Thoracic Imaging 2003 - Society of Thoracic Radiology

THURSDAY
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from the laryngeal surface and rim of the epiglottis, aryepiglottic
folds, arytenoids, false cords, and laryngeal ventricles. They
commonly extend across the midline, invade the extralaryngeal
structures by direct extension to the pyriform sinuses, postcricoid
region and potentially extend to the cervical esophagus, valleculae,
and base of tongue. Vocal cord cancers arise commonly from
the anterior two-thirds of the vocal cords and may spread via the
anterior commissure to the subglottic space (20%) and infrequently
into the cervical trachea. Deep penetration of the cord by
tumor into the vocalis muscle causes fixation of the cord.
Carcinomas arising in the cervical trachea may involve by
superior extension the subglottic larynx. In larger carcinomas it is
often difficult to determine whether the origin is from the cervical
esophagus, the cervical trachea or an extension of a subglottic
carcinoma into the upper trachea. Stomal recurrence postlaryngectomy
is encountered in 5 to 15% of cases. The tumor
manifests as single or multiple nodules at or near the stomal margin
involving the skin or tracheal mucosa. Deep invasion is commonly
present associated with ulceration at the skin margin.
CT evaluation provides valuable information concerning
extension of malignant tumor to the following areas: 1) the anterior
commissure; 2) the paracordal and para-arytenoidal areas; 3)
the preepiglottic and subglottic spaces; 4) cartilage invasion; 5)
extralaryngeal extension of an endolaryngeal tumor and 6) extension
of pyriform sinus carcinomas through the cricothyroid space
to involve the postcricoid region and cervical esophagus. Contrast
CT or MRI is utilized to evaluate the tracheal extension and
tumor invasion of the upper mediastinum prior to surgery and/or
radiation therapy.
Trachea
Although very rare, primary malignancies of the trachea are
much more common than benign tumors. Squamous cell carcinoma
is the most common tracheal malignancy (50%), followed by
adenoid cystic carcinoma (30%), and adenocarcinoma (10%).
Other less frequently encountered malignancies include mucoepidermoid
carcinoma, undifferentiated carcinoma, small cell carcinoma,
and carcinosarcoma.
Squamous cell carcinoma
Squamous cell carcinoma may present as a focal mass with a
tendency for exophytic growth and a propensity to invade the
mediastinum. Synchronous and metachronous squamous cell
carcinomas of the larynx, lungs and esophagus are found in many
patients. CT is useful in demonstrating the primary tumor and its
extent in the trachea and adjacent mediastinum as well as associated
adenopathy within the mediastinum and hilum.
Adenoid cystic carcinoma
Adenoidcystic carcinoma tends to grow with endophytic
spread in the susbmucosal plane of the trachea and bronchi. On
radiographs, CT and MRI scans the trachea appears thickened
with a smooth nodular appearance, associated with luminal narrowing.
The tumor may extend into the adjacent soft tissues of
the neck and mediastinum, depicted on CT or MRI as extension
into the adjacent mediastinal fat. Regional lymph nodes in the
neck and mediastinum are the first to be involved by metastases.
Hematogenous metastases to lung, bones and liver do occur later
in the disease progression.
Mucoepidermoid tumors
Mucoepidermoid tumors are very uncommon tumors of the
trachea, central bronchi and rarely of the lung. They may be of
either high or low-grade malignancy. The radiographic findings
are of a focal endoluminal soft tissue mass within a large central
airway, without characteristic features to distinguish the mass
from other tumors.
Carcinoid tumors
Carcinoid tumors are neuroendocrine tumors derived from the
Kulchitski cell. Typical carcinoid tumor represents the lowest
grade subtype of a spectrum of tumors that includes the more
aggressive atypical carcinoid tumor and the highly malignant
small cell carcinoma. Typical carcinoids present in the fifth and
sixth decades and tend to arise in the central bronchi, peripheral
lung (10%) and rarely in the trachea. They tend to be smooth,
well-define round masses that present as a nodular filling defect
and may be associated with atelectasis, distal pneumonia, and/or
bronchiectasis if they cause bronchial obstruction. Atypical carcinoid
tumors tend to present in the sixth and seventh decades of
life, may be either central or peripheral in the lung and have a tendency
to metastasize to regional hilar and mediastinal lymph
nodes. Small cell carcinomas are extremely malignant tumors
that present in the seventh and eighth decades. They usually are
associated with large bulky central hilar and mediastinal lymphadenopathy
and distant metastases at the time of diagnosis. CT
scans often reveal a small peripheral primary tumor within the
lung, generally not visible on routine chest radiographs.
Carcinoid tumors have several distiguishing features on imaging
studies. Typical carcinoid tumors generally exhibit slow
growth and may contain calcifications. Carcinoid tumors are
highly vascular and will demonstrate a high degree of contrast
enhancement with iodinated contrast on CT scans. Because
somatostatin receptors are found in carcinoid tumors, radionuclide-coupled
somatostatin analogues such as 123-I-Tyr3octreotide
and 111-In-octreotide can be used to identify carcinoid
tumors. This diagnostic approach is helpful in identifying occult
carcinoid tumors in those patients who present with clinical
symptoms referable to seratonin, ACTH or bradykinin production.
Mesenchymal tumors
Mesenchymal tumors are rarely reported to occur in the trachea,
and tend to occur in young adults. Fibrosarcoma,
leiomyosarcoma, chondrosarcoma, hemangioendotheliosarcoma,
and lymphomas have been reported. Except for calcifications in
the chondrosarcomas, there are no specific characteristics with
which to differentiate mesenchymal tumors from other malignancies.
Secondary malignant tumors
Carcinomas especially papillary and follicular types arising
from the thyroid gland may invade the larynx and cervical trachea
in up to 5% of cases. The trachea may also be invaded by tumors
of the esophagus and lung. The delineation of the extent of these
tumors is best accomplished with CT and MRI.