AJR 2004; 183:277-281
© American Roentgen Ray Society
Adenoid Cystic Carcinoma of the Airways:Helical CT and Histopathologic Correlation
Seo-Hyun Kwak1,
Kyung Soo Lee1,
Myung Jin Chung1,
Yeon Joo Jeong1,
Gou Young Kim2 and
O Jung Kwon3
1 Department of Radiology and Center for Imaging Science, Samsung Medical
Center, Sungkyunkwan University School of Medicine, 50, Ilwon-dong Kangnam-gu,
Seoul 135-710, Korea.
2 Department of Diagnostic Pathology, Samsung Medical Center, Sungkyunkwan
University School of Medicine, Seoul 135-710, Korea.
3 Department of Medicine, Division of Pulmonary and Critical Care Medicine,
Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul
135-710, Korea.
Received December 10, 2003;
accepted after revision February 17, 2004.
Supported in part by grant R11-2002-103 from the Korea Science &
Engineering Foundation.
Address correspondence to K. S. Lee
(melon2{at}samsung.co.kr).
Introduction
Primary tumors of the trachea are rare and constitute only 2% of all
respiratory tract tumors [1].
Of these, malignant tumors are more common than benign tumors and account for
60–83% in adults [2].
Adenoid cystic carcinoma, which was formerly named "cylindroma"
and "adenocystic carcinoma," occurs mainly in the salivary glands
or central airways, such as the trachea and the main bronchi; it is a
low-grade malignancy that is the second most common tracheal malignancy at
histology (33%) after squamous cell carcinoma (48%)
[3].
With the advent of MDCT, rapid scanning throughout the thorax and
multiplanar reconstruction without loss of z-axis information are
possible; therefore, visualization of the airways has become easier. The
purpose of this pictorial essay is to describe the helical CT findings of
adenoid cystic carcinomas of the airways and to correlate these findings with
the histopathology.
Clinical Findings
Adenoid cystic carcinomas are usually first recognized without sex
predilection in patients in their 40s
[4], and smoking does not
affect the incidence [5].
Symptoms in patients with adenoid cystic carcinoma are usually related to
airway obstruction. Dyspnea, cough, stridor, wheezing, and hemoptysis are the
most common complaints. Unfortunately, these signs and symptoms often lead to
a misdiagnosis as asthma or bronchitis. Recognizing adenoid cystic carcinoma
is important because patient prognosis is improved with early treatment
[6].
Radiographic and Helical CT Findings
Adenoid cystic carcinomas usually arise in the lower trachea (Figs.
1A,
1B,
1C and
2A,
2B,
2C). Others are found in the
mainstem bronchi (Figs. 2A,
2B, and
2C); lobar bronchi (Figs.
3A,
3B and
4A,
4B,
4C); or, rarely, in the
segmental bronchi (Figs. 5A,
and 5B) and extrathoracic
trachea (Figs. 6A,
6B, and
6C).
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Fig. 1A. —Adenoid cystic carcinoma in 33-year-old man. Unenhanced
transaxial CT scan (2.5-mm collimation) obtained at level of thoracic inlet
shows tracheal tumor of irregular contour and broad base with both
intraluminal (arrow) and extraluminal (arrowheads)
components. More than 180° of tracheal circumference is involved.
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Fig. 1B. —Adenoid cystic carcinoma in 33-year-old man. Sagittal
reformatted image (2.5-mm thickness) shows both intraluminal (arrow)
and extraluminal (arrowheads) components of tracheal tumor and
longitudinal extent of lesion.
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Fig. 1C. —Adenoid cystic carcinoma in 33-year-old man. Photomicrograph
of transaxial section of gross specimen shows intraluminal (arrows)
and extraluminal (arrowheads) components of tumor. (H and E,
x1)
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Fig. 2A. —Adenoid cystic carcinoma in 60-year-old man. Unenhanced
transaxial CT scan (3-mm collimation) at level of distal trachea that was
obtained using mediastinal window settings shows lobulated and broad-based
intraluminal soft-tissue tumor (arrow) in anterolateral aspect of
distal trachea. Also note marked wall thickening (arrowheads). More
than 180° of circumference is involved.
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Fig. 2B. —Adenoid cystic carcinoma in 60-year-old man. Coronal
reformatted CT scan (2.5-mm thickness) shows both intraluminal and
extraluminal (arrowheads) growth of tumor. Longitudinal extent of
lesion involving distal trachea (solid arrow) and right main bronchus
(open arrow) is clearly visualized.
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Fig. 2C. —Adenoid cystic carcinoma in 60-year-old man. Photomicrograph
of longitudinal section of gross surgical specimen shows intraluminal
(arrows) and extraluminal (arrowheads) tumor growth
(predominantly, intraluminal growth) with multisegmental involvements of
tracheal cartilage. (H and E, x1)
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Fig. 3A. —Adenoid cystic carcinoma in 41-year-old man. Coronal
reformatted image of enhanced CT scan (2.5-mm thickness) shows soft-tissue
mass (arrow) obliterating right upper lobar bronchus and attendant
atelectasis of right upper lobe (arrowheads).
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Fig. 3B. —Adenoid cystic carcinoma in 41-year-old man. Enhanced
transaxial CT scan (2.5-mm collimation) obtained at level of liver dome shows
metastatic lesions (arrows) in liver. Metastases were proven with
percutaneous liver biopsy.
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Fig. 4A. —Adenoid cystic carcinoma in 40-year-old man. Enhanced
transaxial CT scan (2.5-mm collimation) obtained at level of left inferior
pulmonary veins shows soft-tissue lesion (arrow) encircling bronchus
intermedius. Right lower lobe (arrowhead) is partially
atelectatic.
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Fig. 4B. —Adenoid cystic carcinoma in 40-year-old man. Coronal
reformatted CT image (2.5-mm thickness) shows longitudinal extent of lesion
(arrows) encircling bronchus intermedius. Right lower lobe
(arrowhead) is partially atelectatic.
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Fig. 4C. —Adenoid cystic carcinoma in 40-year-old man. Photomicrograph
of longitudinal section of bronchus intermedius shows intraluminal growth of
tumor (arrows), obliterating distal bronchial lumen of bronchus
intermedius. (H and E, x1)
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Fig. 5A. —Adenoid cystic carcinoma in 43-year-old man. Enhanced
transaxial CT scan (2.5-mm collimation) obtained at level of middle lobe
bronchus shows soft-tissue tumor (arrow) filling lingular segmental
bronchus.
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Fig. 5B. —Adenoid cystic carcinoma in 43-year-old man. Photomicrograph
of transaxial section of gross surgical specimen shows transluminal tumor with
predominantly extraluminal growth pattern (arrows). L = bronchial
lumen. (H and E, x1)
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Fig. 6A. —Adenoid cystic carcinoma in 50-year-old woman. Enhanced
transaxial CT scan (5.0-mm collimation) obtained at level of thyroid glands
shows lobulated and broad-based soft-tissue lesion (arrows) in right
posterolateral portion of trachea with both intraluminal and extraluminal
components. Less than 180° of circumference is involved.
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Fig. 6B. —Adenoid cystic carcinoma in 50-year-old woman. Parasagittal
reformatted CT image (5.0-mm thickness) shows longitudinal extent of lesion
(arrow) mainly located in posterior portion of trachea.
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Routine posteroanterior and lateral chest radiographs are usually
interpreted as showing normal findings
[7]; however, intraluminal
filling defect with irregular, smooth, or lobulated contours may be identified
on radiographs. In addition, the extraluminal component may be visualized if
it is large enough to distort the normal mediastinal contour
[8].
For the adequate evaluation of the airways on helical CT, imaging
parameters of 1- to 3-mm section thickness, 1- or 2-mm reconstruction
increment, total active detector length pitch of 1.3–1.5, 120 kVp, and
180–250 mA are used [9].
Using these image data sets, transaxial images, multiplanar reconstruction
images, volume- and surface-rendered 3D images are acquired.
On CT, the tumor has a striking tendency toward submucosal extension that
manifests as an intraluminal mass of soft-tissue attenuation with extension
through the tracheal wall (Figs.
1A,
1B,
1C,
2A,
2B,
2C, and
6A,
6B,
6C), a diffuse or
circumferential wall thickening of the trachea, a soft-tissue mass filling the
airway (Figs. 3A,
3B,
4A,
4B,
4C,
5A, and
5B), or a homogeneous mass
encircling the trachea with wall thickening in the transverse and longitudinal
planes [10,
11]. The longitudinal extent
of the tumor is greater than its transaxial extent
[4] (Figs.
1A,
1B,
1C,
4A,
4B,
4C, and
6A,
6B,
6C). The tumors usually
involve more than 180° of the airway circumference (Figs.
1A,
1B,
1C and
2A,
2B,
2C). They are variable in
shape: polypoid (Figs. 5A, and
5B) or broad-based (Figs.
1A,
1B,
1C,
2A,
2B,
2C,
4A,
4B,
4C, and
6A,
6B,
6C). Their margins are also
variable: smooth (Figs. 5A,
and 5B), lobulated (Figs.
2A,
2B,
2C and
6A,
6B,
6C), or irregular (Figs.
1A,
1B, and
1C). Calcification within tumor
is rare [10,
11].
Although the most common site of the tumor in the trachea has been reported
to be the posterolateral wall (Figs.
6A,
6B, and
6C), the anterolateral wall
(Figs. 1A,
1B, and
1C)—near the junction of
the cartilage and the soft membranous parts of the trachea where mucous glands
are most plentiful—may also be a common site of involvement
[10,
11].
Adenoid cystic carcinoma in the extrathoracic trachea may directly invade
the thyroid gland and tracheal cartilages
[6]. Distant metastasis occurs
late in the disease course (Figs.
3A and
3B). Metastasis to the regional
lymph nodes may be present in up to 10% of primary tumors at the time of
diagnosis [7]. With the tumor
in the lobar or segmental bronchus, distal atelectasis (Figs.
3A,
3B and
4A,
4B,
4C) or obstructive pneumonitis
may be present. Air trapping may also be present.
Pathologic Findings
Grossly, adenoid cystic carcinoma is usually smooth, firm, and well
circumscribed (Figs. 1A,
1B, and
1C). It may present as an
exophytic lesion (Figs. 5A,
and 5B), often with poorly
defined margins (Figs. 2A,
2B, and
2C). The surface of the tumor
may be smooth or ulcerated. A bulky extratracheal mass may often be seen, and
direct invasion of the thyroid gland does occur
[7].
Microscopically, adenoid cystic carcinomas contain sheets of small uniform
cells arranged in a classic cribriform growth pattern (Figs.
6A,
6B, and
6C) or in a tubular pattern. A
solid component without cystic spaces is reported to be associated with more
locally aggressive tumors, which exhibit a tendency to spread submucosally
along perineural spaces or along the perineural lymphatics
[7].
CT–Pathologic Comparisons
Spizarny et al. [10]
expressed a concern that CT is a poor indicator of tumor longitudinal extent
and mediastinal organ invasion. However, with the use of helical CT data sets,
multiplanar reconstructions have been shown to facilitate the assessment of
patients with airway disease and are known to provide various advantages in
terms of image quality [12].
The reformatted images help to assess both the intra- and extraluminal growth
of the tumor and its longitudinal extent along the tracheal or bronchial wall
by allowing the evaluation of extraluminal surrounding tissues (Figs.
1A,
1B,
1C,
2A,
2B,
2C,
4A,
4B,
4C, and
6A,
6B,
6C). Therefore, helical CT
provides precise information about the extent of a tumor, which is important
for planning a surgical resection. Tumor sizes and growth patterns and the
presence of pulmonary parenchymal involvement identified on CT correspond to
those seen at pathology [12].
However, helical CT is still a poor predictor of microscopic mediastinal fat
or neural invasion [10].
In summary, adenoid cystic carcinomas, which are usually located in the
intrathoracic distal trachea, tend to exhibit longitudinal extension and both
intra- and extraluminal growth on helical CT. These findings correlate with
the histopathologic findings in most patients. In many cases, CT can be used
to assess the tumor extent and growth patterns.
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Introduction
Clinical Findings
