diagnostic imaging pediatric chest ct 1

7/29/2019 Diagnostic Imaging Pediatric Chest CT 1

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Pediatric Chest CT 1 - Nonvascular

Mediastinal MassesMarilyn J. Siegel and Valerie NieheMallinckrodt Institute of Radiology

Washington University School of MedicineSt. Louis, MO and the Medical CentreHaaglanden in the Hague, the Netherlands

Differential diagnosis

The differential diagnosis of a mediastinal

mass is based on identifying its location inanterior, middle or posterior mediastinum

and attenuation: soft tissue, fat, fluid andenhancement.

Normal AnatomyThymusIn infants and young children ( In older

children, the thymus gradually assumes atriangular or arrowhead configuration withstraight or concave margins.

By 15 years of age it is triangular in nearly allindividuals. Marked lobularity of the thymusis always abnormal.

In prepubertal children, the thymus is

homogeneous. The attenuation value isequal to that of skeletal muscle.

In adolescents it may be heterogeneous,containing areas of fat.

Anatomic variations include extension intothe posterior mediastinum or upper neck.Clues to the diagnosis are:

No mass effect

Contiguous with normal thymus

Extends between superior vena cava andtrachea

The figure shows a thymus that extendscranially to the brachiocephalic vessels. It iscontiguous with the normal thymus andextend between the superior vena cava andthe trachea. There is no mass effect.

Normal Lymph Nodes

There are no well-established dataconcerning size of normal lymph nodes ininfants and young children.


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Mediastinal lymph nodes are generally not

seen on CT prior to puberty.

The nodes should then not exceed 1 cm in

the widest dimension.The azygoesophageal recess isdextroconvex in children younger than 6years of age, straight in children between 5and 12 years of age, and concave inadolescents and adults.

Recognizing the normal dextroconvexappearance is important so that it is not

mistaken for lymphadenopathy.

Anterior Mediastinal Masses

Anterior mediastinal masses are usually ofthymic origin.

Hodgkin Lymphoma

Lymphoma is the most common anterior

mediastinal mass in children, with Hodgkinlymphoma occurring three to four times morefrequently than non-Hodgkin lymphoma.

Calcifications or cystic areas, due to

ischemic necrosis consequent to rapid tumorgrowth, can be seen.

Lymphadenopathy from lymphoma hasvaried appearances, ranging from mildlyenlarged nodes in a single area to largeconglomerate soft tissue masses in multiple

regions.

Thymic enlargement and lymphadenopathyshow minimal if any enhancement afterintravenous contrast.

Additional findings include airway narrowingand compression of vascular structures.

Hodgkin lymphoma in children is morecommon in the second decade of life.

The lymphomatous mass is most commonlocated in the anterior mediastinum andreflects lymphadenopathy or infiltration and

enlargement of the thymus.The enlarged thymus has a quadrilateral

shape with convex, lobular lateral borders.

The chest film shows the typical features ofHodgkin lymphoma, e.g., an anteriormediastinal mass.

The CT-images of the same patient show a

large soft tissue mass in the anteriormediastinum, which arises in thethymus. There is associated paratracheal

adenopathy (arrow).

Two more cases of Hodgkin lymphoma.

Again these cases show an anteriormediastinal mass and paratracheal

adenopathy.


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Non-Hodgkin lymphomaNon-Hodgkin disease in children occurs inthe first and second decade of life. The

disease usually involves the nodes in thechest (paratracheal, subcarinal and hilar).The extension of the disease is notcontiguous, it can skip a location.

Non-Hodgkin disease, in contrast to Hodgkindisease, often spares the thymus. In this

case, enlarged lymph nodes are seen in theright paratracheal , hilar and subcarinalareas.

Thymic Hyperplasia

Thymic hyperplasia is another cause ofthymic enlargement.

In childhood, thymic hyperplasia is most

often 'rebound' hyperplasia associated with

chemotherapy, particularly therapy withcorticosteroids.

Rebound hyperplasia may be observedduring the course of chemotherapy or aftertherapy completion and occurs 3 to 10months after the start of chemotherapy.

The mechanism of hyperplasia is believed tobe initial depletion of lymphocytes from thecortical portion of the gland due to high

serum levels of glucocorticoids, followed byrepopulation of the cortical lymphocyteswhen the cortisone levels return to normal.

On CT, hyperplasia appears as diffuseenlargement of the thymus, with preservation

of the normal triangular shape.

The definition of thymic hyperplasia is a > 50% increase in volume of the thymus.

CT, MRI of PET cannot differentiate reboundhyperplasia from infiltration of the thymus by

tumor.

The absence of other active disease and a

gradual decrease in thymus size on serialCT's supports the diagnosis of reboundhyperplasia.

The thymus usually returns to its normal size

in 3 to 6 months.

Thymoma

Thymomas are common and account for20% of mediastinal neoplasms. Thymic


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carcinomas are extremely rare and acount

for less than 1% of all thymic tumors.The images show a thymoma on the left anda carcinoma on the right. The thymic

carcinoma has invaded the superior venacava (arrow).

Germ-cell tumors

Germ-cell tumors are the most commoncause of a fat containing lesions in theanterior mediastinum and the second mostcommon cause of an anterior mediastinalmass in children.

Approximately 90 % are benign germ-cell

tumors. Most arise in the thymus.

On CT, a benign teratoma is a well-defined,

thick-wall cystic mass containing a variablemixture of water, calcium, fat and soft tissue.

The soft tissue component in benignteratoma is minimal. Size is not an indicatorof malignancy.

Mature teratomas can be very large and stillbe benign.

Malignant teratomas make up 10% of all

teratomas.

They tend to have irregular or nodular walls

and a predominance of soft tissuecomponents.

They also may show pulmonary or livermetastases and chest wall invasion.

The most common nonteratomatous germ-cell tumors in the pediatric population arechoriocarcinoma, embryonal cell cancer andyolk-sac cancer.

Thymolipoma

Thymolipoma is an infrequent fat-containingthymic tumor.

At CT, it appears as a heterogeneous mass

containing fat and soft tissue elements.Calcifications are absent.

Thymolipoma does not have a capsule anddoes not have any mass effect.

Lymphangioma or Cystic hygroma

Lymphangiomas are developmental tumorsof the lymphatic system.

In the mediastinum they are almost alwaysan inferior extension of a cervical

lymphangioma. Isolated mediastinalinvolvement is rare.

Lymphangioma is a benign, but aggressivetumor that shows mass effect and mayencase vessels and other structures.


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It typically affects infants younger than 6months of age.

At CT it appears as nonenhancing, thin-walled, multiloculated mass with near waterattenuation.

MRI may sometimes be used to betterdelineate the extension of the lesion.The MRI in this patient shows a cystic massin the neck extending into the right axilla andmediastinum.

The tumor encases vessels.

The presence of contrast enhancement ofthe wall or internal septations suggestssuperimposed infection or ahemangiomatous component.

T2 w/ Fat suppresion, transversal andcoronal

Thymic cysts

Thymic cysts are usually congenital lesionsresulting from persistence of thethymopharyngeal duct.

They can also occur after thoracotomy.

Typically, they are thinwalled, homogeneousmasses of near water attenuation on CT.

The attenuation value may be higher than

that of simple cysts when the contents areproteinaceous or hemorrhagic rather thanserous.

In children thymoma, thymic carcinoma and

goiter are so uncommon, that you should putthem very low in your differential diagnosis.

Middle Mediastinal Masses

In the middle mediastinum we will findforegut duplication cysts or lymph nodes.

Foregut cysts in the middle mediastinum areclassified as bronchogenic or enteric.

Bronchogenic cysts are lined by respiratoryepithelium and most are located in the

subcarinal or right paratracheal area in closeproximity to the trachea or bronchus.

Enteric cysts are lined by gastrointestinalmucosa and are located in a paraspinal


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position in the middle to posterior

mediastinum near the esophagus.

Bronchogenic Cysts

The images show a well defined lesion of

water attenuation in close proximity to thetrachea or bronchus, which is typical for abronchogenic foregut cyst.

The images show more examples ofbronchogenic cysts and their close proximityto the airway.

Enteric Foregut

The images show a well defined lesion ofwater attenuation in the lower mediastinum

in close proximity to the esophagus, which istypical for an enteric foregut cyst.

Mediastinal Lymphadenopathy

Mediastinal lymphadenopathy is usuallycaused by lymphoma or granulomatousdisease.

Metastatic disease from rhabdomyosarcoma,

osteosarcoma or a Wilms tumor, is also a

possibility.

On CT, adenopathy can appear as discrete,round, soft tissue masses or as a single softtissue mass with poorly defined margins.

Calcification within lymph nodes suggestsold healed granulomatous disease, fungal

infection or metastatic disease fromosteosarcoma.

Areas of low attenuation suggest

tuberculosis or fungal infection.

Posterior Mediastinal Masses

Posterior mediastinal masses are of neural

origin in approximately 95 % of cases and


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may arise from sympathetic ganglion cells

(neuroblastoma, ganglioneuroblastoma organglioneuroma) or from nerve sheaths(neurofibroma or schwannoma).

Neuroblastoma

Neuroblastoma typically is fusiform in shape,of soft tissue density; 50% of thoracic tumorshave calcifications.

Neuroblastoma presenting as a mass in theposterior mediastinum

Neuroblastoma grows over severalinterspaces and frequently invades the

vertebral canal.

The CT-images show a calcified mass in theposterior mediastinum extending overseveral vertebrae, which grows into the

vertebral canal.

On the MR-images the invasion of thevetebral canal is better seen (arrows).

Other Neurogenic Tumors

In the 2nd decade other neurogenic tumorsare seen like ganglioneuroma, neurofibromaand rarely schwanoma. They are round or

oval in shape, smaller in size than ganglioncell tumors and usually extend over only one

or two vertebrae.

Both types of tumor may cause pressureerosion of a rib and invade the spinal canal.

LEFT: Ganglioneuroma, RIGHT:Neurofibroma


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Neurenteric Cyst

Neurogenic cysts contain neural andgastrointestinal element.

They are commonly associated withvertebral anomalies and scoliosis. The cystdoes not communicate with CSF.

The cyst is well demarcated and has a nearwater attenuation value on CT and water

signal intensity on MRI, as shown in the caseon the left.

Extramedullay Hematopoiesis

Extramedullary hematopoiesis accounts forless than 0.1 % of the lesions in the posteriormediastinum.It is characterized by formation of blood

elements outside of the bone marrow. Itoccurs with severe anemia.

On CT it is seen as a paravertebral massand occurs with coarse bone trabeculation inthe adjacent vertebra.

Extramedullary hematopoiesis masses in the

paraspinal area and adjacent to the sternum.

End.

Source:http://www.radiologyassistant.nl/en/p4de672

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diagnostic imaging pediatric chest ct 1

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