Imaging Innovations in

Tem p o r a l B o n e D i s o rd e r s
a b c,
C. Eduardo Corrales, MD , Nancy Fischbein, MD , Robert K. Jackler, MD *

KEYWORDS
 Cholesteatoma  Diffusion-weighted imaging  Paraganglioma
 Whole-body molecular imaging  Dural arteriovenous fistula
 Arteriovenous malformation  Arterial spin labeling

KEY POINTS
 High-resolution computed tomography is a fast and dependable method for assessing
temporal bone anatomy and planning surgical approach in cases of cholesteatoma.
 Diffusion-weighted MRI is likely to decrease the number of second-look surgeries,
decreasing patient morbidity and surgical costs.
 Contrast-enhanced computed tomography of the skull base, MRI of the skull base and
neck, and catheter angiography and embolization in the preoperative period are recom-
mended for evaluation and management of jugular foramen paragangliomas.
 Arterial spin labeling (ASL) is an emerging noninvasive MRI procedure that does not require
gadolinium-based contrast administration and is a useful diagnostic test for dural arterio-
venous fistulas (DAVFs) and small arteriovenous malformations (AVMs) less than 2 cm.
 The absence of venous signal on ASL is a helpful predictor of the presence or absence of
DAVF or AVM in patients with pulsatile tinnitus and no obvious vascular malformation on
routine imaging studies.

INTRODUCTION

Important advances in diagnostic imaging of the temporal bone have been made in the
past decade. The development of new imaging techniques coupled with new treat-
ment algorithms has created new possibilities in treating temporal bone diseases.
This article provides an overview of recent imaging innovations that can be applied
to temporal bone diseases; it does not provide a comprehensive review of temporal

Disclosures: None.
a
Department of Otology, Neurotology and Skull Base Surgery, Division of Otolaryngology-Head
and Neck Surgery, Brigham and Women’s Hospital, Harvard Medical School, 45 Francis Street,
Boston, MA 02115, USA; b Departments of Radiology, Otolaryngology-Head and Neck Surgery,
Neurology, Neurosurgery and Radiation Oncology, Stanford University Medical Center, 300 Pas-
teur Drive, Room S-047, Stanford, CA 94305, USA; c Division of Otolaryngology-Head & Neck
Surgery, Stanford University School of Medicine, 801 Welch Road, Stanford, CA 94305, USA
* Corresponding author.
E-mail address: jackler@stanford.edu

Otolaryngol Clin N Am 48 (2015) 263–280

http://dx.doi.org/10.1016/j.otc.2014.12.002 oto.theclinics.com
0030-6665/15/$ – see front matter Ó 2015 Elsevier Inc. All rights reserved.
264 Corrales et al

Abbreviations

ASL Arterial spin labeling

AVMs Arteriovenous malformations
CBCT Cone beam computed tomography
CT Computed tomography
CTA Computed tomography angiography
DAVFs Dural arteriovenous fistulas
DOPA Dihydroxyphenylalanine
DOTATATE Tetraazacyclododecane tetraacetic acid-octreotate
DSA Digital subtraction angiography
DTPA Diethylenetriaminepentaacetic acid
DWI Diffusion-weighted imaging
EPI Echo-planar imaging
18 18
F-FDG F-fluorodeoxyglucose
HRCT High-resolution computed tomography
IV Intravenous
MIBG Metaiodobenzylguanidine
MR Magnetic resonance
MRA Magnetic resonance angiography
MRV Magnetic resonance venography
NET Neuroendocrine tumors
PGL-1 Paraganglioma syndrome 1

bone disorders and their imaging characteristics, because numerous excellent refer-
ences already exist in textbooks and review articles.1–4
Topics covered in this article include imaging techniques for evaluation of choles-
teatoma and epidermoids, with emphasis on the role of magnetic resonance (MR)
diffusion-weighted imaging (DWI); imaging techniques for evaluation of skull base
neuroendocrine tumors, including paragangliomas, with emphasis on whole-body
molecular imaging; and MR arterial spin labeling (ASL) perfusion for dural arteriove-
nous fistulas (DAVFs) and arteriovenous malformations (AVMs).

Imaging Techniques for Evaluation of Cholesteatoma and Epidermoids

Since its introduction in the early 1980s, high-resolution computed tomography
(HRCT) of the temporal bone has been the gold standard for imaging cholestea-
toma.5–7 HRCT now represents the preeminent modality for defining the bony anat-
omy of the temporal bone, as well as pathologic alterations in that anatomy caused
by cholesteatoma. Although cholesteatoma is usually readily identified based on his-
tory and otoscopic examination, its presence and extent may not always be clear. This
considerable unpredictability in size and extent of cholesteatoma can substantially
affect surgical approach, expectations, and risk, as can the possible involvement of
critical adjacent structures. Despite these strengths of HRCT, in postoperative ears,
residual or recurrent cholesteatoma may be in areas concealed from direct inspection,
leading to the necessity of second-look surgeries for complete evaluation, because
HRCT cannot conclusively distinguish residual or recurrent disease from fluid and
granulation tissue, which have similar density.
Because HRCT is limited in its ability to differentiate among soft tissue densities in
the temporal bone, the addition of MRI, with its superior soft tissue contrast, has been
valuable in the temporal bone. The recent development and refinements of diffusion-
weighted MRI (DW-MRI) have contributed significantly in this regard, allowing accu-
rate identification of the presence of small foci of keratin debris that would otherwise
be impossible to differentiate from fluid, edematous mucosa, and/or granulation tissue
 Innovations in Temporal Bone Imaging 265

on routine MR sequences and HRCT. In this way, the selective use of HRCT and
DW-MRI can provide complementary information that can guide otologic surgeons
in the management of cholesteatoma.
The strength of HRCT is its capacity to image bone. A cholesteatoma appears as a
soft tissue mass, usually occurring in pneumatized regions of the temporal bone. The
normal aeration is lost and the surrounding bone often shows evidence of erosion with
smooth or scalloped margins. Adjacent ossicles may be absent, eroded, or demineral-
ized. The scutum is often eroded, revealing the pathway of ingrowth of epithelium from
the pars flaccida into the epitympanum (Fig. 1). HRCT is also useful in recognizing the
geometry and location of adjacent vital structures. The bony labyrinth, facial nerve ca-
nal, tegmen, sigmoid plate, and carotid canal can all be well seen on HRCT. A careful
study of the HRCT can also reveal anatomic variations that may affect surgery, such as
dehiscence of the facial nerve canal. Similarly, loss of the normal bone overlying any of
these structures may give a valuable warning of involvement by cholesteatoma.
When ossicular or mastoid bony erosion is seen in association with a soft tissue
mass, HRCT can distinguish cholesteatoma with specificity between 80% and
90%.8,9 In the postoperative period, HRCT has a high negative predictive value when
it shows a well-aerated middle ear with no evidence of soft tissue densities.8,10,11 How-
ever, HRCT has proved unreliable in differentiating residual or recurrent cholesteatoma
from granulation tissue, cholesterol granuloma, mucosal edema, fibrosis, scar tissue,
or fluid.10,12,13 However, in patients who have undergone previous tympanomastoidec-
tomy, the relevance of bony erosion is lost because it is difficult or impossible to differ-
entiate surgical changes from pathologic bony destruction caused by cholesteatoma.
In this setting, HRCT has a sensitivity of 43%, specificity of 42% to 51%, and a predic-
tive value of 28% in detecting residual or recurrent cholesteatoma.13,14
The introduction of in-office cone beam computed tomography (CBCT) imaging has
made imaging for cholesteatoma more convenient and accessible.15 As a result of
their favorable radiation safety profile and compact size, CBCT scanners can be
assembled in clinic rooms with often minimal requirements for specialized shielding.

Fig. 1. HRCT of a patient with left cholesteatoma. Axial (A) view shows a sclerotic mastoid
with an erosive cholesteatoma (c) There is tympanosclerosis medial to the ossicular chain.
Coronal (B) view shows typical imaging features, including cholesteatoma (c) showing
scalloped edges, scutum erosion, and a demineralized/eroded ossicular chain. The tegmen
is dehiscent and low lying, making surgical access challenging. The facial nerve canal is
shown to be dehiscent adjacent to the oval window on the coronal image.
266 Corrales et al

In CBCT scanners, the x-ray beam forms a cone-shaped geometry between the imag-
ing source (apex of the cone) and the detector (base of the cone). In contrast, conven-
tional scanners have a fan-beam geometry.16 The radiation dose of these scans is
reported to be 60% of a conventional computed tomography (CT) scanner when eval-
uating middle ear structures,16–18 but middle and inner ear bony structures are seen
equally well in CBCT and conventional HRCT scanners.17 One disadvantage of in-
office CBCT is the limited anatomic coverage, which means inner ear or more distal
disorders in the mastoid may be missed. An additional CBCT disadvantage is the
lack of any soft tissue contrast, and these scanners are typically used only to assess
bony anatomy. A general disadvantage of both HRCT and CBCT is their use of ionizing
radiation, and hence their intrinsic potential for inducing malignancy.19,20 Therefore,
clinicians must always be judicious in their use, particularly in children who may be
sensitive to cumulative radiation effects.

MRI

Although MRI cannot provide a map of the bony geometric framework of the temporal
bone for surgical planning, selected MRI techniques can provide valuable information
regarding the presence, size, and approximate location of cholesteatoma that may
not be available on HRCT imaging. MRI also has the advantage of not requiring expo-
sure to radiation, although it does require longer acquisition times compared with
HRCT, and the need for immobilization may make it difficult to obtain in young
children.
On conventional MRI sequences, cholesteatomas and epidermoids appear dark on
T1-weighted images, bright on T2-weighted images, and do not enhance with intra-
venous contrast unless acute infection results in rim enhancement. These signal char-
acteristics render them difficult to distinguish from much of the other soft tissue
present in a chronic ear condition unless they are large. One mechanism to circum-
vent this limitation has been the use of delayed-contrast techniques. Delayed-
contrast MRI has been used to better detect recurrent cholesteatoma by taking
advantage of the fact that other tissue, such as fibrosis or granulation tissue, often
takes up more contrast given sufficient time,21–24 whereas cholesteatomas do not.
In this technique, T1 images are obtained 30 to 45 minutes after intravenous (IV) para-
magnetic contrast administration (gadolinium), which results in enhancement of
inflammatory mucosa, granulation tissue, scar, or fibrosis. Absence of contrast
enhancement in a lesion suggests cholesteatoma. De Foer and colleagues23 reported
sensitivity and specificity for delayed-contrast MRI in detecting cholesteatoma as
56.7% and 67.6% respectively. Overall positive predictive value was 88% and nega-
tive predictive value was 27% in the population studied. Disadvantages of using
delayed-contrast MRI are (1) the cost and potential morbidity associated with the
need for IV contrast; (2) retained secretions, silicone/plastic (Silastic [Dow Corning,
MI]) sheets, and calcified scars can mimic nonperfused cholesteatoma; (3) early
acquisition of images may lead to false-positives; (4) this technique cannot detect
cholesteatomas smaller than 3 mm; (5) it is difficult for scheduling purposes to
keep an MR scanner available if immediate and delayed scans are both acquired;
and (6) sedation or general anesthesia is required for children because of the
prolonged time required for image acquisition. As a result of these limitations,
delayed-contrast MRI for detecting residual or recurrent cholesteatoma has never
caught on and is not routinely used in most practices.
However, over the last decade the use of diffusion-weighted sequences has pro-
vided considerable improvement in the diagnosis of cholesteatoma and skull base
 Innovations in Temporal Bone Imaging 267

epidermoids, and this sequence is now considered an important component of the

MRI assessment for both diseases. DWI relies on the principles of molecular diffusion
or brownian motion.25 Molecular diffusion refers to the haphazard movement of water
molecules, which is restricted in certain pathologic conditions, including in the pres-
ence of organized keratin debris as seen in both cholesteatoma and epidermoids.26
In regions where the diffusion of water is impeded or restricted, there is less dephasing
of protons and more signal is retained, and hence the tissue with restricted diffusion is
seen as bright on the diffusion-weighted image.10,25 The keratin debris associated
with cholesteatomas and epidermoids restricts water diffusion, and this leads to a
high signal intensity in this material on DWI compared with brain or other surrounding
soft tissues. Granulation tissue, fibrosis, and mucosal edema are less restricting of
water motion and do not lead to high signal on DWI.
Two broad categories of DWI algorithms can be used for initial evaluation of cho-
lesteatoma and epidermoids, or detection of residual or recurrent cholesteatoma:
echo-planar and non–echo-planar DW-MRI. The first algorithm developed was
echo-planar DWI, and many articles have described its use in detecting cholesteato-
mas.12,21–35 Echo-planar imaging (EPI)–based methods are fast and reliable, but they
produce considerable distortion at the skull base and temporal bone related to the
numerous interfaces among air, bone, and soft tissue, and to the inhomogeneity of
the magnetic field that results from these interfaces, as discussed in more detail
later. Non-EPI DW methods are typically either single-shot turbo-spin echo
sequences (half Fourier acquisition single-shot turbo-spin echo [HASTE; Siemens
Systems, Germany]) or multishot turbo-spin echo sequences (periodically rotated
overlapping parallel lines with enhanced reconstruction [PROPELLER]; BLADE
[Siemens Systems, Germany]), and they are less subject to distortion at the skull
base.
As mentioned earlier, EPI DWI is subject to artifacts at the interfaces between tis-
sues, especially when air or bone is adjacent to soft tissue. These magnetic suscep-
tibility artifacts relate to local magnetic field inhomogeneities caused by tissues of
markedly different composition; they can also occur in the vicinity of metallic foreign
bodies, such as surgical clips or staples, or dental work. However, the mastoid and
middle ear produce susceptibility artifacts caused by natural air-bone interfaces,
and this causes image distortion. Multiple studies have shown the inability of EPI
DWI to detect cholesteatomas smaller than 5 mm.10 Studies have also shown newer,
non-EPI DWI methods to be superior to EPI DWI in detecting recurrent or residual
cholesteatoma,26,29,34 and thus non-EPI DWI has become the standard for MRI
imaging of cholesteatoma. Skull base epidermoids located in the cerebello-pontine
angle (CPA) and petroclival junction, have less susceptibility artifacts.
Various studies,26,28,29,34 including a recent meta-analysis,32 have evaluated
DW-MRI for the detection of residual and recurrent cholesteatomas. In the meta-
analysis, the overall sensitivity of this imaging modality was 94% with a specificity
of 94%. Most of the false-negatives reported were caused by cholesteatoma pearls
less than 3 mm in size. False-positives reported in this study were caused by suscep-
tibility artifacts, cholesterol granuloma, abscess, or bone powder; in some of these
cases the image showed a true disorder, but this disorder was not necessarily
cholesteatoma.
Although MRI can be helpful in imaging of cholesteatoma under specific circum-
stances, the cost of MRI is approximately double that of HRCT.36 Although clinicians
should consider this additional economic impact, the benefits gained in selected
patients by avoiding needless surgery, or by preventing a delay in diagnosis, can
potentially justify its use on economic grounds.
268 Corrales et al

INDICATIONS FOR IMAGING IN CHOLESTEATOMA AND EPIDERMOIDS

Experts may disagree about the indications for imaging in cholesteatoma and about
the extent to which it assists in treatment decisions.37 Some otologists routinely obtain
imaging whenever cholesteatoma is seen or suspected, whereas others use imaging
infrequently. Most agree that imaging is indicated in revision cases and those with
intracranial or intratemporal complications. Surgeons should carefully consider the
benefits they receive from imaging in their own practices, and they should regularly
reevaluate imaging indications and referrals as they gain experience and perhaps
modify their surgical techniques accordingly. Surgeons should also be diligent about
reviewing imaging studies themselves, because even the best radiology report rarely
conveys all the subtleties that may affect surgery.
For lesions located in the skull base, such as epidermoids, imaging is routinely
obtained.

Preoperative Assessment
The benefits of being aware of potential challenges and of having a CT-based guide for
surgical planning are particularly helpful in teaching settings, so that expectations for
the case can be reviewed preoperatively. Similarly, HRCT can be helpful before
revision surgery, especially when the surgeon did not perform the initial procedure.
In revision cases, anatomy may be considerably altered, limiting the utility of normal
surgical landmarks and presenting unexpected challenges.
HRCT can reveal specific patterns of pneumatization and aeration or variability in the
position of the sigmoid sinus or tegmen, which may affect surgical access to the dis-
order. Is a mastoidectomy needed, or can the disease be adequately accessed via a
transcanal approach? Is there likely to be adequate space to access disease with the
canal wall left up, or is the mastoid sclerotic and contracted, warranting a canal-wall-
down procedure? Erosion of the Fallopian canal may be suggested, as can exposure
of the carotid artery or jugular bulb, and these findings are important alerts to potential
hazards during dissection. Some labyrinthine fistulae are clinically silent,38 as are almost
all facial nerve canal erosions, thus preoperative knowledge of these findings may alert
the surgeon to areas that warrant extra intraoperative care and attention. Although the
ossicles are difficult to assess completely, obvious ossicular abnormalities may predict
the need for ossicular reconstruction. HRCT can also show unexpected and potentially
unrelated anatomic variations such as anomalous facial nerve patterns.39
Despite MRI’s superior ability to identify cholesteatoma and differentiate it from
other soft tissues, it is seldom helpful in the preoperative setting in primary cases
unless there is a question about the preoperative diagnosis of cholesteatoma; in these
cases, DW-MRI can provide additional information when clinical information is limited
or the otoscopic examination is inconclusive. However, most of the time the diagnosis
is not in doubt and HRCT is superior in providing information on relevant anatomic
geometry. DW-MRI becomes considerably more useful in assessing the potential
for postoperative recurrence of disease. In such cases, cholesteatoma may appear
in areas inaccessible to clinical otomicroscopy or in unexpected areas, including
the mastoid cavity, deep to reconstructive materials, and growing around adjacent
structures where the furthest extent of cholesteatoma may have been missed on
the primary procedure (Fig. 2). DW-MRI images must be interpreted in conjunction
with other MRI sequences, because not all high-signal-intensity tissue on DW-MRI
is cholesteatoma. In these cases, the use of other MRI sequences may be useful to
predict an alternative diagnosis such as cholesterol granuloma, and to provide the
surgeon and patient with expectations for treatment.
 Innovations in Temporal Bone Imaging 269

Fig. 2. Recurrent cholesteatoma (arrow) eroding the retrofacial air cells 25 years following a
prior canal-wall-up tympanomastoidectomy. The patient’s tympanic cavity showed no evi-
dence of disease on otoscopy. (A) HRCT shows a nonspecific erosive soft tissue lesion with
loss of bone over the sigmoid sinus and posterior fossa dura. (B) DWI-MRI shows focal
high signal associated with the lesion, consistent with recurrent cholesteatoma (arrow).

Similarly, for epidermoids of the skull base, DWI-MRI is an extremely useful

sequence to differentiate from arachnoid cysts (Fig. 3).

Postoperative Surveillance
It is compelling to look for alternatives to second-look surgery. If HRCT shows no
abnormal soft tissue at 6 or 9 months following the initial stage, clinicians may be
comfortable holding off on a second look.8,10,11,37 However, it is rare that an HRCT
study shows no nonspecific, potentially suspicious soft tissue. Also, in an early post-
operative ear, bone erosion cannot be used to help differentiate the soft tissue from
scar, fluid, or edema, and this is likely the situation in which DW-MRI is most useful
in assessing cholesteatoma.
If postoperative imaging is done too early, false-negative DW-MRI may result. How-
ever, after 9 to 12 months, most persistent cholesteatomas are larger than 3 mm and

Fig. 3. Large epidermoid of the right cerebellopontine angle. (A) Axial T1-weighted image
shows the lesion (arrow) to be of low signal intensity. (B) Axial postgadolinium T1-weighted
image shows no enhancement of this lesion (arrow). From these sequences, it is nearly
impossible to differentiate between an arachnoid cyst and an epidermoid. (C) Axial
diffusion-weighted image shows a markedly increased signal intensity of the lesion (arrow),
consistent with reduced diffusion, and thus an epidermoid.
270 Corrales et al

therefore should be apparent on correctly performed DW-MRI.26,28,29,32,34 A negative

DW-MRI study may avoid the expense and morbidity associated with a negative
second look. The surgeon needs to make the judgment regarding repeat surgery or
imaging follow-up based on the likely area of involvement as to whether a recurrence
of 3 mm or greater is unacceptably large. In some areas, such at the mastoid cavity, a
recurrent lesion of this size can usually be readily resected. In other areas, such as the
sinus tympani or on the stapes footplate, a cholesteatoma of 3 mm may present a
greater surgical challenge. If this is the case, then foregoing imaging and proceeding
directly to a second-look procedure is reasonable. If a DW-MRI study is negative at 9
to 12 months postoperatively, the surgeon should use clinical judgment as to whether
another scan is needed at a later date. In routine cases, a single postoperative scan at
9 to 12 months may be sufficient, and the patient can be followed clinically. However, if
there is concern for persistence in areas that are inherently more difficult to assess,
such as the jugular foramen or petrous apex, then another scan obtained a year later
is a reasonable option.

Cholesteatoma Complications
In patients with complications of cholesteatoma, imaging is almost always indi-
cated.21,34,40,41 MRI is well suited for defining intracranial complications such as brain
abscess or epidural abscess, or sinus thrombosis, although contrast-enhanced CT
can also be informative and is indicated if there are contraindications to MRI. MR
venography (MRV) or CT venography may be helpful to evaluate for septic sigmoid
thrombosis. In the setting of complications, clinicians may wish to obtain both
HRCT and MRI studies, because each may offer valuable insights into diagnostic
and therapeutic implications.

WHOLE-BODY MOLECULAR IMAGING IN PARAGANGLIOMAS OF THE JUGULAR

FORAMEN

The most common paraganglioma in the head and neck region is the carotid body
tumor, followed by paraganglioma of the jugular bulb (jugulare), middle ear (tympani-
cum), and vagal paragangliomas.42 Tympanic paragangliomas are the most common
primary neoplasms of the middle ear43 and jugular paragangliomas are the most com-
mon tumors of the jugular foramen.44 The most common symptoms for both jugular
and tympanic paragangliomas are pulsatile tinnitus and hearing loss.43,45–48 CT and
MRI allow accurate preoperative assessment of tumor involvement of the temporal
bone and skull base, as well as an evaluation for intracranial extension.

High-resolution Computed Tomography

Thin-section HRCT scan (<1 mm) in both axial and direct planes or, more commonly,
reconstructed coronal plane is the imaging modality of choice to assess for temporal
bone involvement and to visualize bony structures and tumor extension (Fig. 4). HRCT
scan is useful to discriminate between paragangliomas that arise from the middle ear
(tympanic) and paragangliomas arising from the jugular bulb (jugular). Although tem-
poral bone HRCT is typically done without contrast, suspicion of a vascular mass is
an indication for a contrast-enhanced temporal bone CT, because paragangliomas
enhance intensely postcontrast. The characteristic location, pattern of bone erosion,
and intense enhancement generally allow paragangliomas to be differentiated from
most benign and malignant tumors of the skull base. In patients with pulsatile tinnitus
and a vascular middle ear mass, HRCT helps to easily differentiate among paragan-
glioma, aberrant internal carotid artery, and a dehiscent jugular bulb,49,50 and imaging
 Innovations in Temporal Bone Imaging 271

Fig. 4. CT and MRI of a jugular paraganglioma. Jugular paragangliomas often extend to

involve the hypotympanum, and show an irregular or moth-eaten appearance at the
jugulo-carotid spine, jugular foramen, and/or hypoglossal canal, as seen in (A, arrows). In
this particular case, the paraganglioma had extended out to the external auditory canal.
On gadolinium-enhanced MRI, there is intense enhancement caused by the enormous vascu-
larity of these tumors (B, axial; C, coronal; arrows). In tumors more than 2 cm, the character-
istic salt-and-pepper appearance of paragangliomas corresponds to macroscopic flow voids.

is indicated before biopsy of a vascular mass in the middle ear. In addition, because
paragangliomas may be multiple, contrast-enhanced CT can identify synchronous
tumors of the temporal bone and upper neck.
Tympanic paragangliomas appear as well-circumscribed soft tissue masses in the
middle ear, typically overlying the cochlear promontory, without gross bone erosion.
Jugular paragangliomas are centered on the jugular foramen, involve the hypotym-
panum, and show an irregular or moth-eaten appearance of bone around their
margins.51–53 Careful attention must be given to the relationship between the tumor
and the bony covering of the jugular bulb (the jugular plate). Erosion of the jugular plate
suggests a jugular paraganglioma.

MRI
On MRI, paragangliomas are generally intermediate in signal on T1-weighted and
T2-weighted images, enhance intensely after gadolinium administration, and larger le-
sions (>2 cm) show intratumoral and peritumoral flow voids that are characteristic of
these tumors (the salt-and-pepper appearance) (see Fig. 4). MRI provides superior
soft tissue details compared with HRCT because of its intrinsic soft tissue contrast
resolution; additionally, because it lacks the bone artifact that is seen on CT scans,54
it is particularly helpful to identify tumor extension intracranially. MR angiography
(MRA), MRV, and catheter angiography provide information on the involvement of
the great vessels and allow preoperative embolization. Compression of the internal
carotid artery can be evaluated with MRA, whereas MRV can assess for occlusion
of the jugular bulb and sigmoid sinus by tumor and allows assessment of collateral
venous drainage.

Angiography and Embolization

Angiography serves multiple purposes. First, it provides complementary diagnostic in-
formation by showing the characteristic highly vascular nature of these lesions. How-
ever, formal intravascular angiography is not performed only for diagnostic purposes,
but is combined with embolization in the preoperative period. Second, it allows iden-
tification of dominant feeding vessels that can then be embolized to reduce blood loss
during surgical removal. Third, it identifies collateral vessels associated with the
272 Corrales et al

carotid and vertebral arteries that must be spared during surgery. Fourth, contralateral
venous system patency can be fully assessed. Fifth, the presence of major venous
sinus occlusion by tumor can be confirmed, and, sixth, it may help to identify multi-
focal tumors. Studies have shown decreased operative time and intraoperative blood
loss with preoperative embolization of jugular paragangliomas,55,56 and preoperative
embolization facilitates complete resection of jugular paragangliomas. Angiography
with embolization for jugular paragangliomas is usually performed 1 or 2 days before
surgical excision because a longer interval between embolization and surgery may
result in revascularization of the tumor, which may paradoxically increase intraopera-
tive blood loss.55 Because of their small size and easy accessibility, embolization of
tympanic paragangliomas is not usually performed.

Nuclear Medicine Imaging

Multiple nuclear medicine–based methods have been applied for detection of head
and neck paragangliomas. Octreotide is a somatostatin analogue that, when coupled
to an appropriate tracer, produces a scintigraphic image of neuroendocrine tumors
that express somatostatin type 2 receptors.57 Octreotide scintigraphy imaging (the
most common radioligand is 111In-diethylenetriaminepentaacetic acid [DTPA]–octreo-
tide) has been applied for the diagnosis of head and neck neuroendocrine tumors
(NET) including paragangliomas, Merkel cell carcinomas, medullary thyroid carci-
nomas, and esthesioneuroblastomas, as well as recurrent paragangliomas
(Fig. 5).58,59 However, 111In-DTPA-octreotide scintigraphy has limited spatial resolu-
tion and does not reliably diagnose lesions less than 1 cm.60 Whole-body 123I and
131
I metaiodobenzylguanidine (MIBG) scintigraphy are additional nuclear medicine

Fig. 5. Neuroendocrine tumor of the foramen magnum in an 81-year-old man with meta-
static disease. (A) Low-resolution 111In-DTPA-octreotide scintigraphy showing metastatic le-
sions in the liver (black arrows). (B) In the same patient as in A, 68Ga-tetraazacyclododecane
tetraacetic acid-octreotate (DOTATATE) PET/CT shows improved detail of liver metastatic dis-
ease (black arrows), as well as an additional metastatic lesion at the foramen magnum that
was not previously seen on octreotide scintigraphy (arrowhead); there is physiologic uptake
in the pituitary and salivary glands, spleen, and kidneys. (C) The foramen magnum meta-
stasis is clearly defined on an axial PET/CT fusion (white arrow); there is physiologic uptake
in the parotid glands.
 Innovations in Temporal Bone Imaging 273

studies that have been applied to the diagnosis of paraganglioma but also have dis-
advantages, including 2 patient visits because the images are captured 2 and 24 hours
after tracer injection, and that the tracer accumulates in salivary glands, which may
interfere with clear visualization and diagnosis.61 MIBG whole-body scintigraphy is
able to detect primary paragangliomas of the head and neck,62 but its accuracy in
detecting small paragangliomas at early stages during screening programs, especially
when located in the head and neck region, is limited.63,64 So, despite early reports of
the excellent diagnostic performance of whole-body MIBG scintigraphy in the evalu-
ation of patients with head and neck paragangliomas, this modality has not achieved a
significant place in practice.65 However, a newer generation of radiotracers has been
developed, and these more specific molecular markers allow targeted molecular
imaging. In addition, the use of positron-emitting radiotracers allows higher resolution
images to be created that can easily be fused with CT to create high-quality maps.

NOVEL RADIOTRACERS FOR PARAGANGLIOMA IMAGING

Several novel radiotracers have been developed and tested with the goal of achieving a
more comprehensive molecular fingerprint of paragangliomas of the head and
neck.59,61,66,67 In addition, a focus on positron-emitting tracers allows high-resolution
clinical imaging with PET CT. Studies using 68Ga-tetraazacyclododecane tetraacetic
acid-Tyr-octreotide PET in NETs have shown promising results, with a higher rate of
lesion identification than is achieved with conventional 111In-DTPA-octreotide scinti-
graphy.68–70 Another tracer, tetraazacyclododecane tetraacetic acid-octreotate
(DOTATATE), is an somatostatin receptor-2 (SSTR-2) analogue that, coupled with the
positron emitter 68Ga, has been used for detecting NET, including paragangliomas.60,71
In one study in patients with negative or equivocal 111In-DTPA-octreotide findings,
68
Ga-DOTATATE PET identified additional lesions and altered management in most
cases (see Fig. 5).60 Another such tracer, 18F-fluorodihydroxyphenylalanine
(18F-DOPA), is used for PET and has shown excellent results in early studies for diag-
nosing head and neck paragangliomas.61 18F-DOPA is a radiolabeled dopamine pre-
cursor that is decarboxylated to dopamine inside catecholamine-secreting cells and
subsequently stored in the intracellular vesicles. In one study, 18F-DOPA PET showed
increased accuracy in detecting paragangliomas compared with MIBG.72 The addition
of PET/CT fusions has increased specificity and sensitivity in the diagnosis of head and
neck paragangliomas. One study showed that 18F-DOPA PET/CT in combination was
more accurate in diagnosing and localizing adrenal and extra-adrenal masses suspi-
cious for pheochromocytomas than was 18F-DOPA PET or CT alone.73 A recent
meta-analysis specifically using whole-body imaging using either 18F-DOPA PET or
18
F-DOPA PET/CT for diagnosing paragangliomas showed 91% sensitivity and 95%
specificity, although these percentages increased when patients with succinyldehy-
drogenase (SDHB) mutation were excluded, highlighting the importance of obtaining
genetic testing.74 Multiple studies have confirmed that 18F-DOPA PET/CT performs
better in detecting paragangliomas arising as part of a specific SDH syndrome. For
example, the paraganglioma syndrome 1 (PGL-1–SDHD mutation) typically manifests
as well-differentiated paragangliomas that mainly express a dopaminergic pathway
and thus are 18F-DOPA avid. More aggressive paragangliomas like PGL-4 (SDHB mu-
tation) have reduced dopaminergic activity but have an augmented glycolytic meta-
bolism and thus tend to have better 18F-fluorodeoxyglucose (18F-FDG) avidity
compared with paragangliomas in the PGL-1 syndrome. Consequently, paraganglio-
mas in patients with PGL-1 syndrome show high 18F-DOPA metabolism and low 18F-
FDG avidity, whereas paragangliomas in PGL-4 syndrome tend to have high avidity
274 Corrales et al

for 18F-FDG and low 18F-DOPA activity.75–77 Although CT and MR can define the pres-
ence and anatomic relationships of these lesions, molecular imaging provides an addi-
tional level of differentiation among similar-appearing tumors, and should eventually
support the development of targeted therapeutics.

ARTERIAL SPIN LABELING FOR DIAGNOSING DURAL ARTERIOVENOUS FISTULAS AND

ARTERIOVENOUS MALFORMATIONS

Pulsatile tinnitus is a common clinical symptom that arises from either increased blood
flow or stenosis of a vascular lumen and is classified as arterial or, more commonly, as
venous according to the vessel of origin.78 The initial evaluation of a patient complain-
ing of pulsatile tinnitus begins with a careful history and otoscopic examination.
Should a middle ear mass be seen on examination, then a dedicated temporal bone
CT scan should be obtained to better characterize the lesion and analyze its extent.
A more difficult situation arises if the clinician does not identify any middle ear disor-
der. The differential diagnosis is broad, ranging from benign vascular lesions such as
venous stenosis and diverticula to potentially more serious causes including DAVFs
and AVMs. DAVFs and AVMs are cerebral vascular malformations characterized by
arteriovenous shunting, with direct communication between the arterial and venous
circulations without an intervening capillary bed. AVMs are congenital vascular malfor-
mations that most commonly affect the brain parenchyma and typically present with
acute hemorrhage, seizures, or other neurologic deficits, and they uncommonly pre-
sent as pulsatile tinnitus only. DAVFs are usually acquired and many causes have
been proposed, including infections, trauma, surgery, venous thrombosis, neoplasms,
or hypercoagulable states. DAVFs of the skull base commonly have pulsatile tinnitus
alone as a presenting symptom, and the inclusion or exclusion of DAVF is often an
important component of the work-up of pulsatile tinnitus.
The most common site of intracranial DAVFs is the junction of the transverse and
sigmoid sinuses, and these patients often present with unilateral pulsatile tinnitus.79
However, patients may present with more vague symptoms, such as headache. If
left untreated, these lesions may have serious consequences caused by intracranial
hypertension, chronic venous ischemia, and/or intracerebral hemorrhage, and hence
it is crucial to diagnose these lesions and to refer them for appropriate treatment.
Digital subtraction angiography (DSA) has long been considered the gold standard
for diagnosis, because its time resolution and spatial resolution allow the diagnosis of
even very small DAVFs. Nevertheless, DSA is an invasive procedure that includes
exposure to radiation, requires iodinated contrast injection, and carries a nonnegli-
gible morbidity that generally relates to the risk of groin hematoma or stroke. Thus,
there has been considerable interest in improving the noninvasive diagnosis of
DAVF using other modalities, such as MRI/MRA/MRV (Fig. 6) and CT/CT angiography
(CTA).78,80,81 Narvid and colleagues80 demonstrated the use of CTA for DAVFs. The
observed CTA findings included enlarged feeding arteries, shaggy venous sinuses
caused by enlarged feeder vessels, and asymmetric contrast opacification of the
jugular veins; in this small study, sensitivity and specificity for DAVF exceeded 90%.
MRA, either standard or time resolved, provides an additional noninvasive option for
diagnosing DAVFs, but its sensitivity and specificity for small lesions are also limited.
Although large DAVFs and AVMs are typically easily detected on CT/CTA or MRA/
MRV, because enlarged abnormal feeding and draining vessels can be directly iden-
tified, smaller DAVFs and AVMs may present with only nonspecific imaging signs,
such as secondary evidence of intracranial hypertension, and subtly enlarged vessels
may be overlooked.82
 275

Fig. 6. A 41-year-old woman with left pulsatile tinnitus. (A, B) Before and after gadolinium-
enhanced T1-weighted MRI (with fat saturation on B) showing subtle increase in vascularity
with asymmetrical flow voids in the left hypoglossal canal. (C) MRA with asymmetrical vascularity
on the left side, and subtle tangle of vessels (arrow). (D) MRV with abnormal or asymmetrical
flow related enhancement in left transverse and sigmoid sinuses, signifying possible thrombosis,
stenosis, or flow reversal (arrows). (E) ASL image is very low resolution, but shows intense
signal down at the left skull base (arrow), localizing to sigmoid sinus and jugular bulb compared
with other anatomic images. This finding is diagnostic of a hypervascular tumor or a shunting
lesion. Because the other images show no evidence of a mass, this is consistent with an arterio-
venous shunt, and the noninvasive MRI suggests a left DAVF. (F) Angiography, lateral view, left
external carotid artery injection. Fistulous communication between multiple arterial feeders
and a narrow, irregular distal transverse sinus at the transverse-sigmoid junction (arrow).
276 Corrales et al

ASL is an emerging noncontrast, noninvasive MR technique in which arterial blood

is magnetically labeled just below the region (slice) of interest by applying a 180 radio-
frequency inversion pulse; using this method, the patient’s own blood serves as a
diffusible flow tracer downstream.80,83 When imaging the brain under normal condi-
tions, the labeled blood perfuses the capillary bed, and during this time it undergoes
T1 decay and loses its signal.84 However, blood that circumvents the capillary bed and
is shunted directly from arteries into veins can be detected in the draining venous
structures of an arteriovenous shunt lesion, because it maintains its label and hence
its signal.85 Because DAVFs and AVMs lack a capillary bed there is no water extraction
and the transit time is shortened, resulting in venous ASL signal intensity (see Fig. 6).
Le and colleagues85 recently showed that ASL is a useful diagnostic test for DAVFs
and small (<2 cm) AVMs. Although additional studies are needed, the presence or
absence of venous signal on ASL should be a helpful predictor of the presence or
absence of DAVF or AVM in patients with pulsatile tinnitus and no obvious vascular
malformation on routine imaging studies.

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