Download CT AND MRI FEATURES OF THE SKULL BASE GLOMUS TUMOUR

Ettaby et al.
Alexandria Bulletin
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CT AND MRI FEATURES OF THE SKULL BASE GLOMUS TUMOUR
Ashraf Nagiub Ettaby*, Hesham Taha Kotb*, Hani Farouk Elgarem**
and Sherif Abdel Monem Mohamed Shama*
Radiodiagnosis* and Otorhinolaryngology** Departments,
Faculty of Medicine, Alexandria University
ABSTRACT
Background: The glomus tumor has been the focal point, owing to its precarious location, around which the field
of neurotologic skull base surgery has evolved. Surgery has emerged as the undisputed definitive management
preference for glomus tumors. This innovative surgery has been predominantly stimulated by developments in the
ability to diagnose and delineate type and extent of disease radiologically. Data for any neurotologic skull base
surgical plan must include determination of tumor type, size, and extent as well as evaluation for synchronous
lesions or histochemical associated phenomenon; assessment of major vascular involvement and assessment of
intracranial collateral circulation together with assessment for intracranial extension. None of these data essential
to surgical planning are safely derivable from the clinical evaluation. The diagnostic mainstay of glomus tumor
diagnosis is medical imaging.
Purpose: We aimed in this study to evaluate the diagnostic performance of the cross sectional imaging including
both CT and MRI in diagnosis of different types of the glomus tumors.
Patients and Methods: Sixteen patients with glomus tumor were studied, collected during two-year-duration:
Starting from July 2003 till July 2005. None of these patients had bilateral involvement. Ten female and 6 male
patients were encountered. Their ages ranged from 33 to 68 years. The glomus family had 4 patients of glomus
tympanicum, 8 patients of glomus jugulo-tympanicum and another 4 patients of glomus jugulare. The CT and MRI
findings of each type of the glomus tumour were detected and described as well as compared with the previous
findings published in the literature.
Results: On CT, The bone changes with glomus tumors were irregular, and the margins were indistinct and may
be described as "moth-eaten. On MRI All tumors showed intense enhancement after IV contrast administration but
the characteristic salt-and-pepper pattern could be detected only in relatively large glomus jugulare and jugulotympanicum and it was not clearly seen in small cases of glomus tympanicum. Only two cases of huge glomus
jugulare showed the dropout effect.
Conclusion: We concluded that MRI and CT must not be considered exclusive, and when diagnostically indicated,
each may be employed to supplement the other. The different types of glomus are relatively consistent in location,
configuration, CT density, MR intensity and enhancement patterns. If one analyzes each lesion systematically,
takes into consideration the clinical information, and avoids the traps set by the occasional lesions intruding into
the same anatomical territories, a correct preoperative diagnosis can be reached in a large percentage of the
cases.
INTRODUCTION
Skull base tumors are a group of tumors that grow
along different areas under the brain or within the
bottom part of the skull. Although most glomus
tumors are benign, due to their location, which is
close to the brain and various nerves, their growth
can cause significant problems. The most common
types of these tumors include glomus tumors, facial
neuromas, schwannomas, chordomas, chondrosarcomas, and metastatic tumors, including head and
neck cancers that spread to the skull base. Glomus
tumors are also known as temporal bone paragangliomas.(1) The paraganglia are small aggregates
of cells derived from embryonic neuroepithelium
that is distributed throughout the body. These tumors
are closely associated with the sympathetic nervous
system. Glomus tumors represent chemoreceptors in
a diffuse neuroendocrine system and are composed
of amine precursor uptake and decarboxylation
cells. Most of the paragangliomas of the skull
base are found along the course of the tympanic
branch of cranial nerve IX, in the adventitia of
the jugular bulb, in the tympanic canaliculus, or
Bull. Alex. Fac. Med. 42 No.2, 2006.
along the lesser petrosal nerve. A glomus tumor
confined only to the middle ear is a glomus
tympanicum. One involving the jugular bulb and
cranial base is a glomus jugulare. These tumors are
slow growing hypervascular tumors that usually
occur in the temporal bone and gradually can
destroy the inner ear and other bone around them to
involve the carotid artery (the artery that takes the
blood to the brain) and even grow into the brain
Patients usually present with gradual hearing loss,
unilateral pulsatile tinnitus, and lower cranial nerve
palsies. Approximately 1-3% of gangliogliomas
produce catecholamines, and they may be locally
invasive but rarely metastasize.(1,2,3)
The glomus tumor has been the focal point,
owing to its precarious location, around which the
field of neurotologic skull base surgery has evolved.
The past 50 years have seen the development of
microsurgical techniques, advances in anesthesia
and reconstructive capabilities to a degree which
currently allow the heretofore unresectable to be
reliably considered resectable. Surgery has emerged
as the undisputed definitive management preference
for glomus tumors. This innovative surgery has been
ISSN 1110-0834
336
SKULL BASE glomus tumour.
predominantly stimulated by developments in the
ability to diagnose and delineate type and extent of
disease radiologically. Consistently outpaced by
diagnostic progress in the past, surgery has finally
evolved to a point of compatibility with the ability to
image these tumors. It is this concept of informed
pretreatment investigation. The ultimate treatment of
the glomus tumor depends on tumor type and extent.
Each lesion is considered unique. Data for any
neurotologic skull base surgical plan must include:
1. determination of tumor type, size, and extent; 2.
evaluation for synchronous lesions or histochemical
associated phenomenon; 3. assessment of major
vascular involvement; 4. assessment of intracranial
collateral circulation; 5. assessment of intracranial
extension. Most objectives are attainable by the
identification of a soft-tissue mass and/or its
associated bone destruction. Initial-phase assessment
seeks to differentiate tympanicum from jugulare
lesions. Disease extent is then assessed. None of
these data essential to surgical planning are safely
derivable from the clinical evaluation, i.e., the
patient history and physical examination. The
diagnostic mainstay of glomus tumor diagnosis is
medical imaging.(4-8)
This study was designed to evaluate the
diagnostic performance of the cross sectional
imaging including both CT and MRI in diagnosis of
different types of glomus tumors.
METHODS
Sixteen patients with glomus tumor were
studied, collected during two-year-duration: Starting
from July 2003 till July 2005. All the patients
were subjected to full history taking, clinical
examination with special emphasis on head and neck
examination. Contrast-enhanced CT and MRI
examination of the temporal bone, skull base and the
upper neck were performed to all patients.
CT Examination of the Temporal Bone:
Helical CT scanners (Siemens Somatom plus 4),
(Picker, PQ-CT) and (Toshiba X vision/GX) were
used and the images were obtained in 1 mm slice
thickness. In a bone window algorithm, a window
level between 300and 400 HU and a window width
between 1200 and 1600 HU were selected. Axial
and coronal scans were obtained covering all the
parts of the temporal bone .Images above the level
of the temporal bone, skull base and upper neck
were performed in a 3-5 mm slice thickness. 40 ml
Iodinated I.V contrast medium were administered to
every studied patient.
MRI Examination:
MRI was performed using 1.5 T MR Scanner
(Philips Gyroscan) and (Toshiba, Visart). The head
coil was used as a receiver coil and the examination
included, axial, coronal and sagittal T1-weighted
spin echo (SE) (TR=500msec, TE=20 msec) and T2weighted turbo spin echo (TSE) (TR=5000msec,
Bull. Alex. Fac. Med. 42 No.2, 2006.
Ettaby et al.
TE=150 msec). The slice thickness 2 mm, interslice
gap 0.2 mm, field of view (FOV) 170 mm2 and
RFOV 90%. The post-contrast series included axial,
coronal and sagittal T1-weighted SE. The following
parameters were utilized when imaging of the
adjacent soft tissues: slice thickness 4 mm, interslice
gap 0.3 mm , FOV 240 mm2 , RFOV 85% ,T1W
sequences (TR=600 msec, TE=15 msec) and T2W
sequences (TR=4000 msec, TE=90 msec) .
Final diagnosis was reached by surgical findings
and histopathological examination
RESULTS
This study was conducted on 16 patients with
glomus tumours. None of them had bilateral
involvement. Ten female and 6 male patients were
encountered. Their ages ranged between 33 to 68
years. The glomus family included 4 patients with
glomus tympanicum, 8 patients with glomus jugulotympanicum and another 4 patients with glomus
jugulare. Four patients of glomus tympanicum
presented on CT by intra-tympanic soft tissue
density mass lesions, filling the tympanic cavity,
leaving the ossicles intact and extending into the
external auditory canal. Two masses were extending
into the aditus-ad-antrum and exerting irregular bone
demineralization of moth-eaten pattern at the tegmen
tympani. On MRI (both T1 and T2 WI), all tumors
showed signal intensity generally more than that of
the surrounding bone marrow and air cells, near to
the signal intensity of the surrounding brain tissues.
All showed intense enhancement after IV contrast
administration. The characteristic salt-and-pepper
pattern could not be detected. (Figure 1)
On CT the glomus jugulo-tympanicum (n=8)
showed irregular demineralization of moth-eaten
pattern (irregular with indistinct margins) involving
the jugular fossa, extending through the jugular plate
and the lateral portion of the carotico-jugular spine.
Further destruction extended anteriorly to the
vertical portion of the carotid canal. The
infralabyrinthine compartment was destroyed, but
superior tumor extension was slowed by the dense
bone of the otic capsule. Spread into hypotympanum
was detected in one intratympanic tumor. Also on
MRI (both T1 and T2 WI), both tumors showed
signal intensity generally more than that of the
surrounding bone marrow and air cells, near to the
signal intensity of the surrounding brain tissues.
They showed intense enhancement after IV contrast
administration. The characteristic salt-and-pepper
pattern could be hardly detected. (Figure 2)
Finally the members of the glomus family, were
four huge tumors of glomus jugulare. The lesions
presented on CT as infralabyrinthine soft-tissue
masses with bony changes similar to those
previously described with glomus jugulotympanicum but more extensive, one of them
destroyed portion of the foramen magnum.
Alexandria Bulletin
Ettaby et al.
Two were extending intraluminally along the
internal jugular vein down to the C3 and C4 level,
appearing as an enhancing mass on CT. Further
posterior extension of one tumor was noted with
growth through the dura to involve the cerebellum.
Again, on MRI (On T1 and T2 WI), all tumors
showed signal intensity generally more than that of
the surrounding bone marrow and air cells, near to
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the signal intensity of the surrounding brain tissues.
Two of them showed intense enhancement after IV
contrast administration and the other two tumors
were very huge showed no appreciable enhancement
(dropout effect). Since all tumors were very large,
the characteristic salt-and-pepper pattern could be
avidly detected. (Figure 3)
A
B
C
D
Figure 1. Glomus Tympanicum
(A,B) Axial and coronal CT scans.(C,D) Coronal T1WI without and with contrast.
Patient of glomus tympanicum presented on CT by intra-tympanic soft tissue density mass lesion, filling the tympanic
cavity, leaving the ossicles intact (A) and extending into the external auditory canal (B). It is extending into the aditus-adantrum and exerting irregular bone demineralization of moth-eaten pattern at the tegmen tympani. On MRI (both T1 pre
& post contrast), The tumor showed signal intensity generally more than that of the surrounding bone marrow and air
cells, near to the signal intensity of the surrounding brain tissues. They showed intense enhancement after IV contrast
administration. The characteristic salt-and-pepper pattern could not be detected.
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SKULL BASE glomus tumour.
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Ettaby et al.
A
B
C
D
E
F
G
Figure 2. Glomus Jugulo-Tympanicum
(A, D) Axial and Coronal CT scans. (B,C,G) axial MRI T1 WI, T1WI with contrast, T2 WI. (E,F) Coronal MRI T1 WI,
T1WI with contrast.
On CT, Patient of the glomus jugulo-tympanicum showed irregular demineralization of moth-eaten pattern (irregular with
indistinct margins) at the jugular fossa extending through the jugular plate and the lateral portion of the caroticojugular
spine. The infralabyrinthine compartment was destroyed. On MRI, (both T1 and T2 WI), the tumors showed signal
intensity generally more than that of the surrounding bone marrow and air cells, near to the signal intensity of the
surrounding brain tissues. It shows intense enhancement after IV contrast administration. The characteristic salt-andpepper pattern could be hardly detected.
Bull. Alex. Fac. Med. 42 No.2, 2006.
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Ettaby et al.
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A
B
C
D
E
F
G
H
Figure 3. Glomus Jugulare
(A - D) Axial CT scans (B-D with contrast).
(E,F) Coronal CT with contrast. (M) Sagittal CT reconstruction with contrast.
(G,H) Axial MRI T1 WI without and with contrast.
A sizable Glomus jugulare presented on CT as infralabyrinthine soft-tissue masses with bony changes similar to that
previously described with glomus jugulo-tympanicum but more extensive. It is seen extending intraluminally down the
internal jugular vein down to the C4 level, appearing as an enhancing mass on CT. Resultant thrombosis of the sigmoid
sinus noted. On MRI (both T1 and T2 WI), the tumor shows signal intensity generally more than that of the surrounding
bone marrow and air cells, near to the signal intensity of the surrounding brain tissues. Since the tumor is very large,
there is no appreciable enhancement (dropout effect). The characteristic salt-and-pepper pattern could be hardly detected.
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SKULL BASE glomus tumour.
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Ettaby et al.
I
J
L
K
M
Continue
Figure 3. Glomus Jugulare
(I, J) Coronal MRI T1 WI without and with contrast.
(K,L) Axial MRI T2 WI
A sizable Glomus jugulare presented on CT as infralabyrinthine soft-tissue masses with bony changes similar to that
previously described with glomus jugulo-tympanicum but more extensive. It is seen extending intraluminally down the
internal jugular vein down to the C4 level, appearing as an enhancing mass on CT. Resultant thrombosis of the sigmoid
sinus noted. On MRI (both T1 and T2 WI), the tumor shows signal intensity generally more than that of the surrounding
bone marrow and air cells, near to the signal intensity of the surrounding brain tissues. Since the tumor is very large,
there is no appreciable enhancement (dropout effect). The characteristic salt-and-pepper pattern could be hardly detected.
Bull. Alex. Fac. Med. 42 No.2, 2006.
Ettaby et al.
Alexandria Bulletin
DISCUSSION
The paraganglioma is the second most common
tumor involving the temporal bone and is the most
common in the middle ear.(1,9) The term glomus
jugulare tumor has been used among clinicians since
Guild(10) named the paraganglia glomus jugulare.
The term glomus tympanicum tumor was introduced
by Alford and Guilford(11) when they noted that
those arising "away from the jugular bulb, in the
middle ear, along the course of Jacobson's nerve"
had a better prognosis than those arising "in the
area of the jugular bulb. Glasscock et al(12) clarified
the definition so that glomus tympanicum tumors
include those in the tympanic cavity and the
mastoid, and glomus jugulare tumors include those
involving the jugular bulb and the base of the skull.
Paragangliomas tend to grow along the planes of
least resistance by following preexisting pathways in
the temporal bone (i.e., fissures, air cell tracts,
vascular channels, and foramina). Tumors
commonly descend through the jugular vein, and
central nervous system invasion may ultimately
cause death. This was stated by Chakeres(13) and
noticed in this study as well.
The identification of either air and or bone
between a tympanic cavity mass and the jugular bulb
characterizes the mass as a tympanicum tumor.
Computed tomography (CT) of the temporal bone is
the best imaging format for this purpose. CT contrast
enhancement and bone algorithm better allow the
identification of small middle ear masses and their
relationship to the dome of the jugular bulb. Bone
and soft tissue windows in the axial and coronal
planes are used. The use of CT in large-lesions
determines the degree of bony destruction as it
relates to the vital anatomy of the temporal bone.
Also, we agree with what was published by Lo
WW et al,(4) reporting the CT bony changes with
paragangliomas as irregular bone erosions with
indistinct margins and may be described as "motheaten. This irregular demineralization is thus often
first found in the jugular plate or in the lateral
portion of the caroticojugular spine. More extensive
destruction extends from around the pars vascularis
and beyond. Further destruction extends medially to
the pars nervosa and the petrooccipital fissure,
anteriorly to the vertical and then the horizontal
carotid canal, and posteriorly along the sigmoid
sulcus to the transverse sulcus. The infralabyrinthine
compartment is frequently destroyed, but superior
tumor extension is often slowed by the dense bone
of the otic capsule. An intratympanic tumor may
spread into the mastoid, and vice versa, the
protympanum, and less often into the epitympanum.
Tumor extent, intracranial tumor extension (ICE),
and vascular involvement are, at present, better
evaluated by MRI. Magnetic resonance imaging
provides unsurpassed data regarding extent of tumor
and tumor relationship to both neural and vascular
Bull. Alex. Fac. Med. 42 No.2, 2006.
335
regional anatomy. Furthermore, MRI offers the best
data differentiating glomus tumors from other
possibilities.
It is used preferentially in identifying
synchronous lesions as well as ICE. The quantitative
(differential diagnostic) capabilities of MRI remain,
as yet, untapped. MRI angiography may well surpass
traditional angiography.
On MRI the characteristic salt-and-pepper pattern
could be detected only in relatively large glomus
jugulare and jugulo-tympanicum. It is not clearly
seen in small cases of glomus tympanicum. The
same was stated by Olsen WL et al(14): In
paragangliomas larger than 2 cm, an apparently
unique salt-and-pepper pattern of hyperintensity and
hypointensity on Tl-weighted and T2-weighted
images has been described.
Only two cases of huge glomus jugulare showed
the dropout effect described by Vogi et al (1993)(15)
in the early enhancement pattern of paraganglioma
due to the fact that if the concentration of
gadolinium is sufficiently high, there is actually a
signal decrease. The signal coming from the tumor
first rises as the bolus reaches the tumor. However,
because of the large volume of blood within the
tumor, the gadolinium transiently reaches a high
enough concentration that there is actually a signal
drop. As the gadolinium concentration of the initial
bolus is diluted, the signal increases once again.
Tumor types other than paraganglioma do not show
this phenomenon may distinguish this lesion from
other tumors.
We concluded that MRI and CT must not be
considered exclusive, and when diagnostically
indicated, each may be employed to supplement the
other. In fact, both MR imaging and CT are usually
required for full assessment of skull base lesions.
The different types of glomus are relatively
consistent in location, configuration, CT density,
MR intensity and enhancement patterns. If one
analyzes each lesion systematically, takes into
consideration the clinical information, and avoids
the traps set by the occasional lesions intruding into
the same anatomical territories, a correct
preoperative diagnosis can be reached in a large
percentage of the cases.
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