Cystic Airspaces Research Articles

Honeycombing on CT; its definition, pathologic correlation, and future direction of its diagnosis

Honeycombing on CT is the clue for the diagnosis of usual interstitial pneumonia (UIP) and its hallmark. According to the ATS-ERS-JRS-ALAT 2010 guideline, the patients with honeycombing on CT can be diagnosed as UIP without surgical biopsy. On CT scans, it is defined as clustered cystic airspaces, typically of comparable diameters of the order of 3–10mm, which are usually subpleural and have well-defined walls. Pathologically, honeycombing consists of both collapsing of multiple fibrotic alveoli and dilation of alveolar duct and lumen Although the definition of honeycombing seems to be strict, recognition of honeycombing on CT is various among each observer Because typical honeycombing is frequently observed in the patients with UIP, we should judge clustered cysts as honeycombing when a diagnosis of UIP is suspected.

Lung Cancer Associated With Cystic Airspaces

The objectives of this study were to determine the frequency of lung cancers associated with a discrete cystic airspace and to characterize the morphologic and pathologic features of the cancer and the cystic airspace. We reviewed all diagnosed cases of lung cancer resulting from baseline screening (n=595) and annual screening (n=111) in the International Early Lung Cancer Action Program to identify those abutting or in the wall of a cystic airspace. We also reviewed the pathologic specimens. A total of 26 lung cancers were identified abutting or in the wall of a cystic airspace. Of these, 13 were identified at baseline (13/595, 2%) and 13 at annual screening (13/111, 12%), which was significant (p<0.0001). The median circumferential portion of wall involved was less for the annual cancers than for the baseline ones, but this difference did not reach significance (90° vs 240°, p=0.07). The diagnosis was adenocarcinoma in all but three cases. Histologic analysis showed that the cystic space was a bulla, a fibrous walled cyst without a defined lining, or a pleural bleb and that in all but one case, the tumor was eccentric relative to the airspace and the wall of the airspace was unevenly thickened. At annual repeat CT screening, the finding of an isolated cystic airspace with increased wall thickness should raise the suspicion of lung cancer.

Diffuse Cystic Lung Disease of Unexplained Cause With Coexistent Small Airway Disease

Diffuse "true" cystic lung disease is rare, and the specificity of high-resolution computed tomography (HRCT) has reduced the need for biopsy. We present 5 patients with similar clinical and HRCT features of cystic lung disease that were sufficiently atypical to warrant surgical lung biopsies that showed coexistent small airway diseases (SAD). There were 4 female patients and 1 male patient with a mean age of 43 years. All were never smokers. Four had symptoms such as dyspnea (1), cough (2), or both (1). HRCTs showed variably sized thin-walled cystic airspaces without zonal distribution, some with prominent vessels in their walls. One case was unilateral. Surgical lung biopsy showed cystic change comprising localized loss of alveolar density with coexistent SADs [chronic bronchiolitis (n=2), eosinophilic bronchiolitis, probable asthma (n=1), and diffuse idiopathic neuroendocrine cell hyperplasia (n=2)]. Two patients who were tested for Birt-Hogg-Dube-related gene mutations proved negative, and all lacked other features of Birt-Hogg-Dube. We hypothesize that chronic damage to small airways may lead to cystic degeneration in a minority of patients. Precedents in relation to Sjogren syndrome and hypersensitivity pneumonitis raise the possibility of a causal association between pathologies in these 2 anatomic compartments, although HRCT data in relation to common SADs indicate that this would be a rare phenomenon. The driving factor remains unknown.

A Case of Multisystemic Langerhans Cell Histiocytosis in an Adult

A 23-year-old female smoker presented in late 2008 with a large left pneumothorax. She had multiple spontaneous pneumothoraces in 2007 which required pleurectomy. A presumptive diagnosis of lymphangioleiomyomatosis (LAM) was made in 2007 after the high-resolution computed tomography (HRCT) of the thorax revealed bilateral interlobular septal thickening and multiple thin walled cystic air spaces without lobar predilection, and with preservation of lung volumes.

A clinicopathological analysis of pulmonary lymphangioleiomyomatosis

背景与目的肺淋巴管平滑肌瘤病（pulmonary lymphangioleiomyomatosis, PLAM）是一种罕见的具有独特临床病理特征的肿瘤性疾病，本文旨在探讨PLAM的临床病理学特点及其鉴别诊断。方法收集3例PLAM病例，复习患者的临床资料，进行组织学及免疫组化观察，并结合文献复习分析。结果3例PLAM病例均为育龄妇女，年龄27岁-45岁，平均年龄37.7岁，其中2例胸部CT示双肺弥漫分布薄壁的含气囊腔，1例为气胸。组织学检测显示肿瘤组织呈不规则腔隙和斑片或结节状，由内皮细胞及其周围大量增生的平滑肌样梭形细胞构成，可沿支气管、血管等分布。免疫组织化学检测示增生平滑肌样梭形细胞呈现结蛋白（Desmin, Des）、钙结合蛋白（Caldesmon, Caldes）、平滑肌肌动蛋白（α-Smooth muscle actin, SMA）、肌特异性肌动蛋白（Muscle-specifc actin, MSA）、人类黑色素瘤单克隆抗体（HMB-45）、黑色素瘤标记物（Melanoma Marker, CD63）、波形蛋白（Vimentin, Vim）、雌激素（Estrogen, ER）和孕激素（Progestogen, PR）阳性表达，而T细胞1识别的黑色素抗原（Melanoma Antigen Recongnized by T cell 1, MRT-1）为阴性表达，毛细血管内皮细胞第8因子（FVⅢ）、人类造血干细胞表面分子（CD34）阳性表达，淋巴管内皮细胞呈淋巴管内皮细胞标记物（D2-40）阳性表达。本组病例随访时间为3个月-25个月，生存状况良好，未见该病复发，除肺外其余各系统未见淋巴管平滑肌瘤病等。结论PLAM的主要病理改变为沿支气管、血管分布的淋巴管周围平滑肌细胞异常增生，一般发病于绝经期前育龄女性，渐进性呼吸衰竭导致该病预后不良。

Characteristic crescentic subpleural lung zones with high ventilation (V)/perfusion (Q) ratios in interstitial pneumonia on V/Q quotient SPECT

Nonspecific interstitial pneumonia (NSIP) and usual IP (UIP) preferentially involve subpleural lung zones (SPLZ), and may result in characteristic regional lung function impairment. The aim of this study was to characterize cross-sectional lung ventilation (V)-perfusion (Q) imbalance in these disorders on automated V/Q quotient single photon emission computed tomography (SPECT). 99mTc-technegas/macroaggregated albumin SPECT-derived V/Q quotient SPECT and V/Q profile were automatically built for assessment of cross-sectional lung V-Q imbalance in 38 patients with NSIP or UIP. The findings of V/Q quotient SPECT were correlated with lung CT morphology. The results were compared with 12 healthy nonsmoker controls and 48 patients with chronic obstructive pulmonary disease. V/Q quotient SPECT showed 81 crescentic SPLZ with high V/Q ratios in 32 patients (84%) with NSIP or UIP, which were not observed in controls and patients with chronic obstructive pulmonary disease. Sixty-three (77.7%) of them were located at high-attenuation areas (reticular and/or ground-glass opacities) with or without small cystic air spaces (honeycombing and/or traction bronchiectasis) on CT, and 12 (14.8%) at normal lung areas. V/Q profile at the lung sections with crescentic SPLZ with high V/Q ratios showed flattened peaks with broadened V/Q ratio distribution compared with controls, and standard deviation of V/Q ratios in the entire lungs was significantly correlated with partial oxygen arterial blood pressure (P = 0.0009) and predicted diffusing capacity of the lungs for carbon monoxide (P = 0.0139). Five of eight patients with NSIP or UIP and with worsening of hypoxemia showed an extension of SPCZ with high V/Q ratios on follow-up V/Q quotient SPECT, without significant changes on CT. A high prevalence of crescentic SPLZ with high V/Q ratios is a characteristic feature of lung V-Q imbalance causing alveolar gas exchange impairment in NSIP and UIP.

Lung Morphology in the Elderly: Comparative CT Study of Subjects over 75 Years Old versus Those under 55 Years Old

To describe thin-section pulmonary computed tomographic (CT) features in asymptomatic elderly individuals. Institutional review board approval was given, and informed consent was obtained. Two study groups (older group, over 75 years of age; younger group, under 55 years) were prospectively identified from outpatient requests for CT of the abdomen or brain. Fifty-six consecutive volunteers (older group: n = 40, 18 men, 22 women; younger group: n = 16, eight men, eight women) with no known respiratory disease were included. Prone thin-section CT imaging was performed, and two observers independently scored images for the presence and extent of CT features (including reticular pattern, ground glass opacity, and thin-walled cystic air spaces). Group comparisons were made, and logistic regression analysis was used to assess relationships between CT findings and age and smoking history. A limited predominantly subpleural basal reticular pattern was identified in the majority (24 of 40, 60%) of individuals in the older group and was absent (zero of 16) in the younger group (P < .001). Cysts were seen in 10 (25%) of the 40 subjects in the older group but were seen in none of the subjects in the younger group (P = .02). Bronchial dilation and wall thickening were also seen significantly more frequently (P < .001) in the older group (24 [60%] and 22 [55%] of 40, respectively) than in the younger group (both one [6%] of 16). All findings were independent of pack-year smoking history with multiple logistic regression analysis. Thin-section CT findings usually associated with interstitial lung disease are frequently seen in asymptomatic elderly individuals and are absent in younger subjects. Therefore, these findings may not necessarily represent clinically relevant disease.

Metastasizing dermatofibroma in lung

Benign dermatofibroma is very common skin tumor and can very rarely metastasize. We report a case of metastasizing dermatofibroma on a 36-year-old woman who presented multiple bilateral lung nodules. She underwent incisional biopsy for cellular dermatofibroma of the right shoulder 7 years ago. Chest computed tomographic scanning shows multiple nodules in both lung fields. Segmental and wedge resections were done. Grossly, the masses were hemorrhagic cysts. Microscopically, there were dilated cystic airspaces. The airspaces were lined by respiratory and metaplastic squamous epithelium with underlying layers of fibrohistiocytic spindle cells with storiform and fascicular pattern. The tumor cells stained for CD68 and CD10. The lung mass shows same histologic features with skin lesion.

CT appearances of emphysema and clinical application

目的 研究不同类型肺气肿的CT表现及临床应用.方法 将33例尸检标本从气管灌注10%福尔马林,使肺膨胀至正常状态,1周后经气管注入氧气,直至液体全部从胸膜表面逸出,制成固定的充气标本,类似正常状态下肺组织,再将标本行冠状面及横轴面扫描.选取标本内有肺气肿的23例,分析其内肺气肿的表现及分布,然后将标本切成10 mm厚层,进行CT、病理对照.对15例经病理或临床综合诊断证实的病例行螺旋CT扫描,包括肺气肿合并感染11例,合并孤立性结节4例,分析肺气肿合并症的CT特征.结果 (1)23例肺气肿的标本中,小叶中心型肺气肿21例,全小叶型肺气肿5例,均与小叶中心型并发,间隔旁型肺气肿19例,瘢痕旁型肺气肿3例.(2)肺气肿均累及双侧肺野,呈大致对称或相近分布,17例(17/23)表现为2种或2种以上类型肺气肿并发.(3)肺气肿合并感染的14例(临床病例11例,标本3例)中,均见假空洞或假蜂窝影(实变肺野内未被充填的气肿腔);肺气肿合并结节者4例,见假胸膜凹陷征(间隔旁气肿或肺大泡的壁与结节相连).结论 肺气肿的CT表现、分布及多种类型合并存在等特点对空腔性病变的鉴别有帮助.提出肺气肿合并症的CT特征,假空洞影、假蜂窝影、假胸膜凹陷征及其对临床诊断与鉴别诊断的作用。

Lack of Evidence for an Association Between Neurofibromatosis and Pulmonary Fibrosis

To reassess the association between neurofibromatosis and pulmonary fibrosis. Retrospective single-center study with analysis of patients' chest radiographs, CT scans, and medical records. Tertiary care, referral medical center. One hundred fifty-six adult patients with neurofibromatosis seen over a 6-year period between 1997 and 2002. A review of chest radiographs revealed abnormal findings in 70 patients (44.9%). The most common radiographic abnormalities were extrapulmonary nodules or masses seen in 22 patients (14.1%), followed by skeletal abnormalities in 16 patients (10.3%). Bilateral interstitial infiltrates were noted in only three patients (1.9%), all of whom had potential causes other than neurofibromatosis for their lung infiltrates, including smoking-related interstitial lung disease, rheumatoid lung disease, recurrent pneumonias, and a history of ARDS. CT scans were available in two of these patients and revealed nonspecific patterns of abnormalities with no honeycombing. Six patients had bullae or cystic airspaces demonstrated on chest radiography or CT scan; all of these findings occurred in the context of smoking-related emphysema. Combined together, bilateral interstitial lung infiltrates or cystic airspaces were demonstrated in five patients (3.2%) by chest radiography, and in eight patients (5.1%) by chest radiography or CT scanning; one patient had both findings on the CT scan. We found little evidence to support an association between neurofibromatosis and pulmonary fibrosis or any other form of parenchymal lung disease. Interstitial lung disease and bullae described in association with neurofibromatosis in previous reports may have, in part, represented smoking-induced manifestations.

Cystic fibrohistiocytic tumours presenting in the lung: primary or metastatic disease?

Cystic fibrohistiocytic tumour of the lung is a rare proliferative process. Its histogenesis is uncertain, but evidence suggests that some cases represent metastatic disease from apparently indolent skin lesions, namely cellular fibrous histiocytomas. This study presents four cases and reviews the literature concerning this pattern of disease and its aetiology. All patients were male (age range 35-54 years). Two presented with recurrent haemoptysis. Two cases had histories of cutaneous fibrohistiocytic lesions in the chest wall, excised 10 and 23 years prior to presentation with lung disease. Imaging data showed multiple bilateral cystic lung lesions in all four patients with nodular cavitating opacities seen on high-resolution computed tomography scans. Microscopy showed variably dilated thin-walled cystic airspaces lined by cuboidal epithelium and an underlying layer of mildly pleomorphic spindle cells with slightly wavy morphology and storiform architecture, admixed with inflammatory cells. Tumour cells stained for CD68 in three of four cases. All cases were negative for CD34. All patients were alive with disease, although one required pneumonectomy for intractable haemoptysis. This study and a review of published cases show that the majority of cystic fibrohistiocytic tumours of the lung probably represent metastases from cellular fibrous histiocytomas. However, rare cases may be either primary in origin or the primary site remains occult; the term cystic fibrohistiocytic tumour remains appropriate for such cases.

Lung cancer associated with diffuse pulmonary fibrosis: CT-pathologic correlation.

The authors reviewed the computed tomographic (CT) scans and pathologic specimens of 57 histologically proved bronchogenic carcinomas (35 squamous cell carcinomas, 12 small cell carcinomas, and 10 adenocarcinomas) in 47 patients with diffuse pulmonary fibrosis. The patients ranged in age from 61 to 87 years (mean age, 72 years; 42 men and 5 women). On radiography and CT, most tumors (82%) were located in peripheral areas of honeycomb lung. In 50 of the 57 lesions, the tumors were round or lobulated with sharp margins. In seven tumors, including six squamous cell carcinomas and one small cell carcinoma, the tumor invaded the adjacent honeycomb lung and lacked distinct margins. Intratumor lucency was seen in 13 tumors (five solitary and eight multiple). The CT findings, including high-resolution CT scans, were compared with the histologic findings in a subgroup of 29 lesions in 25 patients with available surgical or autopsy specimens. Invasive growth of tumors with unclear margins (four lesions), septal thickening of the contiguous/surrounding honeycombed areas (16 lesions), and discrete masses (nine lesions) with solitary (four of nine) or multiple (five of nine) intratumor lucencies. The lucencies in six of nine patients (67%) with intratumor lucencies were found to represent engulfed cystic airspaces histologically. CT revealed that bronchogenic carcinoma associated with diffuse pulmonary fibrosis has distinct morphologic characteristics that correlate histologically with a specific pattern of tumor growth.

Lymphangioleiomyomatosis. A series of three case reports illustrating the link with high oestrogen states.

Lymphangioleiornyomatosis is a rare lung disorder characterised by cystic air spaces and smooth muscle proliferation. The condition, which most commonly presents with dyspnoea, pneumothoraces or cough, is only described in females and is most commonly diagnosed during childbearing years. Three cases are presented which illustrate typical features of the disease and the association with high oestrogen levels. The first had recurrent pneumothoraces during her first pregnancy. The second lady was post menopausal at diagnosis but her symptoms predated her menopause. The third, presented with dyspnoea, abnormal chest sensations and a pneumothorax. She had a history of hyperprolactinaemia with secondary amenorhoea due to low oestrogen levels which had been corrected prior to her presentation. All three patients had reduced gas transfer and abnormalities in spirometry, two had reticular shadowing on their chest radiograph and all had typical appearances on lung computerised tomography. Although disease progression was variable, all patients showed a gradual decline in lung function.

Lymphocytic interstitial pneumonia: follow-up CT findings in 14 patients.

The aim of the present study was to assess the evolution of various computed tomographic (CT) findings of lymphocytic interstitial pneumonia (LIP) with determination of potentially reversible or irreversible features. The study included 14 patients with biopsy-proved LIP who had serial thin-section CT examination 4 to 82 months (median 13 months) apart. Initial and follow-up CT scans were evaluated independently and then directly compared with each other by two observers. The main parenchymal abnormalities on the initial CT scan consisted of ground-glass attenuation (n = 14), thickening of interlobular septa (n = 13), centrilobular nodules (n = 12), cystic airspaces (n = 10), and airspace consolidation (n = 4). On follow-up CT, nine patients improved, one showed no change, and four showed increased extent of disease. With the exception of cysts, the parenchymal opacities were reversible. On follow-up CT, new cysts were seen in three patients; these developed mainly in areas with centrilobular nodules on initial CT. Honeycombing was seen on follow-up CT in four patients; in three patients it developed in areas of airspace consolidation and in one patient it developed in an area with ground-glass attenuation on initial CT. The majority of patients with LIP improved on follow-up. However, airspace consolidation may progress to honeycombing and centrilobular nodules may precede cystic formation.

Lymphocytic interstitial pneumonia: thin-section CT findings in 22 patients.

To assess the thin-section computed tomographic (CT) findings of lymphocytic interstitial pneumonia. The study included 22 patients (five men, 17 women; age range, 24-83 years; mean age, 50 years) with biopsy-proved lymphocytic interstitial pneumonia. The CT scans were obtained by using 1-3-mm collimation and reconstructed by using a high-spatial-frequency algorithm. The predominant abnormalities consisted of areas of ground-glass attenuation and poorly defined centrilobular nodules present in all 22 patients and subpleural small nodules seen in 19 patients. Other common findings included thickening of bronchovascular bundles (n - 19), interlobular septal thickening (n = 18), cystic airspaces (n = 15), and lymph node enlargement (n = 15). Less common findings included large nodules, emphysema, airspace consolidation, bronchiectasis, architectural distortion, honeycombing, and pleural thickening. Lymphocytic interstitial pneumonia is characterized by the presence of ground-glass attenuation, poorly defined centrilobular nodules, and thickening of the interstitium along the lymphatic vessels. Lymph node enlargement is more common than previously recognized; it was seen in 68% of patients.

Technical report: Cystic air spaces in the lung: Change in size on expiratory high-resolution CT in 23 patients

To determine the presence of change in size of air-filled cysts in the lung on expiration by comparison between inspiratory and expiratory high-resolution computed tomography (CT) scans. Inspiratory and expiratory high-resolution (1-mm collimation) CT scans were obtained in 23 patients with lung cysts due to a variety of lung diseases. The 23 patients had a total of 27 types of cystic lesions including bullae (n=7), honeycomb cysts due to fibrosing alveolitis (n=11), lymphangioleiomyomatosis (LAM, n=2), cystic adenomatoid malformation (n=1), and bronchiectasis (n=6). An adequate expiratory effort, with at least 5% decrease in the anteroposterior or transverse thoracic diameter, was required for inclusion in the study. Inspiratory and expiratory scans at corresponding anatomic levels were compared to determine any change in size of the cysts on expiration. Cystic lesions due to bronchiectasis, LAM and fibrosing alveolitis decreased in size on expiratory CT. In six of seven cases bullae decreased in size, and in one patient with a single bulla it remained unchanged. In one case a single cyst due to cystic adenomatoid malformation increased in size on expiration. The majority of lung cysts decrease in size on expiration suggesting that they communicate with the airways.

Regional ventilation-perfusion mismatch in interstitial pneumonia. Correlation between scintigraphy and CT.

Interstitial pneumonia is one of the many causes of a scintigraphic ventilation-perfusion (V/Q) mismatch. To evaluate the morphologic features of V/Q mismatched areas in patients with interstitial pneumonia, we correlated the findings on lung scintigraphy using Kr-81m and Tc-99m MAA with CT scan findings. Of 41 patients, 20 (49%) had a high V/Q mismatched areas. All of these areas corresponded to cystic air spaces shown on CT, and most of the showed a honeycomb pattern. Ventilation-perfusion matched defects were seen in 23 patients (56%). The matched defects corresponded to cystic air spaces (honeycomb or bullous changes) or lung attenuation changes of varying degrees on CT. Cystic air spaces with high V/Q mismatch are considered to be normally ventilated. To distinguish mismatched areas of interstitial pneumonia from areas of pulmonary embolism, it may be necessary to compare scintigraphic findings with CT.

Bronchioloalveolar carcinoma: computed tomography findings

The aim of the present study was to investigate the appearance of bronchioloalveolar lung carcinoma on computed tomography (CT) scans, and to determine the frequency of signs suggestive of this diagnosis. CT features of 42 cases with pathologically proven bronchioloalveolar carcinoma were retrospectively analysed for pattern, size, location and secondary signs suggesting the diagnosis. Bronchioloalveolar carcinoma had one of the following patterns: solitary nodule or mass (16), lobar consolidation (10), multilobar consolidations (13) and diffuse nodules (3). The 16 solitary nodules or masses ranged in size from 2.0 to 9.4 cm (mean +/- SD 3.75 +/- 1.7 cm). Eleven of the 16 nodules or masses were peripheral and five were central: Eight of the 16 tumours had pleural tags, seven had spiculated margins, and three had bubblelike lucencies. The consolidations were peripherally distributed in 13 out of 23 cases; cystic airspaces were observed in 19 out of 23 consolidations; bulging of interlobar fissures in 8 out of 23; and the angiogram sign in 7 out of 23. In conclusion, computed tomography findings of bronchioloalveolar carcinoma have a wide spectrum, showing typically a peripheral nodule or consolidation. Computed tomography has a role in the diagnosis of nodular localized versus other forms, with subsequent therapeutic and prognostic implications.

Pedunculated pulmonary leiomyoma with large cyst formation

A case of single pulmonary leiomyoma with giant cyst formation is presented. Metastasizing uterine fibroleiomyoma and fibroleiomyomatous hamartoma both give rise to multiple pulmonary nodules on chest films. Leiomyoma of the lung presenting as a single pedunculated lesion with cyst formation is exceptional. This report documents the existence of other rate cystic lesions that may mimic the more common cystic air space and bullous disease.

Cause of regional ventilation-perfusion mismatching in patients with idiopathic pulmonary fibrosis: a combined CT and scintigraphic study.

Regional ventilation and perfusion were studied in patients with idiopathic pulmonary fibrosis (cryptogenic fibrosing alveolitis) to seek an explanation for the mismatched ventilation/perfusion (V/Q) seen on scintigrams, which may suggest pulmonary embolic disease. Eight patients with idiopathic pulmonary fibrosis were examined with inspiratory and expiratory CT scans. Planar and tomographic (single-photon emission computed tomography, SPECT) scintigraphy, using inhalation of krypton-81m gas (ventilation) and IV injection of 99mTc-albumin macroaggregates (perfusion), also was performed. The lungs were divided into quadrants (cranial, caudal, right, left) for analysis. Cystic air spaces with a "honeycomb" appearance occupied more than 33% of the cross-sectional area in 75% of all lung quadrants (n = 16), more than 66% of the area in 44% of quadrants, and less than 33% of the area in the remaining 25% of quadrants. On expiratory CT scans, the cross-sectional area of the cystic spaces diminished significantly (unlike emphysematous spaces). Sixty-seven percent of lung quadrants, corresponding to those with marked or moderate involvement with cystic spaces, showed a mismatched V/Q pattern on scintigrams (absent perfusion, normal ventilation); 27% of quadrants had matched V/Q defects, and 6% did not show defects. Two patients had, in addition, large cystic spaces typical of emphysema, but the coexistent fibrosis prevented the gross air trapping seen in bullous emphysema. The cystic air spaces that are often seen on CT scans of patients with idiopathic pulmonary fibrosis are unperfused (probably due to vascular obliteration) but are usually normally ventilated. This V/Q mismatch on scintigrams explains the large physiologic dead space seen at rest and on exercise and could suggest pulmonary embolism unless a CT scan is obtained. Conversely, the larger cystic spaces might be mistaken for emphysema unless V/Q scintigraphy is done.