Special article
Imaging findings of sarcoidosisHallazgos en las pruebas de imagen de la sarcoidosis☆

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Introduction

Sarcoidosis is a multisystem disease that affects populations throughout the world, characterized by an exaggerated and persistent Th1 immune system response that leads to the formation of non-caseating granulomas. It was first described in 1877 by Hutchinson, who described them as purple skin lesions, and which were later termed "sarcoids" by Boeck, due to their histological similarity to sarcoma.1, 2, 3, 4, 5

The aetiology of sarcoidosis is unknown. Its development requires genetic predisposition and interaction with environmental or infectious factors.5 Some authors consider that sarcoidosis is a family of different diseases, which would include Löfgren's syndrome, its progression to pulmonary fibrosis, sarcoid uveitis or cardiac involvement.5, 6 The clinical heterogeneity of sarcoidosis could be due to a hypothetical heterogeneity in its etiology.5

In terms of epidemiology, it has a worldwide distribution, affecting both sexes and with a highly variable incidence among different populations. An incidence of 35.5/100,000 has been described in the African American population of the USA, compared to 10.9/100,000 in the population of the UK.1, 2, 3, 4 Although there are not many epidemiological studies in Spain, the annual incidence rate described in the evaluation of a health area in León was 1.37/100,000 inhabitants, and the estimated cumulative annual incidence rate for the entire country was 1.36/100,000 inhabitants.2

Sarcoidosis typically occurs in individuals between the ages of 20 and 60. Although most patients have clinical manifestations, a non-negligible percentage of patients are asymptomatic and may be diagnosed incidentally due to findings on a chest X-ray and/or computed tomography (CT) performed for another reason. The most common involvement is pulmonary, followed by cutaneous and ocular manifestations. 90% of patients show pulmonary abnormalities, and only 10–30% have skin, ocular or peripheral lymphadenopathy at the time of diagnosis. However, its initial manifestation is extrapulmonary in more than 30%. In patients with exclusively pulmonary involvement, a differential diagnosis with more common diseases such as asthma or chronic bronchitis may be clinically considered, but the findings on chest X-ray or CT can be of great help to guide the diagnosis. In these cases, a diagnosis can be made earlier than in sarcoidosis with extrapulmonary involvement, which can suffer a longer delay.1, 2, 3

Typical clinical manifestations of sarcoidosis include: nonspecific respiratory symptoms such as dry cough, dyspnoea, and chest pain or discomfort (present in 9–50% of cases), asthenia, weight loss, fever or night sweats, muscle weakness or exercise intolerance. Lung auscultation is usually inconclusive, even when there is lung parenchymal involvement on imaging tests.1, 3, 7, 8

Patients with suspected sarcoidosis should undergo a complete physical examination, including an ophthalmological examination, chest X-ray, conventional blood tests including calcium, total protein and angiotensin converting enzyme, tuberculin test or quantiferon determination, respiratory function, including spirometry, lung volumes and CO diffusion capacity and electrocardiogram.1, 8

There is no definitive test for the diagnosis of sarcoidosis, which is based on a combination of different criteria: clinical presentation and compatible radiological findings, histopathological determination of non-caseating granulomas and other granulomatous diseases.3, 8, 9 This paper reviews the imaging tests of current utility in the diagnosis and management of sarcoidosis according to the different organ involvement of this disease.

Section snippets

Pulmonary sarcoidosis

More than 90% of patients with chest involvement show abnormalities in the chest X-ray. The most common finding is lymphadenopathy, which appear in 60–70% of cases, and between 20-50% present ground-glass opacities in the upper and middle areas of the lungs. Pulmonary lesions may resolve or progress to fibrosis.1, 3, 10

Hilar/mediastinal lymphadenopathy typically have a bilateral and symmetric distribution. This is the most common and characteristic finding of sarcoidosis, especially when it

Cardiac sarcoidosis

Cardiac sarcoidosis (CS) is a relevant cause of morbidity and mortality in patients with sarcoidosis. Although only 5% of patients with systemic sarcoidosis have cardiac involvement, some autopsy series studies have found a prevalence of subclinical CS of 25%, so cardiac involvement appears to be under-diagnosed.1 It is estimated that 16–35% of those under 60 years of age with atrioventricular block or ventricular tachycardia have underlying CS. Sarcoidosis can affect any part of the heart

Abdominal sarcoidosis

Sarcoidosis can affect any abdominal organ, but the liver, kidneys, spleen, and stomach are the most common.1, 18

Neurosarcoidosis

The most common manifestations of neurosarcoidosis are cranial nerve involvement, especially peripheral facial palsy, sometimes bilateral, and optic nerve involvement. Other manifestations are headache, aseptic meningitis (cerebrospinal fluid [CSF] with lymphocyte cellularity, elevated spinal fluid protein count and presence of oligoclonal bands in both CSF and serum), seizures, motor, or sensory signs due to space-occupying lesions, intracranial hypertension, hypothalamic-pituitary involvement

Sarcoidosis in the head and neck

Between 10-15% of patients with sarcoidosis show involvement of head and neck structures such as the orbits, salivary glands, paranasal sinuses, hypopharynx, thyroid, cervical ganglia and larynx.1, 18, 28

Between 25-50% of patients with sarcoidosis will develop ophthalmological abnormalities, which will be their first clinical manifestation in 20%, even prior to the onset of pulmonary abnormalities. The most common is uveitis, although any part of the eye, adnexa or orbit can develop bilateral

Musculoskeletal sarcoidosis

Sarcoidosis can affect any bone, joint, or muscle. Bone involvement has been described in 1–13% of patients, with a certain preference for small bones, especially middle and distal phalanges of the 2nd and 3rd finger. Small bone involvement (hands and feet) is characterized by osteolysis with thickening of the preserved bone trabeculae and cortical thinning, without periosteal reaction. Bone collapse or pathological fracture may occur. The involvement of long bones and the axial skeleton causes

Current significance of PET in sarcoidosis

18F-FDG PET/CT has proven to be a useful imaging technique in certain situations for the study and management of sarcoidosis. However, it is currently being used indiscriminately for the study and follow-up of cases of sarcoidosis that are not particularly complex. We consider PET to be especially useful in the following four situations. Firstly, for the study of complex clinical cases in which the diagnostic possibility of sarcoidosis is raised; although the most characteristic pattern is

Conclusions

Sarcoidosis is a multisystemic, non-caseating granulomatous disease with a worldwide distribution that affects men and women of all ages. Its cause is unknown but is attributed to the effect of environmental or infectious triggers on a genetically susceptible host in whom a disproportionate granulomatous response will develop. This paper provides a review of the different organ involvement in sarcoidosis from an imaging point of view, highlighting its most common forms of presentation, as well

Funding

This article has not received any type of funding.

Conflict of interests

The authors declare no conflict of interest.

Acknowledgements

The authors would like to thank the selfless collaboration of doctors J. Torres Nuez, G. Martínez Sanz, E. García Martínez and C. Soto Sarrión.

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    ☆

    Please cite this article as: Sánchez-Oro R, Meseguer Ripollés MÁ, Alonso-Muñoz EM, Alandete German SP. Hallazgos en las pruebas de imagen de la sarcoidosis. Med Clin (Barc). 2021;156:349–355.

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