|ECR 2019 / C-3390|
|When HRCT requires brain MRI: (intra)cranial manifestations in diffuse parenchymal lung diseases, a pictorial review|
Findings and procedure details
Sarcoidosis is a multisystem disorder characterized by the development of noncaseating granulomas, frequently found in relation with lymphatics. Often called the “great mimicker”, it can involve many organs with multiple clinical presentations, with most of them related to pulmonary, skin and ocular involvement . It typically presents in young and middle-age adults under the age of 50 years, although children and elderly may also be affected. The diagnosis is established when clinic-radiological findings are supported by histological evidence of noncaseating epithelioid granulomas (Fig. 1, 2) .
· Thoracic involvement:
Sarcoidosis affects the thorax in at least 90% of cases , most frequently manifesting with intrathoracic symmetric lymphadenopathy and pulmonary parenchymal changes, which are a manifestation of interstitial or airway granulomas. The variety of abnormalities that may be seen on HRCT include nodules, consolidation and masses, ground glass and confluent alveolar opacities (alveolar sarcoid), interlobular septal thickening and fibrocystic changes . Pulmonary fibrosis may develop in up to 25% of patients . The abnormalities predominate in the upper and middle zones of the lungs. Typically, pulmonary sarcoidosis presents with well-defined micronodules with typical perilymphatic distribution along the bronchovascular bundles and subpleural interstitium adjacent to fissures (Fig. 1A-B,Fig. 8A-B). Frequently clusters of peribronchovascular nodules can converge in an area of mass-like consolidation with individual nodules at the periphery of the lesion forming the “galaxy sign”, most commonly seen with sarcoidosis. The lymphadenopathy is typically symmetric in distribution, involving the hilar, paratracheal, aortopulmonary window and subcarinal regions (Fig. 1C,Fig. 8C). Lymph nodes may calcify (Fig. 1C, Fig. 8C), with the morphology of calcifications being dense, hazy or eggshell.
· Intracranial involvement:
Clinically silent involvement of the CNS occurs in approximately 25% of patients with sarcoidosis , but only 10% of all patients with sarcoidosis present with neurologic symptoms . CNS involvement can precede the diagnosis of sarcoidosis and may be initially suggested by imaging. Within the CNS the disease has a propensity to involve the basal meninges, cranial nerves, pituitary-hypothalamic axis, optic chiasm and the perivascular Virchow-Robin spaces.
The involvement of the pituitary-hypothalamic axis may be one of the first disease manifestation in form of diabetes insipidus (up to 90% of patients) and symptoms related to hyperprolactinemia, amenorrhea (patient in Fig. 5) or panhypopituitarism . Pituitary involvement may be present as enhancing intrasellar mass with suprasellar extension, abnormal enlargement and enhancement of the infundibulum (Fig. 5F, Fig. 9 C-F) and infiltrative enhancing lesions of the hypothalamus (Fig. 3). Additionally, a lack of the normal T1-weighted hyperintense signal of the posterior pituitary, related to the absence of vasopressin-containing granules, the so called “loss of bright spot”, can be present. There can be adjacent leptomeningeal enhancement (Fig. 3).
Leptomeningeal involvement is the most common manifestation of neurosarcoidosis. It has a predilection to involve the basal meninges, most commonly the suprasellar and frontal meninges (Fig. 4) and present as nodular thickening and enhancement on contrast enhanced T1-weighted images. There may be disruption of the blood-brain barrier, which may result in spread of disease along the cortical sulci, perivascular spaces and the cisterns around the base of the brain . Dural involvement is less frequent and shows diffuse dural thickening or focal dural masses with homogeneous enhancement (Fig. 4A).
Cranial nerve involvement can be seen isolated or in association with leptomeningeal disease. Imaging findings and clinical symptoms can be conflicting, with cranial nerve deficits not being positive on imaging or with clinically silent positive imaging findings . Sarcoidosis can involve the optic nerve and sheath, this being the second most commonly affected cranial nerve after the facial nerve. Patients can present with decreased vision or vision loss, which is sometimes rapid and painful . MRI reveals enhancement, thickening or atrophy and increased T2-weighted signal of the optic nerve (Fig. 5 A-D), as well as thickening, nodularity and enhancement of the nerve sheath (“tram-track sign”). The abnormal signal and enhancement of the nerve can extend from the head of the nerve intracranially to the chiasm (Fig. 6), optic tracts and optic radiations . The findings are not specific and the differentiation from neoplastic or chronic inflammatory changes cannot rely on imaging alone (patient inFig. 5).
Involvement of the sinonasal cavities is rare and the radiological manifestations comprise nodular lesions of the nasal septum and inferior turbinates, mucosal thickening and partial or total opacification of the paranasal sinuses, sometimes with associated osteosclerosis (Fig. 7) . Osseous involvement of sarcoidosis is seen in approximately 13% of patients with sarcoidosis, with the skull rarely being involved . Lesions are most commonly lytic (Fig. 9A-B), but may appear as mixed or sclerotic on CT. There may be associated soft-tissue component . Patients with neurosarcoidosis may also rarely present with cerebrovascular manifestations such as parenchymal or subarachnoid hemorrhage and stroke. Involvement of the larger venous sinuses has also been reported .
Optimal therapy can achieve clinical remission with variable improvement in imaging findings (Fig. 9C-F).
Langerhans cell histiocytosis
The histiocytosis are rare disorders characterized by the accumulation of macrophage, dendritic cell, or monocyte-derived cells in various tissues and organs . Langerhans cell histiocytosis (LCH) is the most common histiocytic disorder and is characterized by granulomatous lesions comprising langerin-positive (CD207+) histiocytes . LCH includes a broad spectrum of clinical manifestations in children and adults, ranging from self-healing to life-threatening disseminated disease. The diagnosis of LCH is based on clinical and radiological findings in combination with histopathological analyses identifying tissue infiltration by histiocytes (Fig. 12 and 13). LCH may affect any organ of the body.
In children, the lungs are affected in 15% of the patients, while pituitary gland involvement is more frequently seen in 25% of cases and the CNS involvement, excluding the pituitary, is extremely seldom (2-4%) . In adults, lung involvement is more frequent than in children. Lung LCH of the adult is strongly associated with smoking and occurs predominantly in men.
· Thoracic involvement:
On HRCT of the lung the appearance of LCH varies with the stage of the disease. In early cases small scattered lung nodules with soft tissue attenuationare seen. Over the time these have the tendency to cavitatewith formation of thick-walled lung cysts which tend to have irregular, bizarre shapes (Fig. 10, 11). Thus, a combination of nodules, cavitary nodules and cysts can be seen. Late disease may present with cysts that nearly replace the entire lung parenchyma, necessitating lung transplantation. These abnormalities present an upper lobe predominance with relative sparing of the lung bases and costophrenic angles. As with any cystic lung disease, the initial presentation may be due to the development of a pneumothorax.
· Intracranial involvement:
Intracranial LCH lesions affect the skull, meninges, hypothalamic-pituitary region and are sometimes associated with neurodegeneration.
The hypothalamic-pituitary axis is, by far, the most frequently involved intracranial region in LCH with the resulting clinical manifestation of diabetes insipidus. The imaging findings include an enhancing thickening of the pituitary stalk, greater than 3 mm, accompanied by the “loss of bright spot” (Fig. 12B) . Also, atrophy (Fig. 12A-C) and threadlike narrowing of the infundibulum with a maximum width less than 1 mm can be seen. The LCH-associated pineal gland abnormalities comprise solid masses or cystic lesions . Space occupying tumorous lesions can occur rarely in the meninges, choroid plexus and in the brain parenchyma .
Cranial-facial involvement with osseous lesions in the bones of the orbits and calvaria is a classical presentation of LCH. They present as punched out osteolytic lesion with scalloped edges and soft tissue involvement (Fig.14). They produce full thickness bone destruction. It was also shown that opacification in the paranasal sinuses or mastoids (Fig. 15) was more frequent in LCH patients than in controls .
Another presentation of CNS LCH is a combination of pathologic changes in the cerebellum, basal ganglia and/or pons with characteristic MRI patterns “radiological neurodegeneration” . Some patients present with subtle hyperintensity of the dentate nucleus on T1-weighted images (Fig.12 D and Fig. 16A). The dentate nucleus develops a hyperintensity on T2 weighted images, with subsequent extension of this T2 weighted hyperintensity to the perinuclear white matter over months and years [9, 11]. In the basal ganglia the abnormalities consist of hyperintense signals on T1-weighted images, usually involving globus pallidum (Fig. 12E, Fig. 16B-C). The increase of signal intensity abnormalities in the cerebellum and basal ganglia does not correlate with neurologic deterioration .
Lymphangioleiomyomatosis (LAM) is a rare multisystem disease predominantly affecting women of childbearing age. Most LAMs are sporadic (S-LAM), but they can also occur in association with tuberous sclerosis complex (TSC-LAM), an autosomal dominant disorder with variable penetrance associated with neurologic, renal and cutaneous manifestations. LAM predominantly affects the lungs, but can also occur along the axial lymphatic system, including the lymph nodes in the mediastinum, retroperitoneum, pelvic cavity and thoracic duct .
· Thoracic involvement:
Characteristic HRCT features of LAM include the presence of multiple, bilateral, round, well-defined, relatively uniform, thin-walled cysts in a diffuse distribution(Fig. 17 A-C). The intervening lung parenchyma often appears normal on HRCT. Other associated features that can be seen on HRCT in some patients with LAM include the presence of: chylous pleural effusion, pneumothorax (Fig.17A, C), ground-glass opacity suggestive of chylous congestion, or multiple tiny nodules characteristic of multifocal micronodular pneumocyte hyperplasia (MMPH, in patients with TSC-LAM, Fig. 19 A-Band Fig. 20) . Another characteristic finding in TSC-LAM is the presence of angiomyolipomas (AML) of the kidney. The diagnosis of AML can usually be made on the basis of the presence of fat in the tumors (Fig. 17D) .
· Intracranial involvement:
Because of the relatively high frequency of TSC-LAM, routine brain screening with MRI and computed tomography is performed for evidence of TSC in patients with LAM. Patients with documented TSC manifests within the brain with cortical or subcortical tubers, subependymal nodules, subependymal giant cell astrocytoma, cortical dysplasia and white matter abnormalities.
Cortical tubers are benign hamartomas in the cerebral cortex, typically appearing on MRI as well-circumscribed or voluminous areas of low signal intensity on T1-weighted and high signal intensity on T2-weighted sequences (Fig. 18B-Cand Fig. 19C-D). In children, initially the signal intensities are high on T1-weighted and low on T2-weighted sequences and they change over the time because of the progressive myelination. Subependymal nodules (SEN)are hamartomatous lesions lining the ventricular walls that can degenerate into subependymal giant cell astrocytomas (SEGA). They can show calcifications on CT (Fig. 18 A-B). Due to the compressive effect, SEGAs localized in the region of foramen Monro can produce ventricular obstruction and hydrocephalus. The white matter abnormalities can reveal radial migration lines (radial bands) stretching from the periventricular white matter to the subcortical region (Fig. 18C-D) . Extremely seldom, in patients with LAM extraaxial tumor masses with morphological characteristics of meningiomas are found (Fig. 18E) .
Systemic vasculitides are idiopathic diseases causing an inflammatory injury to the vessel walls with vessel destruction. Their classification is based on the size of vessels principally involved (large, medium and small). Three main immunological mechanisms of vessel damage have been identified: deposition of immune complexes, antibody-mediated and/or cell-mediated immunity and granulomatous reaction. In addition, vasculitis may be associated with systemic connective tissue disorders, like lupus vasculitis.
· Thoracic involvement:
Pulmonary involvement can be identified in all systemic vasculitides, however it tends to include small vessels inflammatory processes, Behcet disease or lupus vasculitis. The abnormalities can affect any anatomical or functional component of the lung: vessels (pulmonary and/or systemic), parenchyma, airways (trachea and bronchi) and pleura . Lung involvement is suggested by a pattern of diffuse or focal ground glass opacities reflecting pneumonitis or alveolar hemorrhage (Fig. 27), nodules or masses with or without cavitation (Fig. 24B-D), parenchymal consolidations (Fig. 21), tracheal or bronchial abnormalities (wall thickening, Fig. 21B, and stenosis), vascular abnormalities (aneurysms, wall thickening, stenosis and inflammation), reticulonodular pattern (Fig. 26A) and pleural disease (Fig. 21, Fig. 24, Fig. 28) .
· Intracranial involvement:
The clinical course of cerebral vasculitis ranges from fulminant to indolent and may be marked by fluctuations in clinical sign. While some patients present with normal cerebral MRI scan, most of them show changes such as multiple small intraparenchymal (gray or white matter) lesions consistent with ischemic stroke (Fig. 22, Fig. 23A-D, Fig. 25 A-D). These lesions do not have a periventricular predilection. Small petechial hemorrhages (Fig. 25E-G) or larger areas of hemorrhage or infarction(Fig. 28E-F) may also be found. Some patients may have enhancement of the meninges or of the small penetrating arteries. The cerebral arteries may demonstrate a beaded appearance with variable degrees of stenosis or occlusion(Fig. 23G-H) and contrast enhancement of the vessel walls (Fig. 23E-F). Because most inflammatory vasculitides affect small to medium caliber arteries, the results of MR angiography of the brain may often also be normal (Fig. 25H) [17, 18]. In younger patients under the age of 45 years, lesions demonstrated by MRI are likely to represent changes associated with vasculitis, especially if the cortex or the corticomedullary junction is involved and if the number of small focal hyperintense lesions is high (Fig. 26 B-C) .