AJR 2005; 184:579-587
© American Roentgen Ray Society
Role of 18FFDG PET/CT in the Treatment of Head and Neck Cancers: Principles, Technique, Normal Distribution, and Initial Staging
Vibhu Kapoor1,2,
Melanie B. Fukui3 and
Barry M. McCook1
1 Department of Radiology, Division of PET/CT Imaging, University of Pittsburgh
Medical Center, Pittsburgh, PA 15213.
2 Present address: 301 Frank Cushing Way, Suite 501, Tuman, GU 96913.
3 Department of Radiology, Allegheny General Hospital, Pittsburgh, PA
15213.
Received April 15, 2004;
accepted after revision July 26, 2004.
Address correspondence to V. Kapoor
(ajr{at}kapoorv.us).
Introduction
Head and neck cancers constitute approximately 2–3% of all cancers in
the United States [1], with
approximately 50,000 new cases diagnosed every year. Treatment of head and
neck tumors is challenging. A multidisciplinary approach that includes medical
oncology, radiation therapy, surgery, and radiology results in optimal patient
care. Although the superficial extent of most primary carcinomas on the head
and neck is evident by clinical examination, depth of tumor invasion, lymph
node status, and other synchronous and metachronous primary lesions are best
evaluated on imaging. Currently the most widely accepted cross-sectional
imaging technique is CT (and in some institutions MRI) for the initial
evaluation and follow-up of these patients. An additional imaging technique in
the evaluation of patients with head and neck cancers is 18FFDG
PET.
Molecular imaging using radiopharmaceuticals that are incorporated into
metabolic pathways of normal and abnormal cells for diagnosis and treatment of
cancers is an area of ongoing research. Various radiopharmaceuticals are being
currently investigated for clinical use such as 18FFDG,
11Cmethionine, 11Ctyrosine, 11Cthymidine, and
18Ffluroide [2]. The
most extensively studied and clinically utilized diagnostic
radiopharmaceutical is 18FFDG. PET using 18FFDG has been
approved by Medicare for diagnosis, staging, and follow-up (restaging) of
numerous malignancies such as lymphoma, melanoma, and head and neck, non-small
cell lung, colorectal, breast, thyroid, and esophageal cancers. Cancer
detection on CT and MRI is dependent on changes in morphology (size, shape),
electron density (attenuation on CT), or proton environment and density
(signal intensity on MRI) in abnormal tissue. With 18FFDG PET,
cancer detection is based on changes in glucose metabolism in tumor cells
[3]. It is intuitive that
abnormal metabolic changes at a cellular level should be detectable before
macroscopic morphologic changes and that PET may be more accurate than CT or
MRI for staging tumors and evaluation for recurrent tumors that have undergone
treatment changes. Although no large studies comparing PET/CT to CT or MRI
alone in staging head and neck cancer have been published, some reports have
suggested that PET/CT may be a better examination for the staging of patients
with lung and colorectal cancers
[4,
5].
PET is limited by poor spatial resolution that may make it difficult to
accurately localize 18FFDG uptake to an anatomic structure. This
limitation has been significantly reduced by combined PET–CT, a
technique in which both PET and CT are performed sequentially during a single
visit on a hybrid PET/CT scanner
[6]. The PET and CT images thus
obtained are coregistered using fusion software, thereby enabling accurate
designation of physiologic data obtained on PET to anatomic structures
visualized on CT. We have found that using PET/CT increases our level of
confidence in staging and evaluating tumor recurrence in patients with head
and neck cancers. At our institution, patients with neck carcinoma are
routinely evaluated on PET/CT for initial staging and followup after
treatment. One must, however, be aware of certain pitfalls of this technique
that may lead to both false-positive and false-negative results.
This pictorial essay addresses the principles of 18FFDG PET/CT,
normal FDG uptake in the neck tissues, and the role of 18FFDG
PET/CT in the diagnosis and initial staging of head and neck tumors.
Principle of 18FFDG PET/CT
The technique of 18FFDG PET is based on the detection of
coincident annihilation photons released during decay of 18FDG
[4]
(Fig. 1). Neovascularization is
essential to the proliferation of malignant cells; however, even in the
presence of oxygen, these cells have a high rate of glycolysis. The glycolysis
phenomenon was first described by Otto Warburg in 1924 and is known as the
Warburg effect [7].
Metabolically active cells use a facilitated transport system for glucose
uptake. 18FFDG is a glucose analogue that competes with glucose for
the same transport system. Unlike glucose, however, after initial
phosphorylation into FDG-6-phosphate, FDG cannot undergo further metabolism
and thus it accumulates in metabolically active tumor cells
[8]
(Fig. 2). Because glucose
competes with 18FFDG for uptake into metabolically active cells, it
is important to have adequate blood glucose control to improve the sensitivity
of the examination.
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Fig. 1. —Diagram illustrates principle of PET with 18FFDG:
annihilation reaction. Positrons (ß+) released spontaneously from
decaying fluorine-18 component of 18FFDG nucleus annihilate with
electrons (ß-), releasing two coincident 511-keV photons ( ) that
are detected by scintillation crystals (blue rectangles). P = protons (red), N
= neutrons (blue). Source: Kapoor V, McCook BM, Torok FS. An introduction to
PET-CT imaging. RadioGraphics 2004;24:523–543. Reprinted with
permission.
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Fig. 2. —Diagram illustrates mechanism of action of 18FFDG,
in which glucose analog18FFDG is taken up in facilitated transport
by metabolically active cells via glucose transporters (Glut) in cell
membrane. In cell cytoplasm, 18FFDG undergoes phosphorylation to
form FDG-6-phosphate (FDG-6-P) that, unlike glucose, cannot undergo further
metabolism and becomes trapped in cell with only negligible amount of FDG-6P
diffusing from cells. Source: Kapoor V, McCook BM, Torok FS. An introduction
to PET-CT imaging. RadioGraphics 2004;24:523–543. Reprinted
with permission.
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The standardized uptake value (SUV) is a semiquantitative method for
assessing 18FFDG uptake in tissues and is determined using the
following formula:
At our institution, we consider an SUV of greater than 3.0 (Fig.
3A,
3B) suggestive of malignancy in
the appropriate clinical setting. SUV has also been used to follow up response
to therapy. Because SUV is dependent on a patient's body weight and the
radiotracer injected, corrections for residual activity in the syringe and
tubing and for the dose of 18FFDG at time of injection are required
to prevent incorrect results
[1]. However minor errors in
SUV determination are unlikely to affect patient treatment significantly.
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Fig. 3A. —Standardized uptake value (SUV) is semiquantitative method to
determine 18FFDG uptake by tissues and may help in distinguishing
malignant from benign processes as illustrated by these fused
18FFDG PET/CT images. In 45-year-old man with left tonsil lymphoma,
coronal fused 18FFDG PET/CT image obtained at level of oropharynx
shows marked asymmetry of 18FFDG uptake in tonsils with
hypermetabolism in left tonsil (arrowhead) extending into soft
palate. Visualization of asymmetric uptake and maximal SUV of 9.07 in left
tonsil helped direct biopsy that revealed mantle cell lymphoma.
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Fig. 3B. —Standardized uptake value (SUV) is semiquantitative method to
determine 18FFDG uptake by tissues and may help in distinguishing
malignant from benign processes as illustrated by these fused
18FFDG PET/CT images. In 50-year-old man with benign parapharyngeal
cyst, axial fused 18FFDG PET/CT image obtained at level of mandible
shows cystic mass (straight arrow) in left parapharyngeal
(prestyloid) space with negligible 18FFDG uptake, suggestive of
benign lesion. On resection, mass proved to be infected congenital second
branchial cleft cyst. Arrowhead marks increased uptake by infected molar, and
curved arrow marks physiologic uptake by pharyngeal mucosa.
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In certain situations, it may be difficult to accurately locate an area of
increased activity on PET alone due to the absence of identifiable anatomic
structures, particularly in the abdomen and sometimes in the neck (Fig.
4A,
4B,
4C). Investigators recognized
this limitation in oncology imaging, and Beyer et al.
[6] at the University of
Pittsburgh designed and built the first prototype PET/CT scanner to be used in
clinical imaging. The software used by the combined scanner precisely
coregisters the PET and CT images obtained during a single study on the hybrid
PET/CT scanner (Fig. 5). The
overall combination allows focal FDG uptake on PET to be located with greater
confidence because the relative PET and CT "weighting" of the
coregistered images can be altered, thus enabling FDG uptake to be precisely
mapped to an anatomic structure (Fig.
5). However, the precision of coregistration is only as good as
the patient's ability to remain immobile between the CT and PET portions of
the examination. Movement between the two examinations may result in
misregistration artifact. Motion due to involuntary activity is not as much a
problem in 18FFDG PET/CT of the head and neck as in examinations of
the chest or abdomen. Adequate patient instruction and immobilization during
scanning can prevent misregistration due to voluntary movements.
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Fig. 4A. —42-year-old woman with non-Hodgkin's lymphoma evaluated for
restaging showing coregistration advantage of fused 18FFDG PET/CT
over 18FFDG PET. Axial 18FFDG PET image of neck shows
focal areas of hypermetabolism in posterior neck bilaterally
(arrowheads), with maximal uptake of 4.19 standardized uptake value
that suggests malignant lymphadenopathy. Arrows mark increased uptake
anteriorly in midline that is due to physiologic tongue muscle or hard palate
mucosa uptake.
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Fig. 4B. —42-year-old woman with non-Hodgkin's lymphoma evaluated for
restaging showing coregistration advantage of fused 18FFDG PET/CT
over 18FFDG PET. Corresponding axial fused 18FFDG PET/CT
(B) and CT (C) images show posteriorly located hypermetabolic
areas to be in brown fat around muscles (arrowheads) and anteriorly
located hypermetabolic areas to be in hard palate mucosa (arrows).
Hence, CT helps in accurate localization of 18FFDG uptake. Box in
center of C gives attenuation data.
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Fig. 4C. —42-year-old woman with non-Hodgkin's lymphoma evaluated for
restaging showing coregistration advantage of fused 18FFDG PET/CT
over 18FFDG PET. Corresponding axial fused 18FFDG PET/CT
(B) and CT (C) images show posteriorly located hypermetabolic
areas to be in brown fat around muscles (arrowheads) and anteriorly
located hypermetabolic areas to be in hard palate mucosa (arrows).
Hence, CT helps in accurate localization of 18FFDG uptake. Box in
center of C gives attenuation data.
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Fig. 5. —57-year-old man with squamous cell tongue cancer. Sagittal
images of neck show differential PET/CT weighting possible with fused
18FFDG PET/CT. Images may be viewed as only CT scans (left image),
only PET scans (right image), or varying combination of both (middle image) by
dragging vertical bar at the bottom of the image (arrow). Physiologic
and anatomic fusion is possible as scanning is performed without moving
patients from gantry table between CT and PET portions of examination.
Voluntary or involuntary patient motion may result in misregistration
artifact. Arrowheads mark abnormal 18FFDG uptake at base of
tongue.
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All 18FFDG PET/CT scans are obtained on a dedicated hybrid
PET/CT system (CTI PET, Siemens Medical Solutions) and viewed after
attenuation correction on a fusion workstation using the Syngo software
platform (Siemens Medical Solutions). Before scanning is performed, the
patient is injected IV with 370 MBq (10 mCi) 18FFDG and then is
instructed to lie quietly in a room to decrease muscle and vocal cord uptake.
Approximately 60 min after the injection, a contrast-enhanced CT scan from the
skull base to iliac crests is obtained on a single-detector helical scanner
(which is a component of the hybrid PET/CT scanner) with a collimator width of
5.0 mm and a pitch of 1.5. A PET scan is obtained immediately after the CT
scan without allowing the patient to move on the gantry table between the two
acquisitions so that the images can be accurately coregistered.
Normal Distribution of 18FFDG in the Head and Neck
Numerous structures in the neck show physiologic uptake of FDG. These
include muscles (tongue and paraspinal muscles, vocal cords), lymphoid tissue
(mucosa-associated lymphoid tissue, palatine and lingual tonsils), brown fat,
and salivary glands [9,
10] (Fig.
6A,
6B,
6C,
6D,
6E,
6F,
6G,
6H,
6I,
6J). A high SUV (in the
malignant range) may be seen in these normal tissues as a result of
physiologically increased metabolic activity (Fig.
6A,
6B,
6C,
6D,
6E,
6F,
6G,
6H,
6I,
6J), and sometimes it may not
be possible to distinguish benign from malignant disease on the basis of SUV
alone. In such cases, the pattern of FDG uptake in the neck may be more
helpful. For example, in a patient with metastasis of unknown primary cancer,
asymmetry in uptake in the tonsils or tongue base may help guide biopsy (Fig.
3A,
3B). Occasionally,
differentiation between normal and abnormal 18FFDG uptake may be
difficult on PET alone; PET/CT may be valuable in such situations by
accurately localizing increased 18FFDG uptake (Fig.
4A,
4B,
4C).
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Fig. 6A. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Sagittal fused
18FFDG PET/CT image of 40-year-old man shows 18FFDG
uptake (arrows) in normal brain.
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Fig. 6B. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Axial 18FFDG
PET/CT images show normal 18FFDG uptake in lymphoid tissues of
nasopharynx (straight arrows, B), and of palatine
(arrowheads, C) and lingual (curved arrows, D)
tonsils.
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Fig. 6C. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Axial 18FFDG
PET/CT images show normal 18FFDG uptake in lymphoid tissues of
nasopharynx (straight arrows, B), and of palatine
(arrowheads, C) and lingual (curved arrows, D)
tonsils.
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Fig. 6D. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Axial 18FFDG
PET/CT images show normal 18FFDG uptake in lymphoid tissues of
nasopharynx (straight arrows, B), and of palatine
(arrowheads, C) and lingual (curved arrows, D)
tonsils.
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Fig. 6E. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Coronal fused
18FFDG PET/CT images show normal 18FFDG uptake in
parotid (straight arrows, E and F), and submandibular
(curved arrows, E) salivary glands and vocal cords
(arrowheads, F).
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Fig. 6F. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Coronal fused
18FFDG PET/CT images show normal 18FFDG uptake in
parotid (straight arrows, E and F), and submandibular
(curved arrows, E) salivary glands and vocal cords
(arrowheads, F).
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Fig. 6G. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Coronal fused
18FFDG PET/CT image obtained in 60-year-old man shows
18FFDG uptake in hard palate mucosa (arrowhead) and
genioglossus muscle (arrows).
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Fig. 6H. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Axial fused
18FFDG PET/CT image obtained in 52-year-old man at nasopharyngeal
level shows normal 18FFDG uptake in right lateral pterygoid muscle
(arrow).
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Fig. 6I. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Coronal fused
18FFDG PET/CT image of neck in 41-year-old woman shows normal
18FFDG uptake in neck muscle (arrows) due to physical
activity after 18FFDG injection.
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Fig. 6J. —Fused PET/CT images in several patients depict areas of
normal 18FFDG uptake in head and neck. Axial 18FFDG PET
image obtained at level of parotid glands (arrows) in 57-year-old man
shows 18FFDG uptake in normal parotid gland with standardized
uptake value (SUV) of 4.78. Although SUV of normal parotid gland (and other
normal structures depicted in A–I) may be in malignant range,
symmetric distribution of 18FFDG uptake and typical locations of
physiologic uptake help in differentiation between physiologic and abnormal
metabolisms. Boxed area is region in which SUV was measured.
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Diagnosis and Initial Staging of Head and Neck Cancers with 18FFDG PET/CT
Accurate initial assessment of the primary site of head and neck cancers,
nodal involvement, and metastasis evaluation is crucial in staging, treatment
planning, and establishing the prognosis of patients with these cancers.
Although most primary malignancies of the oral cavity, larynx, and pharynx are
readily accessible for clinical examination and biopsy, clinical examination
often understages the extent of disease
[11]. Five percent of patients
with head and neck squamous cell carcinoma present with metastatic cervical
nodes without an identifiable primary site at clinical examination
[12,
13]. Also, evaluation of nodal
status may be limited by a patient's body habitus or lack of accessibility due
to the location of the node. Therefore, almost all patients with head and neck
cancers need some form of cross-sectional imaging for assessment of the extent
of disease.
18FFDG PET is superior to CT or MRI for detecting lymph node
metastasis, with sensitivity and specificity of approximately 90% and 94%,
respectively, as compared with 82% and 85% for CT, 80% and 79% for MRI, and
72% and 70% for sonography, respectively
[14]. However,
18FFDG PET has poor spatial resolution and cannot accurately assess
lymph node morphology, which is relevant for nodal staging. Number (single or
multiple), distribution (ipsilateral, contralateral, or bilateral), and lymph
node size (smaller than 3 cm, between 3–6 cm, and greater than 6 cm) are
all important for nodal staging of head and neck cancers. Although PET is
better for the assessment of metastasis in lymph nodes that appear
morphologically normal according to size criteria, CT is more accurate for
assessing the level and size of nodes (Fig.
7A,
7B), the number of nodes in
conglomerate nodal masses, and the presence of extracapsular
spread—factors that are important for determining the prognosis of
patients [15]; macroscopic
extranodal spread carries a 10 times greater risk of recurrence and reduces
survival by 50% compared with nodes that have either no or only microscopic
extracapsular spread. Also, intense 18FFDG uptake by the primary
tumor may obscure uptake by adjacent enlarged lymph nodes, thereby resulting
in false-negative results. Therefore, a combination of PET/CT is likely to
result in more accurate nodal staging than PET or CT alone. Size and local
extent of the primary tumor, which are important for staging, prognostication,
and treatment planning, are more accurately assessed on CT or MRI (Figs.
8A,
8B,
8C and
9A,
9B).
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Fig. 7A. —62-year-old man with metastatic squamous cell carcinoma of
neck evaluated on 18FFDG PET/CT for nodal staging. Axial image from
18FFDG PET portion of examination shows hypermetabolism
(arrows) in right supraclavicular region consistent with malignant
lymph nodes. However on PET alone, it is not possible to determine number and
size of nodes or presence of extracapsular tumor spread—information that
is important for staging and prognosis.
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Fig. 7B. —62-year-old man with metastatic squamous cell carcinoma of
neck evaluated on 18FFDG PET/CT for nodal staging. Axial
contrast-enhanced image from CT portion of examination obtained at same level
as A shows more than three nodes (arrowheads) in right
supraclavicular region, all smaller than 6 cm in greatest diameter with
extracapsular spread (arrow). Such findings aid in accurate staging
and prognostication.
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Fig. 8A. —59-year-old man with poorly differentiated laryngeal
carcinoma evaluated on 18FFDG PET/CT for local and nodal extent of
disease. Axial image from 18FFDG PET portion of examination shows
intense hypermetabolism (arrowheads) at site of primary tumor and
right neck, consistent with malignancy. However, local extent of primary tumor
cannot be evaluated on PET alone.
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Fig. 8B. —59-year-old man with poorly differentiated laryngeal
carcinoma evaluated on 18FFDG PET/CT for local and nodal extent of
disease. Axial contrast-enhanced CT (B) and fused 18FFDG
PET/CT (C) images show large laryngeal mass (arrowheads,
B and C) invading adjacent structures—hyoid bone (H,
B) and ipsilateral pyriform sinus—and crossing midline
(straight arrow, B). Large metastatic level 2a-III
jugulodigastric lymph node (N, B) is also seen at same level as
extracapsular spread (curved arrow B) and necrotic center
(focal central area of less intense 18FFDG uptake, C),
compressing adjacent internal jugular vein (IJV, B).
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Fig. 8C. —59-year-old man with poorly differentiated laryngeal
carcinoma evaluated on 18FFDG PET/CT for local and nodal extent of
disease. Axial contrast-enhanced CT (B) and fused 18FFDG
PET/CT (C) images show large laryngeal mass (arrowheads,
B and C) invading adjacent structures—hyoid bone (H,
B) and ipsilateral pyriform sinus—and crossing midline
(straight arrow, B). Large metastatic level 2a-III
jugulodigastric lymph node (N, B) is also seen at same level as
extracapsular spread (curved arrow B) and necrotic center
(focal central area of less intense 18FFDG uptake, C),
compressing adjacent internal jugular vein (IJV, B).
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Fig. 9A. —63-year-old man with nasopharyngeal squamous cell carcinoma;
advantage of fused 18FFDG PET/CT in evaluating local extent of
tumor. Axial image from 18FFDG PET portion of examination obtained
at level of nasopharynx shows focal hypermetabolism (arrowheads)
anteriorly at site of primary tumor. Evaluation of local invasion is not
possible on PET alone. Curved arrows mark normal 18FFDG uptake in
cerebellum.
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Fig. 9B. —63-year-old man with nasopharyngeal squamous cell carcinoma;
advantage of fused 18FFDG PET/CT in evaluating local extent of
tumor. Axial image from CT portion of examination obtained at same level as
A shows advanced nasopharyngeal cancer (arrowheads) with local
invasion of adjacent bones in skull base (arrowheads). Patient
thereafter underwent chemoradiation therapy.
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PET with 18FFDG has been shown to be able to reveal unknown
primary tumors in approximately 30–50% of patients with metastatic
disease to the lymph nodes in the neck who had no detectable primary tumor at
clinical examination [16]
(Figs. 10A,
10B,
10C and
11A,
11B,
11C), whereas CT and MRI in
combination with endoscopy and random biopsy of likely primary sites such as
tonsils, nasopharynx, and tongue base reveal the primary site in 10–20%
of these patients [13].
Because normal structures such as lymphoid tissue in the tonsils, tongue base,
and nasopharynx show variable physiologic activity, they may potentially
hinder detection of such unknown primaries. Abnormally high or asymmetric
18FFDG uptake helps in guiding direct examination and biopsy.
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Fig. 10A. —44-year-old woman with squamous cell carcinoma metastatic to
cervical lymph node and unknown primary site that was correctly identified on
18FFDG PET/CT. Coronal fused 18FFDG PET/CT image of neck
shows focus of increased uptake (arrowhead) in right neck
corresponding to metastatic level 2 lymph node.
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Fig. 10B. —44-year-old woman with squamous cell carcinoma metastatic to
cervical lymph node and unknown primary site that was correctly identified on
18FFDG PET/CT. Axial CT image obtained at level of oropharynx shows
mild asymmetry of tonsils with larger left tonsil (arrow)
contralateral to metastatic lymph node. Source: Kapoor V, McCook BM, Torok FS.
An introduction to PET-CT imaging. RadioGraphics
2004;24:523–543. Reprinted with permission.
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Fig. 10C. —44-year-old woman with squamous cell carcinoma metastatic to
cervical lymph node and unknown primary site that was correctly identified on
18FFDG PET/CT. Fused 18FFDG PET/CT image obtained at
same level as B shows asymmetric 18FFDG uptake with intense
hypermetabolism (arrows) in left tonsil that on biopsy was found to
be primary tumor site for contralateral metastatic nodal disease. Source:
Kapoor V, McCook BM, Torok FS. An introduction to PET-CT imaging.
RadioGraphics 2004;24:523–543. Reprinted with permission.
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Fig. 11A. —62-year-old man with extensive nodal and distant metastatic
disease from unknown primary tumor detected on fused 18FFDG PET/CT.
Axial contrast-enhanced CT image obtained at level of angle of mandible shows
multiple large necrotic metastatic (squamous cell carcinoma) level 1 and 2
lymph nodes (arrowheads) on right.
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Fig. 11B. —62-year-old man with extensive nodal and distant metastatic
disease from unknown primary tumor detected on fused 18FFDG PET/CT.
Corresponding axial fused 18FFDG PET/CT image shows hypermetabolism
in right cervical lymph nodes (arrowheads) and in right palatine
tonsil (arrows) that was found to be site of primary tumor at
biopsy.
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Fig. 11C. —62-year-old man with extensive nodal and distant metastatic
disease from unknown primary tumor detected on fused 18FFDG PET/CT.
Axial fused 18FFDG PET/CT image of thorax shows increased uptake in
right axillary (arrow) and hilar (arrowheads) lymph nodes
due to metastatic disease.
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PET/CT may also aid in the detection of a second primary tumor in patients
with head and neck carcinoma who are at an increased risk for synchronous or
metachronous carcinomas of the head and neck, esophagus, and lung (Fig.
12A,
12B). The risk of a second
primary tumor is approximately 4% per year, with 80% of the second primary
lesions located in the oral cavity, 40% in the larynx or pharynx, 31% in the
lungs, and 9% in the esophagus
[17]. Presence of distant
metastasis greatly affects the treatment (palliative vs curative) and
prognosis of patients with head and neck cancers. Metastasis to the lungs,
liver, and bones is likely in patients with advanced-stage and recurrent head
and neck cancer [12]. PET with
18FFDG has a sensitivity and specificity of 90% and 94%,
respectively, for detection of distant metastasis
[18] (Figs.
12A,
12B and
13A,
13B). In the presence of
distant metastases, palliative therapy would be more appropriate than
aggressive therapy.
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Fig. 12A. —56-year-old man with laryngeal squamous cell carcinoma and
second primary tumor in lung who underwent resection and radiation of
metastatic squamous cell carcinoma of lymph node from unknown primary tumor 4
years prior to this study. Coronal fused 18FFDG PET/CT image of
neck shows intense supraglottic hypermetabolism (arrows) consistent
with cancer (squamous cell cancer on biopsy) having transglottic spread.
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Fig. 12B. —56-year-old man with laryngeal squamous cell carcinoma and
second primary tumor in lung who underwent resection and radiation of
metastatic squamous cell carcinoma of lymph node from unknown primary tumor 4
years prior to this study. Axial fused 18FFDG PET/CT image of
thorax shows large right lower lobe lung mass (arrows) with
cavitation (arrowhead). Increased 18FFDG uptake is seen in
this mass that proved to be primary squamous cell carcinoma.
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Fig. 13A. —51-year-old man with primary anaplastic thyroid carcinoma
with metastatic nodal, liver, and bone disease. Coronal fused
18FFDG PET/CT image of neck shows intense hypermetabolism in large
mass in right thyroid lobe (arrows) and in metastatic ipsilateral
level 2 and 3 lymph nodes (arrowhead). C = clavicle, S = sternum.
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Fig. 13B. —51-year-old man with primary anaplastic thyroid carcinoma
with metastatic nodal, liver, and bone disease. Coronal fused
18FFDG PET/CT image of abdomen shows focal hypermetabolism in liver
(arrowhead) and L3 vertebral body (arrows) consistent with
metastatic disease. Vertebral lesion was not seen on CT alone (images not
shown). Curved arrow marks 18FFDG excretion into right renal
pelvis.
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Conclusion
Accurate initial staging is critical in the treatment of patients with head
and neck cancer. Although CT and MRI are superb cross-sectional imaging
techniques, 18FFDG PET/CT combines the excellent anatomic detail of
CT with metabolic activity data from 18FFDG PET in a single imaging
session, thereby increasing the accuracy of initial staging in these
patients.
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Introduction
Principle of 18FFDG PET/CT
