Mediastinum: The Hilum

10.1055/b-0034-87854

Mediastinum: The Hilum

The hilum encompasses the root of the lung and consists of the major pulmonary vessels, bronchial walls, and lymph nodes. Hilar enlargement in children may be due to a general increase in hilar markings, usually reflecting peribronchial thickening such as occurs in viral lower respiratory tract infection, CF, and asthma. True hilar enlargement represents either hilar lymphadenopathy or hilar pulmonary arterial enlargement. Adenopathy is characterized by a lobulated outline to the hilum, often with filling in of the hilar point at the junction of the superior pulmonary vein with pulmonary artery. Arterial enlargement demonstrates retained vascular contours, often with a dilated main pulmonary artery. Distinction between arterial enlargement and adenopathy is best achieved with cross-sectional imaging.

In children, the lymph nodes will only be seen if they are enlarged and thus pathologic in size. For a detailed evaluation of the hilum, contrast-enhanced CT or MRI should be used.

Although the hilum can be visualized on the lateral film, it is not common practice to obtain routine lateral films in children; as radiation protection, this is essential (image gently).

**Table 1.54 Bilateral hilar enlargement due to lymphadenopathy**
Diagnosis	Findings	Comments
Bronchiolitis, reactive airway disease (RAD), viral infections of the lower airways Fig. 1.146a, b	Minimal interstitial prominence, peribronchial thickening, hyperinflation (especially in viral infections). The hilar lymph nodes are increased in size rather than density; the outline is hazy.	Episodes of coughing, possibly febrile, signs of infection. Seasonal occurrence of RSV infections, mainly in autumn and winter.
Measles	Hila are dense, with prominent bronchovascular markings. In the exanthematous phase of measles pneumonia, the hila are widened and more dense, and lung markings are increased; miliary nodules are also present adjacent to the hila.	Nowadays rare as a result of vaccination programs.
Pertussis	The increased dense hilar markings and perihilar signs (“shaggy heart”) reflect bronchitis in the cartarrhal stage. Increased pulmonary density occurs mainly in the basal segments.	Diagnosed by the typical episodes of coughing in the convulsive stage, previously known as “catarrhal bronchitis.”
CF Fig. 1.147	Densely enlarged hila, initially moderate and increasing over ensuing years. Increasing pulmonary involvement with chronic infilitrative changes. Secondary hyperinflation and barrel chest deformity. Late findings resemble bronchiectasis.	Onset in infancy, increasing and progressing in childhood. All signs of chronic infection with dyspnea and cough.
Malignant lymphoma/leukemia Fig. 1.148a–c Fig. 1.149a–c, p. 86 Fig. 1.150, p. 86	Neoplastic mediastinal enlargement is mostly due to bilateral lymph node enlargement, particularly the paratracheal nodes.	Diagnosed on bone marrow biopsy. Hematologic changes. Peripheral lymphadenopathy, hepatosplenomegaly. Bruises. Hilar involvement in Hodgkin disease in 50%, more common than in NHL.
Mycoplasma infection	Hilar enlargement accompanied by segmental pneumonia, particularly in the lower lobes (may even be unilateral). Radiographic appearance commonly resembles TB.	Mild leucocytosis or normal white cell count. Organism must be positively proven. Bronchoalveolar lavage.
LCH, malignant histiocytosis	Mild, rarely marked hilar enlargement with sharp outlines. Evolves into interstitial pulmonary changes with small patches and confluent densities mainly in the bases. Emphysematous blebs, honeycomb lungs.
Chronic aspiration	Combination of bilateral hilar enlargement with multiple disseminated small patchy pulmonary densities.
Fungal infection	May be unilateral. Perihilar and occasional mediastinal lymph node involvement. Caution: air-space disease.
TB Fig. 1.151, p. 86	Nodular density to increasing hilar width. Primary complex in the lungs. Loss of the mediastinal contour.	Small children to young school age. Gradual onset, with or without cough. Rarely febrile. Purified protein derivative (PPD) positive. May also be asymptomatic. Increasingly seen in the western world after a period of relevant low incidence.
Bacterial pneumonia	In association with bilateral air space disease. Unlikely under 18–24 mo as mother’s antibodies still present.	Clinical signs of pneumonia.
Castlemann disease	May involve single or multiple mediastinal compartments, including the hila.	A group of rare lymphoproliferative disorders that are more common in adults.
Sarcoidosis Fig. 1.152a, b, p. 87	Characteristically symmetric lobulated lymph nodes; no pulmonary changes in stage 1, later (stage 2) there are small patchy densities in the lungs. Other lymph nodes can also become involved (tracheobronchial, paratracheal).	This classic adult presentation is extremely rare in preteenaged children.
Vascular causes: increased hilar and pulmonary vascular markings—active: left-to-right shunt	Enlarged hila with enlarged vessel caliber.	(see Table 1.75 )
Specific type: pulmonary hypertension	Pulmonary arteries are significantly enlarged close to the hilum, and constricted peripherally (“arterial pruning”).
Vascular causes: increased hilar and pulmonary vascular mark-ings—passive: cardiac failure	Enlarged hila and increased caliber of the vessels that are hazy in outline.
Vascular causes: increased hilar and pulmonary vascular mark-ings—pulmonary valve failure	Massively enlarged hila, with decreased peripheral pulmonary vascular markings.	Rare, most commonly in tetralogy of Fallot (see Table 1.78 ).
Metastases	Neoplastic in nature, lobulated or egg-shaped lymph nodes.
Granulomatous infections	More usually unilateral.	TB, histoplasmosis.
Other infections	Milder hilar enlargement can occur in many acute and chronic pulmonary infections.	Examples include RSV (often more right-sided), pertussis (now rare), chicken pox, measles, myco-plasma, bacterial pneumonia.

**Fig. 1.146a, b Bronchiolitis.** (a) Bronchiolitis in a 20-month-old boy. (b) Lateral chest radiograph shows flattening of the diaphragm.

**Fig. 1.147 Bilateral hilar enlargement in cystic fibrosis.**

**Fig. 1.148a–c Lymphoma.** (a) Bilateral hilar enlargement in a 16-year-old girl with lymphoma. (b) PET-CT of the same patient shows the extent of disease. (c) PET-CT of the same patient.

**Fig. 1.149a–c Lymphoma.** (a) Bilateral hilar enlargement in a 16-year-old girl with lymphoma. (b) Whole-body STIR MRI shows pathologic lymph node enlargement. (c) Diffusion-weighted whole body imaging with background signal suppression, a new diffusion-weighted imaging technique for whole body imaging that produces PET-like images.

**Fig. 1.150a, b Hodgkin disease.** (a) Chest radiograph in an 8-year-old boy with cervical lymphadenopathy and night sweats. There is right paratracheal lymphadenopathy causing some tracheal displacement (black arrow). There is also right hilar enlargement (white arrow). (b) Coronally reformatted CT in the same patient demonstrates adenopathy as described, but with further lymph node enlargement in the subcarinal (white arrow) and left hilar stations (black arrow). Lymph node biopsy confirmed Hodgkin disease.

**Fig. 1.151 Bilateral hilar enlargement** in a 16-year-old boy.

**Fig. 1.152a, b Sarcoidosis.** (a) Stage 2 sarcoidosis. (b) CT of the same patient shows interstitial abnormalities.

**Table 1.55 Bilateral hilar enlargement due to pulmonary arterial dilatation**
Diagnosis	Findings	Comments
Left-to-right shunt Fig. 1.153	Cardiac enlargement with VSD and PDA. Right atrial enlargement only in ASD.	ASD, VSD, PDA, AVSD.
Primary pulmonary hypertension	Large central vessels, “pruned” peripheral vessels.	Rare, idiopathic condition with poor prognosis. Familial and sporadic forms. Presentation with dyspnea and chest pain.
Chronic pulmonary disease	Usually evidence of underlying lung disease.	CF most common. Also BPD, interstitial fibrosis, pulmonary hypoplasia.
Pulmonary valve regurgitation	Often massive pulmonary arterial dilatation, may cause airway obstruction.	Usually as a variant of tetralogy of Fallot (“absent pulmonary valve syndrome”).
Recurrent pulmonary emboli		Rare in children. Usually line associated (e.g., children on total parenteral nutrition).
Pulmonary venous abnormality Fig. 1.16, p. 14	Mixed arterial and venous dilatation, with or without frank pulmonary edema.	Examples include anomalous venous return, pulmonary vein stenosis, pulmonary veno-occlusive disease, left atrial obstruction.

**Fig. 1.153 Massive pulmonary arterial dilatation.** Chest radio-graph in a 14-year-old female with Eisenmenger syndrome. There is massive dilatation of the main and central pulmonary arteries, with relatively oligemic lung periphery.

**Table 1.56 Unilateral hilar enlargement due to lymphadenopathy**
Diagnosis	Findings	Comments
Nonspecific upper or lower respiratory tract infection (bronchiolitis) Fig. 1.154 Fig. 1.155	Peribronchial thickening, increased pulmonary vascular markings. Effacement of the mediastinal contour at the level of the hilum, more commonly bilateral.	Fever, cough, wheezing.
TB (primary infection)	Nodular density leads to increasing hilar size. Primary complex in the lungs. Loss of the mediastinal contour. Usually right-sided. Often associated subcarinal ± paratracheal lymphadenopathy. May cause air t rapping or collapse (see Fig. 1.17c ). Rim enhancement with low central density on CT. Calcification rare in primary infection. Primary focus may or may not be visible.	Small children to young school age. Gradual onset, with or without cough. Rarely febrile. PPD positive. May also be asymptomatic.
Other granulomatous infection		Histoplasmosis, coccidioidomycosis.
Bacterial, mycoplasma, and fungal pneumonias	Disease correlates with the radiographic appearance. Unilateral more common than bilateral.	Signs of acute infection, cough, moderate dyspnea.
Viral pneumonia Fig. 1.156	Pulmonary changes are the same as described with bilateral viral pneumonia. Rarely unilateral.	Cough, signs of infection.
Metastases	Unilateral, moderately well defined, hilar lymphadenopathy; confirmed on the lateral radiograph.
Malignant lymphoma/leukemia Fig. 1.157	Mostly with other signs of lymphoma (mediastinal, paratracheal, bronchial), effusions. Bilateral hilar enlargement far more common.	Signs of systemic illness.
Infectious mononucleosis Fig. 1.158	Unilateral or bilateral. No pulmonary changes.	Serologic proof of the specific Epstein-Barr viral antibodies.
Pertussis		(see Table 1.50 )
Vascular causes: unilateral enlargement of the pulmonary artery
Absent pulmonary valve with unilateral agenesis of the pulmonary artery	Marked widening of one hilum, mainly the right, with a very small left hilum. Very rare variant of tetralogy of Fallot.
Valvular pulmonary stenosis	Widened left hilum and pulmonary artery segment.	(see Table 1.76 )

**Fig. 1.154 Pneumonia with unilateral hilar enlargement** in a 9-year-old girl.

**Fig. 1.155 Unilateral hilar adenopathy in TB.** Chest radiograph in a 14-year-old Arabic girl with TB isolated from a lymph node biopsy. There is left hilar (white arrow) and aortopulmonary (black arrow) lymphadenopathy. There is some ill-defined left lower lobe opacification and a small left-sided pleural effusion. An apparent lobulated mass overlying the left clavicle (circled) was a hair braid artifact.

**Fig. 1.156 RSV pneumonia** in a 20-month-old boy.

**Fig. 1.157 Stage 2 Hodgkin lymphoma** in a 16-year-old girl.

**Fig. 1.158 Epstein-Barr virus** in a 16-year-old boy.

**Table 1.57 Unilateral hilar enlargement due to arterial enlargement**
Diagnosis	Findings	Comments
Poststenotic dilatation Fig. 1.159, p. 90	Enlarged main pulmonary segment and apparent enlargement of proximal left pulmonary artery. Proximal right pulmonary artery dilatation concealed on frontal radiograph.
Pulmonary hypertension with absent contralateral pulmonary artery	Small, oligemic contralateral lung.	For example, in unilateral pulmonary hypoplasia.

**Fig. 1.159 Poststenotic dilatation.** Chest radiograph in a 10-month-old girl with known severe pulmonary valvular stenosis. There is enlargement of the left hilum due to poststenotic dilatation of the main and left pulmonary arteries (arrows).

Simulated Hilar Enlargement

Apparent hilar enlargement, and particularly an increase in hilar density without enlargement, may be due to superimposed densities on the frontal projection. This is usually clarified by a lateral projection or CT examination.

**Table 1.58 Pitfalls with unilateral hilar enlargement or density**
Diagnosis	Findings	Comments
Segmental pneumonia in the superior segments of the lower lobes	Frontal view: projects over the hilar region. Lateral view: posterior in position. Hilum unremarkable.	Signs of pneumonia.
Atelectasis of the RUL, one of the segments, or partial atelectasis of the middle lobe	Diagnosis on the lateral view, hilum unremarkable	Clinical symptoms (e.g., dyspnea).
Metastases Fig. 1.160a, b	Round densities that project outside of the hilum on the lateral radiograph.
Mass posterior to hilum		For example, metastasis, intrapulmonary bronchogenic cyst.