A 5-month-old full-term boy is brought to the physician for fever. He was doing well until this morning, when he felt warm to his mother. He has had a "runny nose" and intermittent coughing but otherwise has been breastfeeding well. His 3-year-old brother had an upper respiratory tract infection last week. The infant takes vitamin D, and his vaccinations are up to date. His temperature is 38. 9 C (102 F), blood pressure is 90/60 mm Hg, pulse is 120/min, and respirations are 32/min. Pulse oximetry shows an oxygen saturation of 96%. Examination shows crusted rhinorrhea at the nares. The patient's chest radiograph is shown below. Which of the following is marked on this patient's chest radiograph?

Question

A 5-month-old full-term boy is brought to the physician for fever.  He was doing well until this morning, when he felt warm to his mother.  He has had a "runny nose" and intermittent coughing but otherwise has been breastfeeding well.  His 3-year-old brother had an upper respiratory tract infection last week.  The infant takes vitamin D, and his vaccinations are up to date.  His temperature is 38. 9 C (102 F), blood pressure is 90/60 mm Hg, pulse is 120/min, and respirations are 32/min.  Pulse oximetry shows an oxygen saturation of 96%.  Examination shows crusted rhinorrhea at the nares.  The patient's chest radiograph is shown below.  Which of the following is marked on this patient's chest radiograph?

Quizplus · Accepted Answer

11ec25c8_d71c_d2fd_bc81_83fa051e7a16_MD0003_00 The thymus is normally visible on chest x-rays in children age <3 years. It is located in the anterior mediastinum behind the sternum and in front of the heart, aortic arch, and trachea. It appears prominent on infant x-rays due to its relatively large size compared to the infant's small thorax. On frontal views, the thymus is most commonly recognized as the "sail sign" (Image) due to its triangular shape, scalloped border, and uniform density. However, the shape is actually quite variable with phases of respiration as it is a soft gland. It also can shrink during times of stress or illness and rebound to a larger size after recovery (rebound hyperplasia). The thymus is an important organ in utero and during infancy and childhood for lymphocyte production and maturation. Its absence on neonatal x-ray could be suggestive of thymic hypoplasia or aplasia (eg, DiGeorge syndrome). The thymus normally atrophies and is replaced by fat after puberty, when it has completed production of T-lymphocytes. Therefore, adults with mediastinal opacities on x-ray should undergo further workup for pathology. Residual thymic tissue can undergo malignant transformation into a thymoma, which can occur in patients with myasthenia gravis. Lymphoma should also be on the differential for an anterior mediastinal mass in children and adults. thymic hypoplasia or aplasia Due to its location, the thymus can be misdiagnosed as a variety of pathological findings. (Choice A) Hilar lymphadenopathy is never normal and raises concern for malignancy (eg, lymphoma, metastases), infection (eg, tuberculosis, histoplasmosis), or inflammation (eg, sarcoidosis). This infant has no symptoms or x-ray findings suggestive of an abnormal mediastinal mass. Hilar lymphadenopathy (Choice B) Right atrial enlargement can give the appearance of cardiomegaly. Infants age <1 year normally have a transverse cardiothoracic ratio of <60%. Children age >1 year and adults should have a cardiothoracic ratio of <50%. This infant has a normal cardiac silhouette. Right atrial enlargement < > < (Choices C and E) Right middle or upper-lobe infiltrates are typical locations for aspiration pneumonia in infants or other patients who are primarily in the supine position. Infants with aspiration from swallowing dysfunction typically experience choking or gagging preceding respiratory distress. This infant has no infiltrates on x-ray. Right middle (Choice D) Right upper-lobe atelectasis appears as a linear density with associated shifting of the mediastinum toward the collapsed lung. Right upper-lobe atelectasis Educational objective: A large thymic silhouette is a normal finding on frontal chest x-ray in children age <3 years due to its relatively large size compared to the young child's thorax. Opacities in this location in other children should raise concern for pneumonia or malignancy, depending on the clinical context. References: Clinical and radiologic review of the normal and abnormal thymus: pearls and pitfalls. (http://www.ncbi.nlm.nih.gov/pubmed/20228326)

A 5-Month-Old Full-Term Boy Is Brought to the Physician for Fever