Bronchial Atresia

Chest radiograph shows a well circumscribed tubular mass in the left upper lobe with distal localized emphysema in a 41-year-old asymptomatic patient.

Coronal-reformatted CT image demonstrate the mass to be a dilated segment of left upper lobe bronchus filled with mucus. Localized emphysema in the left upper lobe is confirmed.

Facts: Bronchial Atresia

• Absence of communication between a segment or subsegmental bronchus and the central airways.
• Most cases are found incidentally on imaging (asymptomatic)
• Most common location = apical posterior segment of the left upper lobe.

Imaging Features

• Mucus plug surrounded by hyperlucent lung.
• Absence of enhancement (enhanced CT and/or endoscopic examination may be required to exclude an endoluminal obstructing lesion)
• Absence of communication with pulmonary vessels

Differential Diagnosis

• Mucous plug distal to bronchial obstruction (endobronchial neoplasm, for example)
• Focal bronchiectasis with mucus plugging
• Pulmonary sequestration
• Allergic bronchopulmonary aspergillosis
• Vascular malformation

Reference:

Parker MS, Rosado de Christenson ML, Abbott GF. Teaching Atlas of Chest Imaging, 2005.

Hyperechoic Renal Mass

A longitudinal sonographic view of the right kidney shows a hyperechoic mass in the upper pole of the kidney (arrow) in this asymptomatic woman.

Differential Diagnosis: Hyperechoic Renal Mass

• Angiomyolipoma (AML)
• Renal cell carcinoma (RCC) (esp. papillary type)

Facts

• Most common cause of hyperechoic renal mass = AML
• 20% - 50% of small RCCs (less than 3 cm) are hyperechoic
• Hence, on the basis of echotexture along, ultrasound cannot reliably differentiate an AML from renal cell carcinoma
• US features suggestive of RCC: 1) anechoic rim, 2) cystic area within the mass (intratumoral cyst)
• CT or MRI is warranted to further evaluate a hyperechoic renal mass

Our case: subsequent CT shows fat within the mass, consistent with AML.

References:

1. Yamashita Y, Ueno S, Makita O, et al. Hyperechoic renal tumors: anechoic rim and intratumoral cysts in US differentiattion of renal cell carcinoma from angiomyolipoma. Radiology 1993; 188:179-182.

2. Vikram R, Ng CS, Tamboli P, et al. Papillary renal cell carcinoma: radiologic-pathologic correlation and spectrum of disease. RadioGraphics 2009; 29:741-754.

Centrilobular Nodules with Tree-in-Bud Pattern

Axial CT image shows multiple micronodules in the left lung. Most are not subpleural. They are non-uniform and there are some that have V- or Y shape.

Facts: Centrilobular Nodules

• Nodules limited to centrilobular structure (central core), sparing pleural surfaces
• Most peripheral nodules are centered 5-10 mm from fissures or pleural surface
• Evenly distribulted
• Common cause: without tree-in-bud - infection, inflammation, hypersensitivity, vascular disease
• Common cause: with tree-in-bud - infection

Random Nodules

Axial CT image shows multiple micronodules throughout both lungs. Some of the nodules are subpleural, and they are uniform in distribution.

Facts: Random Nodules

• Nodules are randomly, and evenly distributed relative to structures of the lung and lobule
• They tend to be symmetric
• Often involve pleural surfaces (with subpleural nodules)
• Common cause: hematogenous metastasis, miliary infection (TB, fungus)

Our case: hematogenous metastasis.

Perilymphatic Nodules

Axial CT image shows multiple micronodules and small nodules throughout both lungs. Note that there are subpleural nodules (best seen along the fissures), and they arrange in a non-uniform fashion.

Facts: Perilymphatic Nodules

• Located along pulmonary lymphatics (wall and central core structure of the secondary pulmonary lobule)
• Most notable along the fissures (subpleural region)
• Can be peribronchovascular in distribution
• Common causes: sarcoidosis and lymphangitic carcinomatosis
• Less common cause: silicosis, coal-worker pneumoconiosis

Our case: sarcoidosis

Imaging Approach to Pulmonary Micronodules and Small Nodules

Definition:

• Micronodule = nodules of less than 3 mm
• Small nodules = nodules of less than 2 cm

Steps for Decision Making

1. Decide whether there are multiple micronodules or small nodules
2. Where are the nodules? Are they subpleural?
3. If they are subpleural, are they uniformly distributed throughout the lungs or secondary pulmonary lobules?
4. If they are not subpleural, they are likely centrilobular. The next question is whether there is tree-in-bud pattern or not.
5. Look for associated findings as a clue to limit differential diagnoses

Osteochondroma: Imaging Features of Malignant Degeneration

A radiograph of the right shoulder shows a large pedunculated lytic mass (long arrows) in the proximal metadiaphysis of the humerus, with continuous cortex and marrow cavity. Note areas of disrupted cortex (short arrows).

Facts: Osteochondroma

• Benign bone tumor usually recognized on radiography as a lesion perpendicular to the parent bone, with a continuous cortex and marrow cavity.
• Pain from an osteochondroma is commonly caused by fracture, burisitis or compression of surrounding structures. Malignant degeneration of a single osteochondroma is rare.

Facts: Malignant Transformation of Osteochondroma

• 1% of solitary osteochondroma, 20% of hereditary form
• If transformed, most are to chondrosarcoma
• Average age of malignant transformation = 30 years

Imaging Features Suggesting Malignant Transformation

• Clinical: 30 years old, location at pelvis and shoulder, increasing pain and mass at site of known osteochondroma
• Imaging: thick/irregular calcified cap, bone destruction, soft tissue mass, altered appearance on sequential studies

Our case: pedunculated osteochondroma in a middle-aged patient presenting with increasing pain, suspicious for malignant transformation. Awaiting pathologic results.

References:

1. Yochum TR, Rowe LJ. Essentials of Skeletal Radiology, 3rd ed. 2005

2. Tehranzadeh J. Musculoskeletal Imaging Cases, 2009

Adrenal Myelolipoma

Axial CT image shows a large right adrenal mass (arrows) which contains several foci of macroscopic fat (arrowhead).

Facts:

• Benign biochemically inactive tumor of the adrenal gland thought to be due to metaplastic change of reticuloendothelial system of capillaries
• Contains mature adipose tissue and normal hematopoietic cells
• Most commonly occurs in adrenal glands, but can be seen in other tissues (ie, retroperitoneum presacral region)
• Most are asymptomatic (found incidentally on imaging). If large, or symptomatic, it can be treated with surgical excision and/or adrenalectomy
• Rare, less than 0.2% in population

Imaging Features

• Adrenal mass containing fat attenuation, virtually diagnostic of adrenal myelolipoma (bright on ultrasound, fat on CT and MR)
• May contain calcification

Reference:

Adrenal myeloliopma at URL: http://path.upmc.edu/cases/case165/dx.html