Mediastinal Disorders

10 Mediastinal Disorders


Mediastinal Cysts


Definition


image Epidemiology


Most common mediastinal cysts image Developmental anomalies of the embryonal foregut image Isolated cystic lesions image Forms include pericardial cysts, thymic cysts, bronchogenic cysts, esophageal duplication cysts, and neuroenteric cysts.


image Etiology, pathophysiology, pathogenesis


Bronchogenic cysts arise from the ventral foregut, enteric cysts from the dorsal foregut image Bronchogenic cysts contain respiratory epithelium, smooth muscle, and cartilage; enteric cysts contain squamous and gastrointestinal epithelium, smooth muscle, and nerve plexus.


Imaging Signs


image Modality of choice


MRI is equivalent to CT.


image CT and MRI findings


Smoothly demarcated, thin-walled, cystic, spherical or ellipsoid mass showing no enhancement with contrast image Cysts with serous contents (most common) exhibit water-equivalent density (most common in pericardial cysts), those with other contents (mucus, calcium milk, blood) show higher density image Bronchogenic cysts image Cysts rarely communicate with the tracheobronchial or esophageal lumen (air–fluid level) image On MRI, cysts show variable signal behavior depending on the contents, typically appearing markedly hyperintense on T2-weighted sequences and hypointense or hyperintense on T1-weighted sequences image Bronchogenic cysts are usually subcarinal and paratracheal (> 50% on the right side, 15% in the pulmonary region) image Esophageal duplication cysts usually occur in a distal paraesophageal location (more often on the right than left) and are rarely intramural image Neuroenteric cysts occur in the mediastinum superior to the carina and in 50% of cases are associated with spinal anomalies.


image Pathognomonic findings


Water-equivalent density and signal intensity image No enhancement image Typical location image Neuroenteric cysts are associated with spinal anomalies.


Clinical Aspects


image Typical presentation


One-third are asymptomatic incidental findings image Two-thirds are symptomatic (causing airway or esophageal obstruction) and usually already manifest in infancy.


image Therapeutic options


Complete surgical resection is usually indicated even for asymptomatic cysts image Pericardial cysts usually require no treatment.


image Course and prognosis


Prognosis is excellent following complete excision.


image What does the clinician want to know?


Diagnosis and differential diagnosis image Location and extent (resection) image Impairment of adjacent structures.


image


Fig. 10.1 Pericardial cyst in a 52-year-old woman (incidental finding). The plain chest radiograph (a) shows a circumscribed convex shadow in the right cardiophrenic angle with a cardiac silhouette sign. The shape and location suggest a pericardial cyst. This was confirmed on MRI, where the lesion exhibited signal intensity typical of a cyst (b).


image


Fig. 10.2 MR image of a bronchogenic cyst. The cyst has a typical spherical shape, is smoothly demarcated, thin-walled, and exhibits homogeneous, fluid-equivalent density.


Differential Diagnosis

























Thymus cyst


– Location: upper anterior mediastinum


Pericardial cyst


– Pericardial contact


– Usually in the cardiophrenic angle (right side in 70% of cases, left in 22%)


– Invariably water equivalent


Lymphangioma


– Occurs in infancy


– Multicystic or septate


– With axial or cervical ramifications


Meningocele


– Paravertebral cystic formation isodense and isoin-tense to CSF and continuous with the dural sac


– Occasionally with widening of the neural foramen


Tumor cysts


– Thymic and germ cell tumors: solid tumor components predominate


Pancreatic pseudocyst


– Signs of a complicated cyst (irregularity, septation, marginal enhancement, reaction in adjacent tissue)


– History of pancreatitis


image


image


Fig. 10.3 Thymic cyst.


a The plain chest radiograph shows a widening of the mediastinal shadow on the right by a large, smoothly demarcated paracardiac mass with a shallow convex lateral margin obscuring the right margin of the heart (silhouette sign).


b CT (above) and MRI (below) show liquid cystic findings. The thymic cyst was confirmed intraoperatively. The size and cranial location are largely inconsistent with a pericardial cyst.


Tips and Pitfalls


Can be misdiagnosed as a solid mass image Complicated cysts are not clearly distinguishable from cystic tumors.


Selected References

Jeung MY et al. Imaging of cystic masses of the mediastinum. Radiographics 2002; 22: 79–93


Kim JH, Goo JM, Lee HJ. Cystic tumors in the anterior mediastinum: radiologic-pathological correlation. J Comput Assist Tomogr 2003; 27: 714–723


Strollo DC, Rosado-de-Christensom ML, Jett JR. Primary mediastinal tumors: Part 1 Tumors of the anterior mediastinum. Part 2 Tumors of the middle and posterior mediastinum. Chest 1997; 112: 511–522, 1344–1357


Takeda S, Miyoshi S, Minami M. Clinical spectrum of mediastinal cysts. Chest 2003; 124: 125–132


Retrosternal Intrathoracic Goiter


Definition


image Epidemiology


Goiter occurs on average in about 5% of the population (in Germany), about 20% of these have an intrathoracic component image Three times as common in women than in men.


image Etiology, pathophysiology, pathogenesis


Primary goiter occurs with an accessory intrathoracic thyroid (with thoracic vascular supply) image Secondary goiter develops as a ramification of a cervical goiter (with cervical vascular supply) image Develops in response to thyroid-stimulating hormone in iodine deficiency or thyroid insufficiency.


Imaging Signs


image Modality of choice


Radiographs, CT, nuclear medicine.


image Radiographic findings


Smoothly demarcated space-occupying lesion in the anterior upper mediastinum that moves when the patient swallows and leads to tracheal shift and/or compression image Calcifications occur in 25% of cases.


image CT findings


Smoothly demarcated mass appearing hyperdense on plain scans due to iodine (70–120 HU) and located in the upper mediastinum (75% anterior to the trachea, 25% posterior) image Tracheal shift (occasionally with compression) image Calcifications and colloid cysts are common findings image Enhances markedly on contrast-enhanced image Contrast-enhanced CT scans should be performed only after nuclear medicine studies.


image Nuclear medicine


Nuclide uptake (iodine-123) equivalent to thyroid tissue.


image Pathognomonic findings


Mass in the anterior upper mediastinum continuous with the thyroid and displacing and/or compressing the trachea and/or esophagus.


Clinical Aspects


image Typical presentation


Usually asymptomatic where only mild hypothyroidism is present (variable thyroid function is normal; thyroid function tests are indicated) image Stridor and/or dyspnea, dysphagia, and dysphonia depending on size and location.


image Therapeutic options


Surgical resection is indicated for large symptomatic goiters and where malignancy is suspected image Thyroid function tests are invariably indicated.


image Course and prognosis


Prognosis is good for benign goiters image Prognosis for malignant goiters depends on the histology.


image What does the clinician want to know?


Confirmation of tentative diagnosis image Determine whether findings appear malignant image Thyroid function.


image


Fig. 10.4 Retrosternal goiter in a 66-year-old woman. The plain chest radiograph shows a space-occupying lesion at the level of the thoracic inlet with coarse patchy calcifications and a right convex tracheal shift. Other findings include a fatty mass in the right paracardiac region.


Differential Diagnosis



















Thymic tumor


– Located farther caudally and not continuous with the thyroid


– Lesser density and enhancement on CT


Teratoma


– Located farther caudally and not continuous with the thyroid


– Lesser density and enhancement on CT


– Fatty components


Lymphoma


– No calcifications initially


– Multinodular


– Lesser density and enhancement on CT


Castleman disease


– Strong contrast enhancement similar to goiter


– Not continuous with the thyroid


– Multinodular and multilocular


Tips and Pitfalls


Difficulties with differential diagnosis are to be expected only with the primary form.


Selected References

Duwe BV, Sterman DH, Musani AI. Tumors of the mediastinum. Chest 2005; 128: 2893–2909


Strollo DC, Rosado-de-Christenson ML, Jett JR. Primary mediastinal tumors: Part 1 Tumors of the anterior mediastinum. Chest 1997; 112: 511


image


Fig. 10.5 Retrosternal goiter in a 76-year-old woman. The axial (b) and coronal CT-images show a severe cervical goiter with regressive changes (cystic necrotic components and calcifications). The goiter extends far into the anterior upper mediastinum, significantly displacing the carotid arteries and brachiocephalic veins. The trachea shows a right convex shift with only slight compression. The cardinal diagnostic criteria are the continuity of the mediastinal mass with the thyroid and its equivalent texture.


Thymic Tumors


Definition


image Epidemiology


Account for about 20% of primary mediastinal tumors image Most common mass in the anterior mediastinum aside from teratoma, lymphoma, and goiter image Occurs exclusively in the anterior mediastinum anterior to the heart and great vessels image Occurs at age 40–60 image Often associated with other clinical pictures and findings (especially myasthenia gravis, red cell aplasia, hypogammaglobulinemia).


image Etiology, pathophysiology, pathogenesis


The classification of thymomas is based on the predominant cell type, epithelial or lymphocytic image Encapsulated and invasive lymphomas are histologically identical image Other thymic tumors and tumorlike processes include thymic cyst, thymic lipoma, thymic carcinoma, and thymic carcinoid.


Imaging Signs


image Modality of choice


CT is preferable to MRI.


image CT findings


Thymoma: Solid round or oval smoothly demarcated mass in the anterior upper mediastinum (usually < 10 cm) image Necrotic, cystic, hemorrhagic components image Calcifications in 25% (not a criterion of malignancy) image 35% of thymomas show locally invasive growth—pericardial thickening, vascular encasement, pleural metastases image Invasive forms of thymoma are indistinguishable from thymic carcinoma, thymic carcinoid, or malignant germ cell tumor.


Thymic carcinoma: Usually > 10 cm image Irregular image Ill-defined margin image Signs of image Heterogeneous enhancement image Involvement of mediastinal lymph nodes in 40% of cases image Metastases (lung, liver) in 30%.


Thymic cyst: Thin-walled image Usually a solitary finding.


Thymic lipoma: Sharply demarcated image Fat-equivalent density.


Thymic carcinoid: Resembles a thymoma image Involvement of mediastinal lymph nodes or metastases in 20–30% of cases.


image MRI findings


Thymoma: Isointense to muscle on T1-weighted sequences, cystic components are hypointense image Hyperintense on T2-weighted sequences, cystic components are markedly hyperintense.


Thymic carcinoma: Heterogeneous signal behavior and enhancement.


Thymic cyst: Hypointense on T1-weighted sequences image Markedly hyperintense on T2-weighted sequences.


image Pathognomonic findings


Round or oval lobulated mass in the anterior upper mediastinum < 10 cm.


image


Fig. 10.6 Thymoma in a 43-year-old man. The plain chest radiograph shows a large mass in the right anterior mediastinum. On the lateral film (b) the tumor shows a convex partial calcification. Slightly high-riding right diaphragmatic crus. Histological examination revealed a thymoma with no evidence of malignancy.


Clinical Aspects


image Typical presentation


Thymoma: Myasthenia gravis (diplopia, ptosis, weakness) in 50% of cases.


Thymic carcinoma: Chest pain image Weight loss image Paraneoplastic syndrome in rare ing syndrome image Multiple endocrine neoplasia (MEN) 1 syndrome.


Thymic cyst and thymic lipoma: Asymptomatic incidental findings.


image Therapeutic options


Resection.


image Course and prognosis


Thymoma: Prognosis is good where the capsule is intact, moderate for invasive cases image Thymic carcinoma: Poor prognosis.


image What does the clinician want to know?


Localization and extent (for biopsy and/or resection) image Involvement of adjacent structures.


Differential Diagnosis
















Retrosternal goiter


– Continuous with the thyroid


– Higher density than muscle on CT


– Regressive changes are common


Lymphoma


– Thymic involvement in the setting of a generalized lymphoma (usually Hodgkin disease)


Teratoma or germ cell tumors


– Similar cross-sectional morphology


– Clinical findings and laboratory results are required to distinguish these disease entities


Tips and Pitfalls


Thymic carcinoma is indistinguishable from invasive thymoma on imaging studies image Complete resection is required to distinguish between the two conditions.


Selected References

Duwe BV, Sterman DH, Musani AI. Tumors of the mediastinum. Chest 2005; 128: 2893–2909


Nishino M et al. Thymus—a comprehensive review. Radiographics 2006; 26: 335–348


Strollo DC, Rosado-de-Christenson ML, Jett JR. Primary mediastinal tumors: Part 2 Tumors of the middle and posterior mediastinum. Chest 1997; 112: 1344–1357


Germ Cell Tumors


Definition


image Epidemiology


Germ cell tumors account for about 15% of primary mediastinal tumors image Predilection for the anterior mediastinum, often adjacent to the thymus image Predilection for young men image Teratoma is the most common germ cell tumor of the mediastinum, seminoma the most common malignant form.


image Etiology, pathophysiology, pathogenesis


The germ cell tumors include teratomas (usually benign, rarely teratocarcinomas), seminomas, and nonseminomatous germ cell tumors (embryonal carcinoma, yolk sac tumors, choriocarcinoma, and mixed tumors).


Imaging Signs


image Modality of choice


CT, MRI.


image CT and MRI findings


Seminoma: Large solid, usually lobulated mass of homogeneous density; cystic or necrotic areas are rare


Teratomas: Mature teratomas are the only germ cell tumors to exhibit typical findings (see below)


Teratocarcinoma: Irregularly demarcated tumor with inhomogeneous contrast enhancement, calcifications, necrosis, and signs of infiltration.


image Pathognomonic findings


Mature teratomas are the only germ cell tumors to exhibit typical findings on imaging studies—they are well demarcated round or lobulated tumors with cysts, calcifications or ossifications, and fatty tissue (50% of cases) image Primordia of tooth and/or bone or fat–fluid levels are pathognomonic findings.


Clinical Aspects


image Typical presentation


Asymptomatic incidental finding or symptomatic lesion image Symptomatic tumors (cough, pain, dyspnea, fever) suggest malignancy image AFP is elevated in embryonal image HCG is elevated in choriocarcinoma image Pure seminomas do not show raised AFP and only occasionally raised HCG (10% of cases). Exclude a primary testicular tumor.


image Therapeutic options


Mature teratomas: Resection image Seminomas: Combined radiation therapy and chemotherapy image Nonseminomatous germ cell tumors: Chemotherapy and resection.


image Course and prognosis


Mature teratomas: Excellent prognosis image Pure seminomas: Very good prognosis image Mixed tumors: Variable prognosis.


image What does the clinician want to know?


Localization and extent (for biopsy and/or resection) image Involvement of adjacent structures.


image


Fig. 10.7 Mature teratoma in a 37-year-old woman (incidental finding).


a The plain chest radiograph shows a sharply demarcated convex mass in the aortopulmonary window.


b CT also shows a smoothly demarcated lesion with focal mural calcifications and components isodense to fat and soft tissue.


image


Fig. 10.8 Extragonadal germ cell tumor in a 26-year-old man with chest pain.


a The plain chest radiograph shows an abnormally widened anterior upper mediastinum.


b CT visualizes the tumor as a lobular mass with inhomogeneous density and liquid components suggestive of necrosis.


Differential Diagnosis
















Lymphoma


– Homogeneous solid mass


– Multilocular


– Often indistinguishable from a seminoma


Thymoma or thymic tumor


– Indistinguishable from malignant germ cell tumors


Retrosternal goiter


– Continuous with the thyroid


– Higher density than muscle on CT


Tips and Pitfalls


Except for mature teratomas, it is impossible to determine whether findings are malignant.


Selected References

Duwe BV, Sterman DH, Musani AI. Tumors of the mediastinum. Chest 2005; 128: 2893–2909


Kim JH, Goo JM, Lee HJ. Cystic tumors in the anterior mediastinum: radiologic-pathological correlation. J Comput Assist Tomogr 2003; 27: 714–723


Moeller KH, Rosado-de-Christenson ML, Templeton DA. Mediastinal mature teratoma: imaging features. AJR Am J Roentgenol 1997; 169: 985–990


Strollo DC, Rosado-de-Christenson ML, Jett JR. Primary mediastinal tumors: Part 1 Tumors of the anterior mediastinum. Chest 1997; 112: 511


Neurogenic Tumors


Definition


image Epidemiology


Account for 10–20% of mediastinal masses image 90% occur in the posterior mediastinum image Usually benign (80%).


image Etiology, pathophysiology, pathogenesis


Several forms are differentiated: Peripheral nerve sheath tumors (schwannomas or neurilemmomas, neurofibromas, malignant nerve sheath tumors; usually in adults) image Tumors of the sympathetic ganglia (ganglioneuromas, ganglioneuroblastomas, neuroblastomas; usually in children under 10) image Tumors of the para-sympathetic ganglia (very rare).


Imaging Signs


image Modality of choice


CT and MRI are indicated to evaluate intraspinal findings image MIBG imaging in neuroblastoma.


image CT findings


Schwannoma and neurofibroma: Paravertebral, smoothly demarcated round or lobulated mass isodense to soft tissue extending over one to two intercostal spaces image Homogeneous or heterogeneous density image Homogeneous, heterogeneous, or marginal enhancement image In 50% of cases there is compressive excavation of the vertebrae and or ribs image Widening of the neural foramen occurs with hourglass tumors (10%) image Plexiform neurofibroma is a variant.


Ganglioneuroma and ganglioneuroblastoma: Tumor tends to be long, extending over three to five segments with broad anterolateral contact with the spine image Homogeneous or heterogeneous density (stippled calcifications may occur) image Enhances moderately with contrast image Signs of malignancy include size > 5 cm, heterogeneity, local invasiveness (mediastinum or chest wall), hematogenous metastases (lung).


image MRI findings


Schwannoma and neurofibroma: Morphologic criteria as on CT image Low to intermediate signal intensity on T1-weighted sequences, intermediate to high signal intensity on T2-weighted sequences.


Ganglioneuroma and ganglioneuroblastoma: Heterogeneous signal intensity on all sequences.


image Pathognomonic findings


Smoothly demarcated round or lobulated tumors in a typical paravertebral location with compressive erosion of bone image Multiple neurogenic tumors and plexi-form neurofibromas are pathognomonic for neurofibromatosis.


image


Fig. 10.9 Neurilemoma in a 48-year-old man. The plain chest radiographs show only a spherical, smoothly demarcated paravertebral mass of soft tissue density in the posterior lower mediastinum. Even without widening of the intervertebral foramen, the lesion is most likely a neurogenic tumor because of its location. The lesion was confirmed intraoperatively as a neurilemoma.


image


image


Fig. 10.10 Neurofibroma in a 38-year-old woman.


a    The plain chest radiograph shows bilateral abnormal widening of the upper mediastinum primarily on the left side involving the thoracic inlet. A second tumor of soft tissue density is visualized laterally along the ribs in the left upper lung field. A local density is also visible projected on the right hilum.


b– e The CT images show the lesion in each case to be a smoothly demarcated extrapulmonary tumor homogeneously iso-dense to soft tissue without any bony destruction. Local widening of the intervertebral foramen was demonstrated only at the level of the thoracic inlet (not shown).


Clinical Aspects


image Typical presentation


The majority of benign tumors are asymptomatic image The majority of malignant tumors are symptomatic (pain, paresthesias, neurologic deficits) image A metabolically active neuroblastoma or ganglioneuroblastoma produces catecholamines and intestinal peptides that can cause hypertension, flush symptoms, and diarrhea.


image Therapeutic options


Radical surgical excision image Chemotherapy and resection are indicated for neuroblastoma and ganglioneuroblastoma.


image Course and prognosis


Prognosis is good for benign tumors that are excised completely image Local recurrence is common following incomplete resection or in neurofibromatosis image The prognosis for malignant tumors depends on the initial findings and the opportunity for radical treatment but on the whole is quite unfavorable.


image What does the clinician want to know?


Involvement of the spinal canal image Determine whether findings appear malignant (local invasiveness, metastases) image Staging in neuroblastoma and ganglioneuroblastoma:






















Stage I:


Ipsilateral, circumscribed, noninvasive


Stage II:


Locally invasive, does not cross the midline, no lymph node metastases


Stage III:

Crosses the midline, bilateral regional lymph node metastases

Stage IV:


Extensive metastases


Stage IVS:


Stage I or II tumors with metastases limited to the liver, skin, and/or bone marrow


Differential Diagnosis










Lateral thoracic meningocele


– Isodense and isointense to CSF

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Feb 28, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Mediastinal Disorders

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