January 2010, VOLUME 194
NUMBER 1

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January 2010, Volume 194, Number 1

Residents' Section

Pattern of the Month

Multiple Cystlike Lung Lesions in the Adult

+ Affiliation:
1All authors: Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave., Boston, MA 02215.

Citation: American Journal of Roentgenology. 2010;194: W1-W11. 10.2214/AJR.09.3540

Keywords: cysts, lung, pattern

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Multiple lung cysts in the adult population can be encountered in a wide variety of conditions. A cyst is defined as a round circumscribed space that is surrounded by an epithelial or fibrous wall of variable thickness. A cyst usually has a thin and regular wall (< 2 mm) and contains air, although some may contain fluid. The thin wall of cystic lesions differentiates them from cavitary processes, which have thicker and irregular walls and will not be discussed in this article. On chest radiographs, findings of a cyst are often subtle, consisting of lucencies and sometimes linear opacities. An air–fluid level can improve the visibility of a cyst and may suggest infection. For the investigation of cysts, CT is substantially more sensitive than chest radiography, showing a cyst as a ringlike lucency surrounded by a thin wall (Fig. 1A, 1B).

Table 1 summarizes the most common causes of multiple lung cysts. Pitfalls in the detection of lung cysts on CT include cystic bronchiectasis and emphysema accompanied by bullae.

TABLE 1: Causes of Multiple Cystlike Lung Lesions in Adults

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Fig. 1A Multiple cysts. Multiple infected lung cysts with air–fluid levels (arrows) on chest radiograph.

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Fig. 1B Multiple cysts. In another patient, multiple ringlike lucencies (arrows) in lymphangioleiomyomatosis.

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Fig. 2 Multiple upper lobe predominant bullae (arrow) in emphysematous patient.

Blebs and Bullae
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Blebs and bullae are sharply defined, air-containing spaces that are bounded by curvilinear, hairline shadows. According to the Fleischner Society Glossary of Terms for Thoracic Imaging, a bleb is a cystic space l cm or less in diameter; anything larger than this is defined as a bulla. Bullae can reach substantial size and occupy an entire lobe. Blebs and bullae are commonly subpleural and are mostly seen in both upper lobes in patients with coexisting centrilobular and paraseptal emphysema (Fig. 2). In severe cases, or in patients with recurrent pneumothoraces, bullectomy can improve pulmonary function or even be curative.

Congenital Pulmonary Airway Malformation
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Congenital pulmonary airway malformation, formerly known as congenital cystic adenomatoid malformation, is a rare multicystic, intralobar mass of disorganized lung tissue, most often seen in the lower lobes. It is usually diagnosed in children but can be left unrecognized until adulthood. Congenital pulmonary airway malformation can be categorized into three subtypes on the basis of its appearance. Type 1 is most frequent, especially in the adult population, and consists of multiple cysts 2 cm or greater in diameter. On CT, the disease appears as a large, air-filled multicystic lesion (Fig. 3A, 3B, 3C). Type 2 is defined as multiple cysts smaller than 2 cm. In type 3, the least frequent type, there are numerous microscopic cysts that often have a more solid appearance on imaging. Type 3 has the worst prognosis, which presumably is the reason it is uncommon in adults. Complications of congenital pulmonary airway malformation include infection and malignant transformation. Therefore, surgical resection is recommended for definitive treatment.

Honeycombing
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Honeycombing is one of the manifestations of fibrotic lung disease. The most common cause of honeycombing is usual interstitial pneumonia (UIP), but this appearance can also be seen in conditions such as nonspecific interstitial pneumonia, sarcoidosis, chronic hypersensitivity pneumonitis, asbestosis, and postradiation fibrosis.

On CT, honeycombing consists of multiple cysts of variable thickness and size, with more than one layer of cysts, usually distributed bilaterally and mostly in the subpleural and basilar regions (Fig. 4). It is usually accompanied by other signs of fibrosis, such as traction bronchiectasis or bronchiolectasis, reticulation, and ground-glass opacities.

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Fig. 3A Congenital pulmonary airway malformation type 1 in adulthood. Chest radiograph (A) and coronal (B) and transverse (C) CT reformations show right lower lobe multicystic lesion (long arrows). Double short arrows in C point to fluid-filled cyst.

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Fig. 3B Congenital pulmonary airway malformation type 1 in adulthood. Chest radiograph (A) and coronal (B) and transverse (C) CT reformations show right lower lobe multicystic lesion (long arrows). Double short arrows in C point to fluid-filled cyst.

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Fig. 3C Congenital pulmonary airway malformation type 1 in adulthood. Chest radiograph (A) and coronal (B) and transverse (C) CT reformations show right lower lobe multicystic lesion (long arrows). Double short arrows in C point to fluid-filled cyst.

Langerhans Cell Histiocytosis
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Langerhans cell histiocytosis (LCH) is a destructive disorder that occurs almost exclusively in smokers and has no sex predominance. LCH is characterized pathologically by the formation of granulomas containing Langerhans cells; clinical findings include cough, dyspnea, and fatigue. Pneumothorax can also occur, either at the time of presentation or later during the course of the disease. As with other smoking-related diseases, such as emphysema, respiratory bronchiolitis, and desquamative interstitial pneumonia, LCH typically has upper lobe predominance with relative sparring of both bases. However, in some cases, LCH shows a more diffuse distribution with peribronchovascular predominance.

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Fig. 4 Honeycombing. Multiple predominantly subpleural and basilar cysts (arrows) in patient with usual interstitial pneumonia.

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Fig. 5A Langerhans cell histiocytosis. Transverse CT images show bizarre-shaped cysts (black arrows), cavitary nodules (white arrows), and noncavitary nodules (curved arrows) in upper lobe predominant distribution.

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Fig. 5B Langerhans cell histiocytosis. Transverse CT images show bizarre-shaped cysts (black arrows), cavitary nodules (white arrows), and noncavitary nodules (curved arrows) in upper lobe predominant distribution.

Radiographically, LCH appears as multiple nodules that range from 1 to 10 mm. The presence of cysts usually occurs only during the later stages of the disease. On CT, bizarre-shaped cysts are associated with noncavitary nodules that progressively cavitate to become thick-walled cavitary nodules and then thin-walled cysts (Fig. 5A, 5B). The CT findings of LCH are often characteristic and reflect the temporal heterogeneity of the disease. Treatment consists of smoking cessation, which can result in improvement of the abnormalities.

Lymphangioleiomyomatosis
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Lymphangioleiomyomatosis (LAM) is a disorder of smooth muscle proliferation that primarily affects women of childbearing age. However, it also can present after menopause in women undergoing estrogen hormonal treatment. This condition is indistinguishable from pulmonary involvement in tuberous sclerosis, which can also occur in men. Dyspnea and hemoptysis are common presenting symptoms. Chylothorax and pneumothorax are also frequently seen, either at presentation or during the course of the disease.

On chest radiographs, there are increased lung volumes and often a suspicion of linear or ringlike lucencies. CT shows well-defined, smooth, and regular cysts interspersed with normal intervening lung (Fig. 6A, 6B). In contrast to LCH, the distribution is diffuse and does not spare the costophrenic angles. Lung nodules are typically absent in LAM, whereas they are an essential part of the appearance in LCH. In the later stages of LAM, the cysts become larger and tend to become more numerous and coalescent. There may be associated lymphadenopathy and renal angiomyolipomas. Lung transplantation is the definitive treatment of this progressive disease, but recurrence can occur in the transplanted lung.

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Fig. 6A Lymph angio leiomyo matosis. Chest radiograph shows increased lung volumes and fine linear opacities.

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Fig. 6B Lymph angio leiomyo matosis. Transverse CT image shows multiple, well-defined, regular cysts interspersed with normal intervening lung.

Lymphocytic Interstitial Pneumonia
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Lymphocytic interstitial pneumonia (LIP) is typically associated with collagen–vascular diseases, especially Sjögren syndrome, and AIDS. Other less frequently reported disorders associated with LIP include autoimmune thyroid disease, Castleman disease, systemic lupus erythematosus, myasthenia gravis, pernicious anemia, and chronic active hepatitis. It is currently controversial whether LIP represents a benign lymphoproliferative disorder or a form of early lymphoma.

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Fig. 7A Lymphocytic interstitial pneumonia (LIP). Transverse (A) and coronal (B) CT reformations show scattered cysts (arrows) in patient with Sjögren syndrome and LIP.

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Fig. 7B Lymphocytic interstitial pneumonia (LIP). Transverse (A) and coronal (B) CT reformations show scattered cysts (arrows) in patient with Sjögren syndrome and LIP.

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Fig. 7C Lymphocytic interstitial pneumonia (LIP). In another patient with AIDS and LIP, transverse CT image shows numerous lung cysts (arrows).

LIP may produce a fine linear or reticulonodular pattern on chest radiographs. On CT, the lung cysts are usually less numerous than in LCH or LAM. During the acute phase, diffuse or multifocal ground-glass opacities are seen. However, these opacities may regress so that cysts are the only residual finding in more chronic cases (Fig. 7A, 7B, 7C). Less frequently, LIP presents with a reticular or reticulonodular pattern, lung nodules, or consolidation. Lymph node enlargement can also occur. The usual treatment is steroid therapy, after which ground-glass opacities can resolve. The cysts, however, persist even after therapy.

Metastases
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Thin-walled cystic metastases develop primarily in sarcoma, squamous cell cancer, transitional cell carcinoma of the bladder, and melanoma. Less frequently, this pattern may be seen with lymphoma. As with other metastatic lesions, cystic metastases tend to have different sizes and a basilar predominance (Fig. 8). A potential complication of cystic metastases is pneumothorax, which may require placement of a chest tube.

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Fig. 8 Multiple cystic colon metastases (arrows).

Neurofibromatosis Type 1
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Neurofibromatosis type 1, or von Recklinghausen disease, is clinically characterized by café-au-lait spots, neurofibromas, axillary or inguinal freckling, optic nerve glioma, Lisch nodules, and skeletal lesions. Rarely, it can be associated with multifocal lung cysts, which most commonly involve both upper lobes (Fig. 9A, 9B, 9C). Other chest manifestations include subcutaneous and intercostal neurofibromas, ribbonlike ribs, meningoceles, mediastinal masses, and pulmonary fibrosis.

Pneumatoceles
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Pneumatoceles are thin-walled, gas-filled spaces in the lung that are most frequently caused by pneumonia, trauma, or inhalation of hydrocarbon fluid. In the acute phase, pneumatoceles can be thick-walled. They tend to become thinner in the chronic phase. When due to infection, Pneumococcus species, Escherichia coli, Klebsiella species, and Staphylococcus species are the most common offending bacterial organisms, and pneumatoceles tend to appear in the healing phase. Among nonbacterial organisms, Pneumocystis jiroveci pneumonia has become an important cause of pneumatoceles in recent years (see next section). Infectious pneumatoceles are usually transient, and spontaneous resolution is generally the rule. The development of posttraumatic pneumatoceles is often preceded by lacerations and contusions of the lung, and healing occurs within weeks to months. On CT, pneumatoceles manifest as scattered thin-walled cysts interspersed with normal lung in areas previously affected by pneumonia or trauma (Fig. 9A, 9B, 9C).

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Fig. 9A Pneumatoceles. Transverse CT images show pneumatocele (arrows) before (A) and after (B) treatment in fire eater.

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Fig. 9B Pneumatoceles. Transverse CT images show pneumatocele (arrows) before (A) and after (B) treatment in fire eater.

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Fig. 9C Pneumatoceles. Multiple pneumatoceles (arrows) after recurrent infections in patient with AIDS.

Pneumocystis Jiroveci Pneumonia
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Pneumocystis jiroveci pneumonia (PJP), formerly known as Pneumocystis carinii pneumonia, was classified as a protozoan but is now known to be a fungal infection. It is almost exclusively seen in immunosuppressed patients, especially in those with AIDS who have a CD4 count below 200 cells/mm3. The symptoms can be insidious but may progress to respiratory failure and even death, often following a rapid, fulminant course if left untreated. Once a common opportunistic infection, PJP is now less frequently seen because patients with AIDS receive standard prophylaxis with trimethoprim sulfamethoxazole. The diagnosis can be made by sputum culture, bronchoscopy with lavage, or biopsy.

The radiographic manifestations of PJP vary widely, ranging from a totally normal chest radiograph to widespread, bilateral, symmetric opacities that are often of ground-glass density. The distribution often has perihilar and bibasilar predominance, but it can primarily affect the upper lobes in patients receiving prophylactic therapy for this infection. There may be a reticular pattern and even progression to consolidation. Pleural effusions are almost always absent, and their presence should raise the possibility of an alternate diagnosis. On CT, PJP often appears as a pattern of bilateral, multifocal, mainly symmetric ground-glass opacities (Fig. 10A, 10B). More focal areas of consolidation are also common. PJP-related cysts tend to occur mostly after multiple infections, can have an apical predominance, and may lead to pneumothoraces, which portend a poor outcome. Other less frequent manifestations include a reticular or reticulonodular pattern and pulmonary nodules.

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Fig. 10A Pneumocystis jiroveci pneumonia. Chest radiograph shows bilateral, symmetric, mostly perihilar and bibasilar ground-glass opacity.

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Fig. 10B Pneumocystis jiroveci pneumonia. Transverse CT image confirms bilateral, widespread ground-glass opacity and shows scattered lung cysts (arrow).

Tracheobronchial Papillomatosis
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The rare lung parenchymal involvement by tracheobronchial papillomatosis is usually accompanied by very slowly progressive papillomas of the larynx, trachea, and mainstem bronchi. The disease has a bimodal age distribution, occurring most often early in life or in the fourth decade. In adults, it is more prevalent in men. Clinically, tracheobronchial papillomatosis can manifest as hoarseness, dyspnea, and hemoptysis.

The radiographic findings are nonspecific and include cystic lucencies and nodules. On CT, papillomas of the airway can easily be visualized. The associated cysts are less numerous than in LAM or LCH and typically have a posterior predominance (Fig. 11A, 11B).

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Fig. 11A Tracheobronchial papillomatosis. Multiple, bilateral lung cysts on transverse (A) and coronal (B) CT reformations. Arrows point to larger cysts.

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Fig. 11B Tracheobronchial papillomatosis. Multiple, bilateral lung cysts on transverse (A) and coronal (B) CT reformations. Arrows point to larger cysts.

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Fig. 12 Emphysema. Transverse CT image shows upper lobe predominant lucencies (arrows) with no visible wall, caused by destruction of lung parenchyma.

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Fig. 13 Cystic bronchiectasis. Transverse CT image shows cystlike lesions (arrows) contiguous with dilated bronchi.

Pitfalls
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Emphysematous changes sometimes can be mistaken for multifocal lung cysts. In contrast to true cysts, the cystlike lucencies caused by the destruction of lung parenchyma in emphysema do not have walls (Fig. 12). Nevertheless, emphysema can be accompanied by multiple cysts, such as bullae, or in association with LCH.

Cystic bronchiectasis can also be mistaken for cysts at CT if thin-section images are not reviewed. Multiplanar reformations can be helpful to distinguish cystic bronchiectasis, in which there is continuity of a bronchus with thin-walled lucencies and true cysts, in which such communication does not exist (Fig. 13).

Address correspondence to R. L. Eisenberg ().

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Suggested Reading
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