{{short description|Radiologic sign on radiographs and computed tomography scans}} {{use dmy dates|date=October 2020}} [[File:COVID-19-Longontsteking.jpg|thumb|High-resolution CT image showing ground-glass opacities in the periphery of both lungs in a patient with COVID-19 (red arrows). The adjacent normal lung tissue with lower attenuation appears as darker areas.]] '''[[Ground glass|Ground-glass]] opacity''' ('''GGO''') is a finding seen on [[Chest radiograph|chest x-ray]] (radiograph) or [[CT scan|computed tomography (CT)]] imaging of the [[lung]]s. It is typically defined as an area of hazy opacification (x-ray) or increased attenuation (CT) due to air displacement by fluid, airway collapse, [[fibrosis]], or a [[Neoplasm|neoplastic process]].<ref>{{Cite book| vauthors = Goodman LR |title=Felson's principles of chest roentgenology.|publisher=Elsevier|year=2015|isbn=978-0-323-77795-7|edition=Fifth|location=Philadelphia, Pennsylvania|pages=Supplement 3, e36-e80|oclc=1134689400}}</ref> When a substance other than air fills an area of the lung it increases that area's density. On both x-ray and CT, this appears more grey or hazy as opposed to the normally dark-appearing lungs. Although it can sometimes be seen in normal lungs, common pathologic causes include [[infection]]s, [[interstitial lung disease]], and [[pulmonary edema]].<ref name="Mettler_2019">{{Cite book | vauthors = Mettler Jr FA |title=Essentials of radiology |publisher=Elsevier |year=2019 |isbn=978-0-323-56787-9 |edition=Fourth |location=Philadelphia, Pennsylvania |pages=299–331 |oclc=1053711279}}</ref><ref name=":0">{{Cite book | vauthors = Sharma A, Abbott G |title=Thoracic imaging |publisher=Elsevier |year=2019 |isbn=978-0-323-59699-2 |edition=Third |location=Philadelphia, Pennsylvania |oclc=1022265855}}</ref>
== Definition == In both CT and chest radiographs, normal lungs appear dark due to the relative lower [[density]] of air compared to the surrounding tissues. When air is replaced by another substance (e.g. fluid or fibrosis), the density of the area increases, causing the [[Tissue (biology)|tissue]] to appear lighter or more grey.<ref>{{Cite book | vauthors = Herring W |title=Learning radiology : recognizing the basics |publisher=Elsevier |year=2020 |isbn=978-0-323-56728-2 |edition=4th |location=Philadelphia |pages=2–4 |oclc=1096282271}}</ref>
Ground-glass opacity is most often used to describe findings in [[High-resolution computed tomography|high-resolution CT]] imaging of the [[thorax]], although it is also used when describing chest radiographs. In CT, the term refers to one or multiple areas of increased [[attenuation]] (density) ''without'' concealment of the [[Pulmonary circulation|pulmonary vasculature]]. This appears more grey, as opposed to the normally dark-appearing (air-filled) lung on CT imaging. In chest radiographs, the term refers to one or multiple areas in which the normally darker-appearing (air-filled) lung appears more opaque, hazy, or cloudy. Ground-glass opacity is in contrast to [[Pulmonary consolidation|consolidation]], in which the pulmonary vascular markings are obscured.<ref name=":0" /><ref name=":1">{{Cite book | vauthors = Walker CM, Chung JH |title=Müller's imaging of the chest |publisher=Elsevier |year=2019 |isbn=978-0-323-53179-5 |edition=2nd |location=Philadelphia, Pennsylvania |pages=109–137 |oclc=1051135278}}</ref> GGO can be used to describe both focal and diffuse areas of increased density.<ref name=":1" /> Subtypes of GGOs include diffuse, nodular, centrilobular, mosaic, crazy paving, halo sign, and reversed halo sign.<ref name=":22">{{cite journal | vauthors = El-Sherief AH, Gilman MD, Healey TT, Tambouret RH, Shepard JA, Abbott GF, Wu CC | title = Clear vision through the haze: a practical approach to ground-glass opacity | journal = Current Problems in Diagnostic Radiology | volume = 43 | issue = 3 | pages = 140–58 | date = 2014 | pmid = 24791617 | doi = 10.1067/j.cpradiol.2014.01.004 }}</ref>
==Causes== The [[differential diagnosis]] for ground-glass opacities is broad. General etiologies include infections, interstitial lung diseases, pulmonary edema, [[pulmonary hemorrhage]], and neoplasm. A correlation of imaging with a patient's clinical features is useful in narrowing the diagnosis.<ref name=":22"/><ref name=":6">{{cite journal | vauthors = Parekh M, Donuru A, Balasubramanya R, Kapur S | title = Review of the Chest CT Differential Diagnosis of Ground-Glass Opacities in the COVID Era | journal = Radiology | pages = E289–E302 | date = July 2020 | volume = 297 | issue = 3 | pmid = 32633678 | pmc = 7350036 | doi = 10.1148/radiol.2020202504 }}</ref> GGOs can be seen in normal lungs. Upon expiration there is less air in the lungs, leading to a relative increase in density of the tissue, and thus increased attenuation on CT. Furthermore, when a patient lays supine for a CT scan, the posterior lungs are in a dependent position, causing partial collapse of the posterior [[Pulmonary alveolus|alveoli]]. This leads to an increase in density of the tissue, resulting increased attenuation and a possible ground-glass appearance on CT.<ref name=":0" />
=== Infectious causes === In the setting of [[pneumonia]], the presence of GGO (as opposed to consolidation) is a useful diagnostic clue. Most bacterial infections lead to lobar consolidation, while [[atypical pneumonia]]s may cause GGOs. While many of the pulmonary infections listed below may lead to GGOs, this does not occur in every case.<ref name = "Mettler_2019" /><ref name=":22"/><ref name=":6" /><ref>{{cite journal | vauthors = Rossi SE, Erasmus JJ, McAdams HP, Sporn TA, Goodman PC | title = Pulmonary drug toxicity: radiologic and pathologic manifestations | journal = Radiographics | volume = 20 | issue = 5 | pages = 1245–59 | date = 2000-09-01 | pmid = 10992015 | doi = 10.1148/radiographics.20.5.g00se081245 }}</ref><ref name=":8">{{cite journal | vauthors = Park CM, Goo JM, Lee HJ, Lee CH, Chun EJ, Im JG | title = Nodular ground-glass opacity at thin-section CT: histologic correlation and evaluation of change at follow-up | journal = Radiographics | volume = 27 | issue = 2 | pages = 391–408 | date = 2007-03-01 | pmid = 17374860 | doi = 10.1148/rg.272065061 | url = http://radiographics.rsna.org/content/27/2/391.long | url-access = subscription }}</ref>
[[File:CT_of_infiltrates_of_pneumocystis_pneumonia.jpg|thumb|413x413px|High-Resolution CT image in a patient with Pneumocystis pneumonia infection showing ground-glass opacities.]]
==== Bacterial ==== * Diffuse ** ''[[Mycoplasma pneumoniae]]'' ** ''[[Chlamydia pneumoniae]]'' ** ''[[Legionella pneumophila]]'' * Focal or nodular ** ''[[Mycobacterium]]'' ** ''[[Nocardia]]'' ** [[Septic embolism|Septic emboli]]
==== Viral ==== * [[Adenoviridae|Adenovirus]] * [[Coronavirus]] (including [[Middle East respiratory syndrome–related coronavirus|MERS-CoV]], [[Severe acute respiratory syndrome coronavirus|SARS-CoV]], and [[Severe acute respiratory syndrome coronavirus 2|SARS-CoV-2]]) * [[Cytomegalovirus|Cytomegalovirus (CMV)]] * [[Herpes simplex virus|Herpes Simplex Virus (HSV)]] * [[Human metapneumovirus|Human metapneumovirus (HMPV)]] * [[Influenza]][[File:Fibrosis focal intersticial.jpg|thumb|411x411px|CT image showing ground-glass opacification in the posterior of the right lung (screen left).]] * [[Measles]] * [[Respiratory syncytial virus|Respiratory Syncytial Virus (RSV)]] * [[Varicella zoster virus|Varicella zoster]]
==== Fungal ==== * ''[[Pneumocystis jirovecii]]'' (PCP) * [[Aspergillosis|Invasive aspergillosis]] * [[Candidiasis]] * [[Mucormycosis]] * [[Cryptococcus|Pulmonary cryptococcus]] * [[Paracoccidioidomycosis]]
==== Parasitic ==== * [[Schistosomiasis|Pulmonary Schistosomiasis]]
=== Non-infectious causes === [[File:Patron de ground glass parcheado.jpg|thumb|411x411px|CT image showing patchy areas of ground-glass opacities representing pulmonary edema.]]
==== Exposures ==== * [[Aspiration pneumonia|Aspiration pneumonitis]] * [[Adverse drug reaction|Drug toxicity]] (most common include [[cyclophosphamide]], [[amiodarone]], [[carmustine]], [[methotrexate]], and [[bleomycin]]) * [[Hypersensitivity pneumonitis]] * [[Vaping-associated pulmonary injury|EVALI]] * [[Radiation-induced lung injury|Radiation pneumonitis]]
==== Idiopathic interstitial pneumonia ==== * [[Acute interstitial pneumonitis]] * [[Desquamative interstitial pneumonia]] * [[Lymphocytic interstitial pneumonia]] * [[Non-specific interstitial pneumonia]] * [[Cryptogenic organizing pneumonia]]
==== Neoplastic processes ==== * [[File:Lung abscess - CT scan (7471756882).jpg|thumb|410x410px|CT image showing diffuse GGOs throughout both lungs. An abscess is also noted in the right lung (screen left).]][[Adenocarcinoma of the lung|Lung adenocarcinoma]] * [[Adenocarcinoma in situ of the lung]] * [[Atypical adenomatous hyperplasia]]
==== Additional causes ==== * [[Acute eosinophilic pneumonia]] * Cholesterol granulomas * Focal interstitial fibrosis * [[Granulomatosis with polyangiitis]] * [[Lymphomatoid granulomatosis|Lymphatoid granulomatosis]] * [[Pulmonary alveolar proteinosis]] * Pulmonary calcifications * [[Pulmonary capillary hemangiomatosis]] * [[Pulmonary contusion]] * [[Pulmonary edema]] * [[Pulmonary hemorrhage]] * [[Lung infarction|Pulmonary infarction]] * [[Sarcoidosis]] * [[Thoracic endometriosis]]
== Patterns == There are seven general patterns of ground-glass opacities.<ref name=":22"/> When combined with a patient's clinical signs and symptoms, the GGO pattern seen on imaging is useful in narrowing the differential diagnosis. It is important to note that while some disease processes present as only one pattern, many can present with a mixture of GGO patterns.<ref name=":22"/>
=== Diffuse === The diffuse pattern typically refers to GGOs in multiple lobes of one or both lungs. Broadly, a diffuse pattern of GGO can be caused by displacement of air with fluid, inflammatory debris, or fibrosis. [[Pulmonary edema|Cardiogenic pulmonary edema]] and ARDS are common causes of a fluid-filled lung. [[Pulmonary hemorrhage|Diffuse alveolar hemorrhage]] is a rarer cause of diffuse GGO seen in some types of vasculitis, autoimmune conditions, and bleeding disorders.<ref name=":22"/>
[[Inflammation]] and fibrosis can also cause diffuse GGOs. [[Pneumocystis pneumonia|Pneumocystis]] pneumonia, an infection typically seen in [[Immunodeficiency|immunocompromised]] (e.g. patients with [[HIV/AIDS|AIDS]]) or [[Immunosuppression|immunosuppressed]] individuals, is a classic cause of diffuse GGOs. Many viral pneumonias and idiopathic interstitial pneumonias can also lead to a diffuse GGO pattern. Radiation pneumonitis, a side effect of pulmonary radiation therapy, can lead to pulmonary fibrosis and diffuse GGOs.<ref name=":22"/>
=== Nodular === There are numerous potential causes of nodular GGOs which can be broadly separated into benign and malignant conditions. Benign conditions potentially leading to the formation of nodular GGOs include aspergillosis, acute eosinophilic pneumonia, focal interstitial fibrosis, granulomatosis with polyangiitis, [[IgA vasculitis]], organizing pneumonia, pulmonary contusion, pulmonary cryptococcus, and thoracic endometriosis. Focal interstitial fibrosis presents a unique challenge when differentiating from malignant nodular GGOs on CT imaging. It is typically persistent over long-term imaging follow-up and shares a similar appearance to malignant nodular GGOs.<ref name=":8" />
Pre-malignant or malignant causes of nodular GGOs include adenocarcinoma, adenocarcinoma in situ, and atypical adenomatous hyperplasia (AAH). One large review study found that 80% of nodular GGOs which were present on repeated CT imaging represented either pre-malignant or malignant growths. Differentiating between pre-malignancy and malignancy on the basis of CT alone can pose a challenge to radiologists; however, there are several features that are indicative of pre-malignant nodules. AAH is a pre-malignant cause of nodular GGO and is more commonly associated with lower attenuation on CT and smaller nodule size (<10 mm) compared to adenocarcinoma.<ref name=":9">{{cite journal | vauthors = Lee HY, Choi YL, Lee KS, Han J, Zo JI, Shim YM, Moon JW | title = Pure ground-glass opacity neoplastic lung nodules: histopathology, imaging, and management | journal = AJR. American Journal of Roentgenology | volume = 202 | issue = 3 | pages = W224-33 | date = March 2014 | pmid = 24555618 | doi = 10.2214/AJR.13.11819 }}</ref> In addition, AAH often lacks the solid features and spiculated appearance that are often associated with malignant growths.<ref name=":8" /> In contrast, as adenocarcinoma becomes invasive it will more often cause retraction of adjacent pleura and may show an increase in vascular markings. Nodules >15 mm almost always represent an invasive adenocarcinoma.<ref name=":8" /><ref name=":9" />
=== Centrilobular === Centrilobular GGOs refer to opacities occurring within one or multiple secondary lobules of the lung, which consist of a respiratory bronchiole, small pulmonary artery, and the surrounding tissue.<ref name=":0" /> A defining feature of these GGOs is the lack of involvement of the interlobular septum. Potential causes of centrilobular GGOs include pulmonary calcifications from [[Metastasis|metastatic disease]], some types of idiopathic interstitial pneumonias, hypersensitivity pneumonitis, aspiration pneumonitis, cholesterol granulomas, and [[Pulmonary capillary hemangiomatosis|pulmonary capillary hemangiomastosis]].<ref name=":22"/>
=== Mosaic === A [[mosaic]] pattern of GGO refers to multiple irregular areas of both increased attenuation and decreased attenuation on CT. It is often the result of occlusion of small pulmonary arteries or obstruction of small airways leading to air trapping.<ref name=":22"/> Sarcoidosis is an additional cause of a mosaic GGOs due to the formation of granulomas in interstitial areas. This may coexist with granulomatosis with polyangiitis, leading to diffuse areas of increased attenuation with ground-glass appearance.<ref name=":22"/>
=== Crazy paving === The crazy paving pattern may occur when there is both interlobular and intralobular widening. This sometimes resembles a road paved with irregular bricks or tiles. It is typically diffuse, involving larger areas of one or multiple lobes. There are a variety of potential causes, including Pneumocystis pneumonia, late-stage adenocarcinoma, pulmonary edema, some types of idiopathic interstitial pneumonias, diffuse alveolar hemorrhage, sarcoidosis, and pulmonary alveolar proteinosis.<ref name=":22"/> COVID-19 has also been shown to occasionally cause GGOs with a crazy paving pattern.<ref name=":10" />
=== Halo sign === A halo sign refers to a GGO that fills the area around a consolidation or nodule. This is a most commonly seen in various types of pulmonary infections, including CMV pneumonia, tuberculosis, nocardia infection, some fungal pneumonias, and septic emboli. Schistosomiasis, a [[Parasitic disease|parasitic]] infection, also commonly presents with the halo sign. Important non-infectious causes include granulomatosis with polyangiitis, metastatic disease with pulmonary hemorrhage, and some types of idiopathic interstitial pneumonias.<ref name=":22"/>
===Reversed halo sign=== A reversed halo sign is a central ground-glass opacity surrounded by denser [[pulmonary consolidation|consolidation]]. According to published criteria, the consolidation should form more than three-fourths of a circle and be at least 2 mm thick.<ref name="radiopedia">{{cite web| vauthors = Foley R |display-authors=etal|title=Reversed halo sign (lungs)|url=https://radiopaedia.org/articles/reversed-halo-sign-lungs|access-date=2 January 2018|website=[[Radiopaedia]]}}</ref> It is often suggestive of [[cryptogenic organizing pneumonia|organizing pneumonia]],<ref name=":3">{{cite book| vauthors = Elicker BM, Webb WR |title=Fundamentals of High-Resolution Lung CT: Common Findings, Common Patterns, Common Diseases, and Differential Diagnosis|publisher=Lippincott Williams & Wilkins|year=2012|isbn=9781469824796}}</ref> but is only seen in about 20% of individuals with this condition.<ref name="radiopedia" /> It can also be present in [[lung infarction]] where the halo consists of hemorrhage,<ref name="WuSchmit 2017">{{cite journal|vauthors=Wu G, Schmit B, Arteaga V, Palacio D|year=2017|title=Medical image of the week: pulmonary infarction- the "reverse halo sign"|journal=Southwest Journal of Pulmonary and Critical Care|volume=15|issue=4|pages=162–163|doi=10.13175/swjpcc124-17|issn=2160-6773|doi-access=free}}</ref> as well as in infectious diseases such as [[paracoccidioidomycosis]], [[tuberculosis]], and [[aspergillosis]], as well as in [[granulomatosis with polyangiitis]], [[lymphomatoid granulomatosis]], and [[sarcoidosis]].<ref>{{cite book| vauthors = Karthikeyan D |url=https://books.google.com/books?id=UQdr8GE9kkwC&pg=PA256|title=High Resolution Computed Tomography of the Lungs: A Practical Guide|publisher=JP Medical Ltd|year=2013|isbn=9789350904084|page=256}}</ref><gallery widths="175" heights="175"> File:COVID-19 Pneumonie - 74m CTax - 003.jpg|CT showing diffuse ground-glass opacities in periphery of both lungs in patient with COVID-19. File:CT of ground glass lung nodule.png|CT image showing ground-glass nodule (circled). File:PulmonaryTB.png|CT image showing centrilobular pattern of GGOs in patient with pulmonary tuberculosis. Note the small, nodular areas of increased attenuation in both lungs. File:Neumonitis por hipersensibilidad 2.jpg|CT image showing mosaic attenuation pattern in patient with hypersensitivity pneumonitis. Note the alternating, patchy areas of increased and decreased attenuation, particularly in the left lung (screen right). File:Crazy paving pattern on chest CT scan.jpg|CT image showing crazy paving pattern of ground-glass opacities in both lungs. File:CT of a subpleural nodule.png|CT image showing halo sign in patient with pulmonary aspergillosis. Note ground-glass opacification surrounding the area of consolidation (circled). File:Chest CT with reversed halo sign.jpg|CT image of reversed halo sign in patient with organizing pneumonia. </gallery>
== COVID-19 == [[File:COVID-19 Pneumonie - 74m CTcor - 002.jpg|thumb|233x233px|CT image in patient with COVID-19 showing bilateral ground-glass opacities at the periphery of both lungs.]] Ground-glass opacity is among the most common imaging findings in patients with confirmed [[Coronavirus disease 2019|COVID-19]].<ref name=":4">{{cite journal | vauthors = Bao C, Liu X, Zhang H, Li Y, Liu J | title = Coronavirus Disease 2019 (COVID-19) CT Findings: A Systematic Review and Meta-analysis | journal = Journal of the American College of Radiology | volume = 17 | issue = 6 | pages = 701–709 | date = June 2020 | pmid = 32283052 | pmc = 7151282 | doi = 10.1016/j.jacr.2020.03.006 }}</ref><ref name=":7">{{cite journal | vauthors = Salehi S, Abedi A, Balakrishnan S, Gholamrezanezhad A | title = Coronavirus Disease 2019 (COVID-19): A Systematic Review of Imaging Findings in 919 Patients | journal = AJR. American Journal of Roentgenology | volume = 215 | issue = 1 | pages = 87–93 | date = July 2020 | pmid = 32174129 | doi = 10.2214/AJR.20.23034 | doi-access = free }}</ref> One systematic review found that among patients with COVID-19 and abnormal lung findings on CT, greater than 80% had GGOs, with greater than 50% having mixed GGOs and consolidation.<ref name=":4" /> GGOs with mixed consolidation has most often been found in elderly populations.<ref name=":5">{{cite journal | vauthors = Salehi S, Abedi A, Balakrishnan S, Gholamrezanezhad A | title = Coronavirus Disease 2019 (COVID-19): A Systematic Review of Imaging Findings in 919 Patients | journal = AJR. American Journal of Roentgenology | volume = 215 | issue = 1 | pages = 87–93 | date = July 2020 | doi = 10.2214/AJR.20.23034 | pmid = 32174129 | doi-access = free }}</ref> Several studies have described a pattern among initial, intermediate, and hospital discharge imaging findings in the disease course of COVID-19. Most commonly, initial CT imaging reveals bilateral GGOs at the periphery of the lungs. During initial stages, this is most often found in the lower lobes, although involvement of the upper lobes and right middle lobe has also been reported early in the disease course.<ref name=":4" /><ref name=":5" /> This is in contrast to the two similar coronaviruses, [[Severe acute respiratory syndrome|SARS]] and [[Middle East respiratory syndrome|MERS]], which more commonly involve only one lung on initial imaging.<ref>{{cite journal | vauthors = Ooi GC, Daqing M | title = SARS: radiological features | journal = Respirology | volume = 8 Suppl | issue = s1 | pages = S15-9 | date = November 2003 | pmid = 15018128 | pmc = 7169195 | doi = 10.1046/j.1440-1843.2003.00519.x }}</ref><ref>{{cite journal | vauthors = Das KM, Lee EY, Langer RD, Larsson SG | title = Middle East Respiratory Syndrome Coronavirus: What Does a Radiologist Need to Know? | journal = AJR. American Journal of Roentgenology | volume = 206 | issue = 6 | pages = 1193–201 | date = June 2016 | pmid = 26998804 | doi = 10.2214/AJR.15.15363 | doi-access = free }}</ref> As the COVID-19 infection progresses, GGOs typically become more diffuse and often progress to consolidation.<ref name=":10">{{cite journal | vauthors = Ye Z, Zhang Y, Wang Y, Huang Z, Song B | title = Chest CT manifestations of new coronavirus disease 2019 (COVID-19): a pictorial review | journal = European Radiology | volume = 30 | issue = 8 | pages = 4381–4389 | date = August 2020 | pmid = 32193638 | pmc = 7088323 | doi = 10.1007/s00330-020-06801-0 }}</ref><ref name=":5" /> This is sometimes accompanied by the development of a crazy paving pattern and interlobular septal thickening.<ref name=":5" /> In many cases the most severe pulmonary CT abnormalities occurred within 2 weeks after symptoms began.<ref name=":7" /> At this point, many individuals begin showing resolution of consolidation and GGOs as symptoms improve. However, some patients have worsening symptoms and imaging findings, with further increase in septal thickening, GGOs, and consolidation. These patients may develop lung "white-out" with progression to [[Acute respiratory distress syndrome|acute respiratory distress syndrome (ARDS)]] requiring treatment escalation.<ref name=":7" /><ref>{{cite journal | vauthors = Carotti M, Salaffi F, Sarzi-Puttini P, Agostini A, Borgheresi A, Minorati D, Galli M, Marotto D, Giovagnoni A | display-authors = 6 | title = Chest CT features of coronavirus disease 2019 (COVID-19) pneumonia: key points for radiologists | journal = La Radiologia Medica | volume = 125 | issue = 7 | pages = 636–646 | date = July 2020 | pmid = 32500509 | pmc = 7270744 | doi = 10.1007/s11547-020-01237-4 }}</ref>
Preliminary reports have shown many patients have residual GGOs at time of discharge from the hospital. Due to the novelty of COVID-19, large studies investigating the long-term pulmonary CT changes have yet to be completed.{{Update-inline|date=February 2026}} However, long-term pulmonary changes have been seen in patients after recovery from SARS and MERS, suggesting the possibility of similar long-term complications in patients who have recovered from acute COVID-19 infection.<ref>{{cite journal | vauthors = George PM, Barratt SL, Condliffe R, Desai SR, Devaraj A, Forrest I, Gibbons MA, Hart N, Jenkins RG, McAuley DF, Patel BV, Thwaite E, Spencer LG | display-authors = 6 | title = Respiratory follow-up of patients with COVID-19 pneumonia | journal = Thorax | volume = 75 | issue = 11 | pages = 1009–1016 | date = November 2020 | pmid = 32839287 | pmc = 7447111 | doi = 10.1136/thoraxjnl-2020-215314 }}</ref>
== History == The first usage of "ground-glass opacity" by a major radiological society occurred in a 1984 publication of the ''American Journal of Roentgenology.'' It was published as part of a glossary of recommended nomenclature from the [[Fleischner Society]], a group of thoracic imaging radiologists.<ref name=":11">{{cite journal | vauthors = Tuddenham WJ | title = Glossary of terms for thoracic radiology: recommendations of the Nomenclature Committee of the Fleischner Society | journal = AJR. American Journal of Roentgenology | volume = 143 | issue = 3 | pages = 509–17 | date = September 1984 | pmid = 6380245 | doi = 10.2214/ajr.143.3.509 | doi-access = }}</ref> The original published definition read as: "Any extended, finely granular pattern of pulmonary opacity within which normal anatomic details are partly obscured; from a fancied resemblance to etched or abraded glass."<ref name=":11" /> It was again included in an updated glossary by the Fleischner Society in 2008 with a more detailed definition.<ref>{{cite journal | vauthors = Hansell DM, Bankier AA, MacMahon H, McLoud TC, Müller NL, Remy J | title = Fleischner Society: glossary of terms for thoracic imaging | journal = Radiology | volume = 246 | issue = 3 | pages = 697–722 | date = March 2008 | pmid = 18195376 | doi = 10.1148/radiol.2462070712 }}</ref>
== See also == * [[Pulmonary consolidation]] * [[Pulmonary infiltrate]]
== References == {{reflist}}
== External links == * [http://www.ajronline.org/content/160/2/249.full.pdf Ground-Glass Opacity of the Lung Parenchyma: A Guide to Analysis with High-Resolution CT] {{Radiologic signs}} {{Authority control}} [[Category:Radiologic signs]]