
alone is useful in a few, such as, lymphomas. Currently, it is used
as an adjuvant to other forms of therapy and as a palliative
a) Benign skull
commonest (about 30%). They arise from membranous bone and
proliferate into dense cortical or spongy cancellous bone. The
frontal and mastoid air cells are common sites. These slow growing
tumors form an outward excrescence which is hard and painless and
are usually noted while combing the hair. A compact osteoma may
become hard like ivory. The attachment to the skull may be narrow
or broad. Rarely, an osteoma may extend intracranially and cause
In plain X-rays,
an osteoma is seen as a solid homogenous bony shadow. There are no
increased vascular channels. Tangential projections reveal the base
and the absence of involvement of the diploid and inner table. When
the inner table is involved, differentiation from a meningioma
becomes necessary. CT gives the precise diagnosis. Myltiple osteoma
of the calvaria and mandible with soft tissue tumors of the skin and
colonic polyposis form the triad of Gardner’s syndrome.
Microscopically, the tumor is a nucleus of osteoid tissue in a
background of osteoblastic connective tissue and is completely
enclosed by reactive bone. Histological differentiation from
fibrous dysplasia is difficult: but the presence of smooth,
homogeneous and sharply defined sclerotic nodules is unusual 0in
surgically curable. The indications for removal are rapid growth,
pain, obstruction to sinus out lets and noticeable deformity. Small
osteomas of the outer table may be resected easily without
destruction of the inner table. As these lesions are very hard, it
is wiser to remove them by cutting around their base through the
cancellous tissue. A large lesion needs removal of the entire bone
as a flap and the defect is closed by cranioplasty. After excising
the bone flap. The osteoma can be excised from the flap and the flap
can be autclaved and used to close the defect primarily.
constitute about seven per cent of all skull tumors. About two
thirds of haemangiomas of bone occur in the skull or the vertebral
column. They arise from the vascular elements of the diploe, mainly
in the vault of the skull and to a lesser extent in the roof of
orbit or petrous temporal bone. They are slow growing and may reach
a large size. They are painless and the presence of a swelling is
the chief complaint. The swelling is hard, but may be soft in some
places. The skull is involved by erosion and the margins are
imperceptible. Dilated veins may be present. In haemangiomas of the
orbit, proptosis, blindless or extra ocular palsies may be seen.
Haemangioma of the petrous bone may present with deafness and
cranial nerve palsies.
The plain X-rays
show a swelling with a typical honeycombed or sunburst appearance.
The diploe is enlarged and both tables of the skull bulge, outer
more than the inner. Rarely, intracranial extension is seen. The
trabeculae are seen vertically oriented. The edges are well defined
and a thin margin of bony condensation may be evident. CT images
with “bone window” show the hypodense matrix with discrete,
thickened, sclerotic and widely separated trabeculae. Despite the
vascular nature of the lesion, contrast enhancement is an exception
rather than the rule. Carotid angiography shows enlargement of the
external carotid artery branches. Rarely, there may be an internal
carotid supply to these tumors.
usually by enbloc excision or wide curettage. The tumor appears as
a blue domed hard mass under the pericranium. Sometimes the dural
surface may bleed profusely in which case circumferential incision
of the dura and resuturing will help. Radiotherapy is advisable in
situations where excision is not feasible. Doses up to 30 Gy(3000
rads), in three weeks, may be required.
Giant cell tumors
arise from the cartilaginous bone in the sphenoid, mastoid or
occipital areas. They are extremely rare in the bones of the vault,
as osteoclasts are not usually present in membrane bones. Their
pathogenesis is unknown, although trauma and hemorrhage may precede
the skull presents as a painless bony swelling and radiographs show
evidence of rarefaction or destruction of bone. Excision is the
treatment of choice; but it is often incomplete and needs
supplementary radiotherapy to ensure freedom from recurrence.
Occasionally, malignant changes have been reported after surgery and
of developmental origin are derived from epithelial cell rests
ectopically included in the bone during development. They are
commonly seen in or near the midline in the vertex, the frontal or
occipital regions or in the temporal bone. However, they may occur
anywhere in the clavarium. They originate in the diploe and enlarge
in the both directions expanding and thinning both the tables by
continuous growth pressure. The bone at the edge of the lesion gets
sclerosed. The lesion may break through the egg shell thin tables
and expand under the scalp or extradurally. The swelling under the
scalp is firm, rubbery and non-tender. Sometimes a tract may extend
through the inner table and dura to end in an intradural lesion. A
lesion in the midline especially over the torcula may involve the
venous sinuses. Very large intracranial extensions may exist with
surprisingly normal intracranial pressure and with no neurological
deficits. These are described as giant intradiploic epidermoids.
The larger lesions, especially epidermoids, tend to get infected and
osteomyelitis may result.
show a clear cut area of radio-lucency in the skull sclerosed
margins resembling an emissary foramen. Tangential views show
expansion of the tables. CT accurately delineates the bony defect
and the size, location and extension of the soft tissue mass outside
and inside the skull and dura. The lesion appears hypodense
relative to the adjacent brain, due to the contained keratinized
debris and cholesterol. They do not enhance with contrast, but
adjacent compressed brain shows marginal enhancement. On MR these
lesions appear hyperintense in T2 weighted images and most often
hypointense in T1weighted images.
Treatment is by
surgery. Pure extracranial lesions can be excised enbloc. A careful
search must be made for any intradiploic or intracranial extension
along a thin track which, if present, needs to be excised. While
dealing with midline lesions the surgeon must be prepared to do an
extensive craniotomy and venous sinus repair if necessary.
arise mainly in the cartilaginous bones of the base of the skull.
They commonly occur between the ages of 20 and 40 years. The common
sites are the paranasal sinuses and the spheno-ethmoidal and spheno-occipital
extended into the sellar or parasellar region, producing visual and
ocular nerve palsies or endocrine dysfunction. The posterior lesions
may compress the brainstem and involve the lower cranial nerves.
Radiographically, a chondroma appears a lytic lesion at the base of
the skull with fairly sharp margins. Areas of stippled calcification
maybe seen in more than 60 per cent. CT reveals well marginated
bone destruction and an associated homogenous, isodense and
lobulated soft tissue mass with interspersed calcification.
Contrast enhancement is infrequent and when present is minimal.
changes occur in one to two per cent of these tumors, more
frequently in individuals with Mafucci’s syndrome (multiple
enchondromas and multiple subcutaneous hemangiomas). Rapid growth
indicates a malignant change. Histologically, malignancy is deduced
by the presence of atypical cartilage cell nuclei in the actively
growing peripheral portions of the neoplasm. The treatment of a
chondroma is total removal wherever possible. Most often only
partial removal is possible, especially at the skull base.
Decompression of neural structures by such partial removal is often
is a multiloculated expanding cystic tumor with a rich vascular
network in the walls. The encircling inner and outer tables are
eroded to form thin bony shells. Some cysts show a central core of
hemangioma and repeated hemorrhage may be the cause of the cystic
expansion of the skull tables. These lesions may either becomes
symptomatic or enlarge during pregnancy. On CT, the contents of the
cyst may be of the fluid. The superficial temporal and middle
meningeal arteries supply the tumor and this is made out well on
selective external carotid angiography.
fibromas (benign osteoblastoma)
are a rare solitary, vascular tumor predominantly osteolytic in
character with varying degree of calcification and new bone
formation. Treatment is local excision.
are seen occasionally in the base of the skull, but rarely in the
vault. Depending on the site of origin, they produce signs of
pressure on the optic nerves, the pituitary, the hypothalamus, the
brainstem and other cranial nerves. Radio logically, islands of
erosion with normal bone in between are seen. Local excision and
post operative radiotherapy is the usual practice.
rare, usually in adults, as a malignant transformation in a benign
chondroma. The common site is the base of skull, in and around the
sella, CP angle, or the fronto-ethomoidal sinuses. They grow for a
long time and produce pain, deformity, and cranial nerve palsies. CT
reveals an irregular destructive process with a homogenous,
hyperdense, and enhancing soft tissue mass. Radical resection and
radiotherapy is the traditional treatment. They are locally invasive
and tend to recur.
are rare; it occurs usually in the young and in the vault.
Occasionally, it occurs as a late complication following
radiotherapy. They grow rapidly and metastasize to the lungs and
other bones. CT shows an enhancing irregular, heterogenous
extradural mass with prominent new bone formation. Radical excision
and radiotherapy is recommended. Adjuvant chemotherapy helps.
from the periosteum of the skull or the dura. They are rapidly
growing and painful. X-rays show thinning of the outer table with
irregular margins and an overlying soft tissue mass. Radical
excision and post–op radiotherapy is advised. Chemotherapy has no
are slow growing, locally invasive and of embryonal origin from the
remnants of the chorda dorsalis. The smaller ones are pedunculated,
the larger ones are diffuse. The usual sites are at the skull-base,
in the sella, the clivus, and the nasopharynx. The sixth nerve is
commonly affected. Brainstem compression occurs later. CT and MRI
show a soft tissue mass in the midline with bone destruction.
Occasionally (10%) there may be a sclerotic response. Extended skull
base approaches may be needed for satisfactory excision. Post–op
radiotherapy is advised.
rarer tumors, such as, reticulum cell sarcoma, angiosarcoma,
malignant fibrous histiocytoma can occur. The diagnosis is usually
made on histology. Wide excision and radiotherapy is advised.
metastases are usually from the breast, the lungs, the prostate,
the thyroid, and the kidney. Though metastases can affect any
part of the skull, vault is the common site. They are usually
osteolytic, except when the primary is from the prostate, when
it is osteoblastic. Radiologically they appear as multiple,
poorly marginated areas of slightly increased density.
Occasionally in some cases of breast cancer, the skull
metastases may appear as mixed lucent and sclerotic areas. Plain
xrays are positive in 60% of cases and CT in 85%. Extradural and
scalp extension may show as areas of contrast enhancement.
Isotope scans are more sensitive. Biopsy may be needed to
confirm the lesion. Treatment is correlated with that of the
of bone are a common feature in disseminated lymphomas and occur
in 10-15% in Hodgkin’s and 7-25% in non Hodgkin’s. The more
aggressive lymphosarcoma and reticulum sarcoma rarely involve
the skull. Treatment is local radiotherapy and chemotherapy.
appear as ill-defined areas of rarefaction with peripheral new
bone formation similar to neuroblastoma. Low dose radiotherapy
and chemotherapy of the systemic disease is recommended.
affects the males more commonly between 40-60 years of age.
Skull x-rays show multiple punched out areas of bone
destruction. Biopsy or bone marrow biopsy may be needed to
confirm. They are treated with chemotherapy. Occasional solitary
plasmocytomas are treated with radiotherapy.
is a common tumor of childhood. Skull metastases often precede
the detection of the primary adrenal tumor. Diffuse nodular
lucencies are seen radiologically. They are highly vascular and
lift up the periosteum, producing radial bone speculation
extending into the soft tissues. The dura often resist the
spread; however, occasionally, an intratumoral hemorrhage may
rupture into the brain parenchyma. Spontaneous resolution into a
more benign form has been reported; skull metastasis suggest a
poor prognosis. Local radiotherapy and systemic chemotherapy is
the treatment of choice
Skull metastases from Ca.
are often multicentric in origin involving the tibia, ribs, and
vertebrae and rarely seen as a primary skull lesion. Local
radiotherapy and chemotherapy is recommended.
involvement by direct extension:
may produce varying degrees of incidental bony changes in the
overlying skull and may also invade the skull bone itself and
may break through the outer table to present as a subcutaneous
swelling. The involved bone is considerably vascular with
tortuous arterial and large venous channels. The bony changes
may resemble those of fibrous dysplasia. Sometimes, they remain
entirely intra-diploic, expanding the two tables resulting in a
doughnut like lesion. Occasionally, there may be bone
destruction similar to that of a metastasis.
Nasopharyngeal tumors usually become symptomatic long
before the skull involvement. Angiofibroma and squamous cell
pappilloma are the common ones. Marked intracranial extension
may require combined approach with ENT surgeons. The malignant
tumors of the nasopharynx and the paranasal sinuses usually
present with intracranial involvement and are treated with
radiotherapy following biopsy.
jugulare is discussed
Conditions simulating skull tumors:
changes appear radiologically long after the onset of clinical
signs and symptoms. Multiple nodular lucent areas appear in the
outer table or diploe. Later they condense into a large defect
with scalp edema (Pott’s puffy tumor). Poorly defined sclerosis
occurs at the edges of the bone with practically no
subperiosteaL new bone or sequestrum formation.
as complication of growing fracture is children may mimic a
tumor radiologically as a lucent area with scalloped marigins
and a soft tissue shadow outside the skull. Occasionally, it may
be in between the tables producing intraosseous cyst.
in the new born, following forceps delivery, may produce a soft
tissue shadow radiologically. It is commonly seen in the parietal
bone limited by sutures and mimics a tumor. Calcific edges
gradulally project into the soft tissues of the scalp, resulting in
a shell like calcification. Rarely, a deformity persists.
(osteitis deformans) is multicentric involving pelvis, the femora,
the vertebrae, and more commonly the skull. Men are more frequently
involved. It starts as a diffuse mottled thickening in the frontal
or occipital area as irregular patches or lysis which give the
appearance of a geographical skull radiologically. Later, patchy
sclerosis develops. Deafness and blindness due to foraminal
involvement may occur. Except for neural decompression, there is no
specific treatment. Sarcomatous change is infrequent.
rarely involves the skull. It is seen as multiple punched out areas
shows an irregular area of of rarefaction with no sclerosis in
skull radiologically. Complete excision and small dose radiation
(10Gy), is curative. The multiple recurrent type is seen n
children, often involving the frontal bone and spreads
extensively showing clear cut but irregular edges described as ‘
map like’. The facial bones and paranasal sinuses eventually get
invoved. Local radiation following biopsy. And chemotherapy is
is a benign disorder of bone commonly seen in the young. Normal
osteoid is replaced with connective tissue with varying osseous
metaplasia. The cystic type affects the vault, and
type involves the base.vault, the
scleothe sclerotic type involves the base. The mixed
type is rare. There is need for any specific treatment, but for
decompression if there is neural compression. Sarcomatous change
occurs in any of the paranasal sinuses, commonly in the frontal,
due to outflow obstruction in the sinus cavity. The walls bulge
and may burst through the dura. A sphenoidal lesion may erode
the optic foramen. The floor of the sella may bulge upwards.
Ethmoidal lesion may produce proptosis. Complete excision with
all the sinus lining is advised.
is a congenital skull defect, containing abnormal emissary veins
which connect an intracranial venous sinus, commonly the
superior sagittal sinus in the frontal region with a cluster of
veins or a venous angioma in the extracranial space. Typically,
the veins bulge as a swelling in the recumbent posture and
disappear in the erect posture.