Introduction

As noted in Part 1 of this series, the term autoinflammatory disorders was originally used to differentiate autoimmune disorders from diseases with no specific autoantibodies or autoreactive lymphocytes, which were thought to be induced by innate rather than adaptive immune dysregulation [1]. However, today we know that there is overlap in the immunological characteristics of some of these entities with the classical autoimmune diseases [2].

Autoinflammatory diseases are further divided into monogenic and polygenic autoinflammatory syndromes, depending on whether there is an identified genetic mutation. Monogenic autoinflammatory syndromes are those with identified genetic mutations and are primarily errors of innate immunity. Those without an identified genetic mutation have a polygenic origin and include systemic-onset juvenile idiopathic arthritis, idiopathic recurrent acute pericarditis, Behçet syndrome, chronic recurrent multifocal osteomyelitis and inflammatory bowel disease [3].

The pathogenetic mechanisms underlying autoinflammation, although still unclear and different from each other from a molecular point of view, are responsible for an aberrant activation of the immune system resulting in involvement of multiple organs and systems. Symptoms are nonspecific and include recurrent flares or persistent systemic inflammation, fever, skin rashes, chest and abdominal pain, lymphadenopathy and arthritis. Because of the rarity of autoinflammatory diseases, their varied and nonspecific presentation, and the new genetic identification, diagnosis is usually delayed. Imaging can help provide clues for the diagnosis but the major role of imaging is to delineate organ involvement and disease extent.

In Part 2 of this series, we review the main polygenic autoinflammatory diseases in childhood, with special emphasis on imaging features that may be useful to reach the correct diagnosis.

Systemic-onset juvenile idiopathic arthritis

The systemic form of juvenile idiopathic arthritis is one of the most severe forms of juvenile idiopathic arthritis. According to the International League of Associations for Rheumatology criteria, systemic-onset juvenile idiopathic arthritis is characterized by arthritis with or preceded by at least 2 weeks of fevers that have been daily for at least 3 days, with at least one of the following: transitory rash, generalized lymphadenopathy, hepato- or splenomegaly, or serositis [4].

Arthritis, which is mandatory for a conclusive diagnosis, is not usually one of the presenting symptoms. In addition, the classical symmetrical and polyarticular joint involvement may not develop until late in the disease course [5]. Wrists, knees and ankles are frequently affected, although the hands, hips, cervical spine and temporomandibular joints can also be involved [6] (Fig. 1). Unlike the oligoarticular and polyarticular subtypes of juvenile idiopathic arthritis, the arthritis of systemic-onset juvenile idiopathic arthritis may start in the hips and can progress very rapidly, causing severe damage and dysfunction resulting in the need for early joint replacement surgery as well as loss of growth potential in younger patients. The imaging findings are summarized in Table 1. The main radiologic findings in systemic-onset juvenile idiopathic arthritis are juxta-articular osteopenia, joint space narrowing, erosions, growth abnormalities and even ankylosis (Fig. 2). Generalized delay in bone age is also common. Ultrasonography (US) is very helpful to evaluate tenosynovitis, which is common in children with polyarticular course and is characterized by increased fluid content within the tendon sheath and hypoechoic thickening of the synovial sheath with or without increased vascularity [6]. Magnetic resonance imaging (MRI) with intravenous contrast administration is the technique of choice to study arthritis [7]. It has the advantages of displaying both soft tissue and bone, being the most sensitive technique for detecting acute synovitis and tenosynovitis, and the only one able to identify bone marrow edema. Furthermore, it allows detection of changes in the joint over time and evaluates the effectiveness of therapeutic interventions. On MRI, tenosynovitis appears as increased fluid within the tendon sheath, with low or intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images, or as increased enhancement of the tendon sheath. The most frequently affected tendons are the extensor tendons of the carpus, the flexor tendons of the fingers, the extensor tendons of the feet, and the posterior tibialis and peroneus tendons [6]. Occasionally, synovial cysts that communicate with the shoulder, elbow, wrist or knee joints are also seen [6]. Myositis is rare but can be identified by MRI [8].

Fig. 1
figure 1

Systemic-onset juvenile idiopathic arthritis in a 10-year-old girl with daily fever, arthralgias for 1 year and a history of pericarditis. a Posteroanterior radiograph of the chest and abdomen shows mediastinal widening (arrow) and hepatosplenomegaly (asterisks). b Axial contrast-enhanced computed tomography (CT) image of the chest confirms multiple enlarged mediastinal lymph nodes (arrows). c Axial contrast-enhanced CT image of the abdomen shows several enlarged lymph nodes at the splenic hilum (arrowheads). d, e Four years later, the child presented with deviation of the mandible to the right on the mouth opening. Sagittal T2-weighted gradient echo magnetic resonance imaging (MRI) of the right temporomandibular joint (d) shows an erosion in the mandibular condyle (arrowhead), bone marrow edema (arrow) and intra-articular high signal intensity that may represent joint effusion or synovial thickening (curved arrow). Axial contrast-enhanced fat-suppressed T1-weighted MRI of both temporomandibular joints (e) shows thickening and enhancement of the synovium on the right, consistent with active synovitis (curved arrow) combined with joint effusion (arrowhead). f Three years later, the child presented with left hip pain. Coronal contrast-enhanced fat-suppressed T1-weighted MRI of the hips shows left proximal femoral bone marrow enhancement and marked synovial thickening and enhancement of the left hip joint (arrow)

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Table 1 Findings in polygenic autoinflammatory diseases
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Fig. 2
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Systemic-onset juvenile idiopathic arthritis in an 11-year-old boy with left hand pain on flexion. a, b Anteroposterior radiograph (a) and coronal T1-weighted MRI (b) of the left hand show carpal and carpometacarpal joint bony ankylosis (arrowheads). There is also shortening and deformity of the left ulna (arrow in a). These are all sequelae of synovitis and erosive changes

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Pericardial effusion is common and frequently asymptomatic, with no obvious cardiomegaly or typical electrocardiographic findings [9]. Myocarditis is much less common.

Pleural effusion, the most common chest manifestation, is frequently found incidentally on chest radiographs [6]. Interstitial lung disease, alveolar proteinosis and pulmonary hypertension are rare but are being reported with increasing frequency [10].

Lymphadenopathy and splenomegaly may occur alone or together and are characteristic of systemic-onset juvenile idiopathic arthritis (Fig. 1). Lymphadenopathy might be markedly enlarged and symmetrically distributed, especially in the cervical, axillary and inguinal regions, and thus it mimics the appearance of lymphoma [6]. Hepatomegaly is not as frequent as splenomegaly [6] (Fig. 1). Occasionally, a fatty liver can be seen secondary to glucocorticoid administration, but chronic hepatic disease generally does not occur.

Acute neurological episodes such as macrophage activation syndrome and posterior reversible encephalopathy syndrome are uncommon but serious complications in children with systemic-onset juvenile idiopathic arthritis [6]. Macrophage activation syndrome is an acute, life-threatening condition characterized by pancytopenia, disseminated intravascular coagulopathy, hepatic dysfunction and persistent fever resulting in multiorgan failure. Brain MRI may show intracranial hemorrhages and cerebral edema [11]. Posterior reversible encephalopathy syndrome consists of a neurotoxic state secondary to the inability of the circulation to autoregulate in response to acute changes in blood pressure [12]. MRI shows symmetrical brain edema at the watershed zones, most common in the parietal and occipital cortical and subcortical areas (Fig. 3). These findings are usually reversible.

Fig. 3
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Systemic-onset juvenile idiopathic arthritis and macrophage activation syndrome in a 10-year-old girl with seizures. a Coronal fluid-attenuated inversion recovery (FLAIR) MRI of the brain shows bilateral occipital cortical high signal intensity (arrows). b Axial diffusion-weighted MRI shows diffusion restriction of the bilateral occipital lesions (arrows). These findings are in keeping with posterior reversible encephalopathy syndrome

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Treatment of systemic-onset juvenile idiopathic arthritis includes the use of nonsteroidal anti-inflammatory drugs, oral or intravenous glucocorticoids and biological agents.

Idiopathic recurrent acute pericarditis

The term recurrent pericarditis is used when there is a second episode of acute pericarditis after a period of at least 4 to 6 weeks from an initial episode with no symptoms in between [13]. If the symptoms last more than 3 months, it is then called chronic pericarditis [14].

The most frequent imaging finding is pericardial effusion (Table 1) (Fig. 4). Transthoracic echocardiography is generally the initial diagnostic imaging study performed in these children, but cardiac MRI is better suited to evaluate inflammatory changes. The presence and extent of late gadolinium enhancement of the pericardium are indicators of pericarditis and are useful in guiding the anti-inflammatory treatment [15].

Fig. 4
figure 4

Acute recurrent pericarditis in a 15-year-old boy with recurrent episodes of asthenia, fever and dyspnea. a Anteroposterior radiograph of the chest shows enlargement of the cardiac silhouette. b Axial contrast-enhanced CT image of the chest shows a large pericardial effusion (arrows) and bilateral pleural effusions (arrowheads). c Posteroanterior radiograph of the chest after treatment shows normal cardiac silhouette

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In contrast to the first episode of acute pericarditis, treatment of idiopathic recurrent acute pericarditis should include a new course of nonsteroidal anti-inflammatory drugs with additional colchicine for 6 months. Anti-tumor necrosis factor-alpha drugs and Interleukin-1 blockade have also been used with good clinical response [16].

Behçet disease

Behçet disease is categorized as an inflammatory vascular disease affecting arteries and veins of all kinds and sizes, and is characterized by recurrent oral and genital aphthae, ocular, cutaneous, gastrointestinal, neurological, vascular and/or articular involvement [17].

One of the major characteristic features of Behçet disease is the heterogeneity of the clinical presentation. Imaging findings in Behçet disease are summarized in Table 1. Barium study was traditionally useful in demonstrating the presence of deep, penetrating ulcers, which are characteristic radiographic features of this disease in the gastrointestinal tract. The progression of this penetrating disease may result in multiple complications, including perforation, fistula, hemorrhage and peritonitis [18]. Currently, computed tomography (CT) and MR enterography are used to diagnose Behçet disease, with typical findings including bowel wall thickening and enhancement associated with deep penetrating ulcers, particularly in the ileocecal region. Polypoid appearance of the intestinal surface and homogeneous enhancement of the small-bowel wall are more common in children with Behçet disease than in patients with Crohn disease [19]. A layered or stratified enhancement pattern, the presence of strictures, and the involvement of a long segment and, particularly, of more proximal ileal segments favor Crohn disease [19]. However, in the absence of extraintestinal manifestations, it may be impossible to differentiate intestinal Behçet disease from Crohn disease. On occasion, Behçet disease can manifest as a cecal mass or an aneurysmal dilatation of the terminal ileum mimicking a malignant tumor, particularly lymphoma [20,21,22].

Cardiopulmonary and renal involvement is rare in children. Neurological manifestations may include encephalomyelitis or aseptic meningitis (Fig. 5), as well as dural sinus thrombosis (Fig. 6). Oligoarthritis is common, usually asymmetrical and nonerosive and most frequently affects medium and large joints including the knees, ankles, wrists and elbows. Myositis is uncommon. The vasculitis of Behçet disease is characterized by venous thrombosis and arterial occlusions or aneurysms [23, 24]. Thrombosis of the hepatic veins can result in Budd-Chiari syndrome [23, 24].

Fig. 5
figure 5

Behçet disease in a 10-year-old girl with recurrent fever and meningoencephalitis. a Coronal fluid-attenuated inversion recovery (FLAIR) MRI of the brain at presentation shows high signal intensity in the midbrain, extending into the cerebral peduncles and pons (arrow). There was associated leptomeningeal enhancement and central punctate enhancement at the right cerebral peduncle (not shown). b Coronal FLAIR MRI of the brain at the 7-month follow-up shows a normal appearance with resolution of the previous findings

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Fig. 6
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Behçet disease in a 12-year-old boy with constitutional symptoms and diplopia. Axial (a) and coronal (b) contrast-enhanced CT images of the brain show a tubular filling defect in the right sigmoid sinus consistent with venous sinus thrombosis (arrows)

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Treatment of Behçet disease is variable, depending on the location and severity of involvement. Topical treatment with sucralfate suspension or corticosteroids is used initially for ulcers [23]. Prednisone is frequently the first treatment option for multiple manifestations. Azathioprine and biologics, mainly tumor necrosis factor-alpha blocking agents, are useful for uveitis. Low-dose methotrexate, azathioprine, anti-tumor necrosis factor agents and cyclophosphamide are helpful for central nervous system disease [23].

Chronic recurrent multifocal osteomyelitis

Chronic recurrent multifocal osteomyelitis, also named chronic nonbacterial osteomyelitis, is a rare type of skeletal inflammation that occurs mainly in children and adolescents, affects females more frequently and shows a worldwide distribution.

Chronic recurrent multifocal osteomyelitis remains a diagnosis of exclusion, as no specific diagnostic test is available [25]. Infectious osteomyelitis and neoplasms such as osteosarcoma, Ewing sarcoma, lymphoma, neuroblastoma, leukemia, Langerhans cell histiocytosis, osteoid osteoma and osteoblastoma are often part of the differential diagnosis (Table 2) [4, 25,26,27,28,29,30,31,32,33,34,35,36,37,38]. Multiple bone lesions, a relapsing-remittent course, involvement of locations not typical for infectious osteomyelitis, such as the clavicle, imaging findings in keeping with subacute or chronic osteomyelitis but with no abscess, fistula or sequestrum, absence of an infectious microorganism and improvement with nonsteroidal anti-inflammatory drugs but not antibiotics suggest the diagnosis [25, 39, 40]. In addition, chronic recurrent multifocal osteomyelitis may be associated with other inflammatory disorders of the skin, such as pustulosis palmoplantaris or acne, as well as gastrointestinal tract diseases, including inflammatory bowel disease, and vasculitis such as Takayasu arteritis and granulomatosis with polyangiitis (formerly known as Wegener granulomatosis) [25].

Table 2 Imaging differential diagnosis of chronic recurrent multifocal osteomyelitis
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Chronic recurrent multifocal osteomyelitis is usually bilateral and multifocal at presentation but often lacks clinical and temporal symmetry [25]. Typical imaging findings (Table 1) consist of lytic and sclerotic metaphyseal lesions in the long bones, especially involving the lower extremities and the medial aspect of the clavicles (Fig. 7) [39]. In fact, involvement of the clavicles is one of the distinctive features of chronic recurrent multifocal osteomyelitis, which is a rare location for hematogenous osteomyelitis. In addition, excluding neoplastic processes, chronic recurrent multifocal osteomyelitis is the most frequent disease affecting the clavicle in children and young adults, as well as the most frequent pathology involving the medial third of the clavicle at any age [25]. As opposed to synovitis-acne-pustulosis-hyperostosis-osteitis (SAPHO) syndrome, clavicular disease in chronic recurrent multifocal osteomyelitis is not associated with the sternoclavicular joint. In addition to the clavicle and long bones, involvement of the vertebral bodies, pelvis, ribs, and mandible is also common [25].

Fig. 7
figure 7

Chronic recurrent multifocal osteomyelitis in a 15-year-old girl with left shoulder pain. a Posteroanterior radiograph of the upper chest shows enlargement and sclerosis of the medial aspect of the left clavicle (arrow), a common site of involvement in chronic recurrent multifocal osteomyelitis. b Axial CT image shows thickening of the left clavicle with a mixed pattern of lysis and sclerosis

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At presentation, radiographs may be completely normal or show only osteopenia, however, MRI may show bone marrow edema at this stage. With time, radiographs typically show a metaphyseal osteolytic lesion abutting the growth plate demarcated by a thin sclerotic rim (Fig. 8) [41]. With disease progression, sclerosis gradually increases around the lytic lesion and therefore chronic lesions usually become mainly sclerotic with associated hyperostosis [25]. Lesions also occur in nontubular bones, in metaphyseal-equivalent regions adjacent to cartilage.

Fig. 8
figure 8

Chronic recurrent multifocal osteomyelitis in a 15-year-old boy with polyarticular pain that is more prominent in the right knee. a Anteroposterior radiograph of the right knee shows widening and irregularity of the medial aspect of the proximal tibial physis (arrowhead) and an ill-defined lesion in the adjacent metaphysis (arrow). b Coronal reformatted CT image of the right proximal tibia shows a focal lytic lesion at the medial aspect of the proximal metaphysis (arrow). c Coronal short tau inversion recovery (STIR) MRI of the knees shows increased signal intensity involving the proximal epiphysis, metaphysis and diaphysis of the right tibia (arrow), as well as the distal epiphysis of both femurs (arrowheads), more extensive on the left

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MRI may suggest the diagnosis and show the typical periphyseal, multifocal pattern [42]. It can also detect clinically occult involvement and show the extension of the bone and soft-tissue lesions (Fig. 9). Whole-body MRI with short tau inversion recovery (STIR) images is the imaging technique of choice used at our institution as it allows identification of asymptomatic lesions and establishes a baseline of disease burden [43]. The protocol includes coronal images of the whole body and sagittal images of the spine. Whole-body imaging can also be done with Technetium-99 bone scintigraphy, which shows areas of increased uptake. However, MRI is preferred because of the lack of radiation and the better assessment of the anatomy and soft tissues [44]. Furthermore, the physiological uptake of the physis seen on the bone scan can be misleading. Positron emission tomography has been used clinically to detect chronic osteomyelitis, but its use in chronic recurrent multifocal osteomyelitis has not been described [45]. In addition to the typical metaphyseal involvement, accompanying epiphyseal lesions are also frequent [42]. Recognizing transphyseal involvement and secondary physeal bars is important as it allows identifying children at higher risk for growth deformities [25]. Diaphyseal involvement is rare, although it usually occurs next to the affected metaphyses [46]. MRI may show periostitis, inflammatory changes in the adjacent soft tissues, involvement of the physis and articular inflammation with synovitis, joint effusion and destructive changes within the joint cartilage and subchondral bone [25]. Active lesions typically show increased signal intensity on STIR and fat-suppressed T2-weighted images, decreased signal intensity on T1-weighted images, and increased apparent diffusion coefficient values on diffusion-weighted imaging [47]. MRI is also useful for follow-up, particularly when there is suspicion for inflammatory activity in children with marked sclerosis or hyperostosis. In these patients, areas of sclerosis with no superimposed inflammation appear hypointense on T1- and T2-weighted images [25]. Findings such as abscess, fistula or sequestrum are more characteristic of infectious osteomyelitis rather than chronic recurrent multifocal osteomyelitis.

Fig. 9
figure 9

Chronic recurrent multifocal osteomyelitis in an 11-year-old girl with a 3-week history of persistent left hip pain, daily fevers and weight loss. a Coronal STIR whole-body MRI at presentation shows hyperintense foci in the left acetabulum and adjacent iliac bone (long arrow) and ischium, adjacent soft tissues (arrowhead) and right medial femoral condyle (short arrow). There is also a small left-side hip joint effusion (curved arrow). b Coronal STIR whole-body MRI 4 months later shows significant improvement in the signal abnormality within the left acetabulum and ischium (arrow) and resolution of the signal abnormality within the right distal femoral epiphysis. New bone marrow hyperintense foci are seen in the bilateral proximal tibial metaphyses (arrowheads)

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Nonsteroidal anti-inflammatory drugs represent the initial treatment option. Second-line treatment agents include corticosteroids, azathioprine, disease-modifying antirheumatic drugs, bisphosphonates, biologics, mainly tumor necrosis factor-alpha and Interleukin-1 blocking agents, and other immune modulators [41].

Inflammatory bowel disease

Inflammatory bowel disease is a chronic, relapsing autoinflammatory disease of the gastrointestinal tract, and is often categorized in three subtypes: Crohn disease, ulcerative colitis and unclassified [48]. Inflammatory bowel disease has a prevalence of 1 in 1,000 inhabitants in Western countries [48]. Approximately 25% of inflammatory bowel disease occurs in children [49], in whom Crohn disease tends to be more common than ulcerative colitis, especially in males [48].

Symptoms at presentation in children are diverse and include abdominal pain, diarrhea (with or without bloody stools), perianal lesions, growth retardation and weight loss [48]. Extraintestinal manifestations may be seen, including hepatobiliary, pancreatic, genitourinary, musculoskeletal, pulmonary, cardiac, ocular and dermatological symptoms.

Ulcerative colitis and Crohn disease have distinctive characteristics that help to establish a specific diagnosis. Crohn disease can involve the gastrointestinal tract from mouth to anus with multiple inflammatory lesions separated by normal bowel segments. In addition, these lesions may involve the entire bowel wall from the mucosa to serosa causing deep ulcerations and local complications, such as abscesses and fistulas [48]. Bowel strictures are also relatively frequent in Crohn disease. In contrast, in ulcerative colitis, lesions are limited to the mucosa and to the large bowel, and perianal lesions are uncommon and limited [48]. Unclassified inflammatory bowel disease refers to colitis with equivocal features for Crohn disease or ulcerative colitis.

The diagnosis of inflammatory bowel disease requires correlation of clinical, biological, endoscopic, histological and imaging findings [48] as shown in the revised Porto criteria proposed by the European Society for Paediatric Gastroenterology Hepatology and Nutrition [50, 51] and exclusion of potential mimickers (Table 3) [19, 52,53,54,55,56,57,58]. US and MRI are the imaging techniques most frequently used to diagnose and manage inflammatory bowel disease in children, although radiography, fluoroscopic studies and CT may also be useful [59]. The imaging findings in inflammatory bowel disease are summarized in Table 1. Transabdominal US may detect bowel inflammation and evaluate the severity and extent of the disease although its value is limited for the small bowel compared to MR enterography. Increased bowel wall thickness (>3 mm) is the main sonographic finding (Fig. 10) [60]. Other sonographic findings include hyperemia, abnormal bowel wall echogenicity, abnormal bowel margin, increased echogenicity of the surrounding fat and lymphadenopathy [50]. US may also depict complications such as inflammatory mass (phlegmon/abscess), stricture, sinus tract and fistula. MR enterography and CT have similar indications and diagnostic performance, but MR enterography is preferred in children due to the lack of ionizing radiation [50, 60]. MRI of the bowel needs fast acquisition techniques and luminal distension [61]. The main MRI findings are mural enhancement, wall thickening, intramural edema (T2 hyperintensity), ulcerations, sacculations, stricture, fistula, sinus tract, inflammatory phlegmon, abscess (fluid collection with enhancing rim with or without air, with diffusion restriction), perienteric edema/engorged vasa recta (comb sign), and mesenteric venous thrombosis [60] (Fig. 11). Diminished peristalsis may also be present in small bowel Crohn disease [62]. Extraintestinal findings such as sacroiliitis, sclerosing cholangitis, avascular necrosis, pancreatitis, nephrolithiasis, cholelithiasis and perianal disease can also be depicted.

Table 3 Differential diagnosis of inflammatory bowel disease
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Fig. 10
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Crohn disease in a 16-year-old boy with symptoms of small bowel obstruction. a Transverse sonogram of the right lower quadrant of the abdomen shows marked wall thickening of the terminal ileum (arrow), measuring 0.61 cm, with increased echogenicity of the adjacent fat (asterisk). b Transverse sonogram with color Doppler interrogation shows marked hyperemia of the thickened bowel wall, which is considered a sign of disease activity

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Fig. 11
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Crohn disease in a 9-year-old girl with abdominal pain and diarrhea. a Coronal fat-suppressed T2-weighted image shows marked wall thickening and edema of the terminal ileum (arrow). b Coronal diffusion-weighted MRI (b=800 s/mm2) shows thickening and increased signal intensity of the terminal ileum (arrowhead). c Coronal apparent diffusion coefficient map MRI shows the corresponding hypointensity of the terminal ileum consistent with marked diffusion restriction (arrowhead). d Axial fat-suppressed contrast-enhanced T1-weighted MRI shows increased enhancement of the thickened terminal ileum (curved arrow) denoting inflammation

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The current goals of treatment in inflammatory bowel disease are to eliminate symptoms and restore quality of life, restore normal growth and eliminate complications. Corticosteroids, enteral nutrition therapy, aminosalicylates, immunomodulators, anti-tumor necrosis factor therapy and surgery are the main therapeutic options [63].

Conclusion

Autoinflammatory diseases include a broad spectrum of disorders with a wide variety and, often, nonspecific presentations. Imaging provides clues for diagnosis and is useful to assess organ involvement and disease extent. Systemic-onset juvenile idiopathic arthritis is associated with arthritis, lymphadenopathy, hepatosplenomegaly and serositis. Idiopathic recurrent pericarditis is characterized by recurrent pericardial effusions. Behçet disease is characterized by deep penetrating ulcers, particularly in the ileocecal region, neurological vascular and articular involvement. Multiple bone lesions with predilection for the metaphyses of the lower extremities and the medial clavicles are typical of chronic recurrent multifocal osteomyelitis. Bowel wall thickening is the main finding in inflammatory bowel disease, although abdominal complications and extraintestinal findings may be detected on imaging.