Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses


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Variants and other difficult diagnoses

How often have you been confronted with an image on a thoracic CT exam where you knew it didn't look 'normal', but you weren't sure whether it was 'abnormal' either? And if it is abnormal, is there a specific diagnosis you should be able to make directly off the images? Pearls and Pitfalls in Thoracic Imaging is your one-stop resource to answer questions such as: Is this a normal variant or a disease-related abnormality? Are these findings specific for an uncommon disease and if so what is the diagnosis? Is this set of findings strongly suggestive of a diagnosis?

Which additional imaging test will allow me to be confident in that diagnosis? Could the 'abnormality' be due to an artifact mimicking disease? Duplication cysts are uncommon lesions lined by gastrointestinal tract mucosa and generally asymptomatic. However, if they contain gastric or pancreatic mucosa, there is the added risk of haemorrhage or rupture of the cyst from mucosal secretions.

The majority of them are detected adjacent to or within the oesophageal wall Fig.

Most pericardial cysts are unilocular and commonly located in the right cardiophrenic space Fig. However, they may occur anywhere in relation to the pericardium.

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Congenital cysts derive from remnants of the thymopharyngeal duct, they are typically unilocular and contain clear fluid Fig. In contrast, acquired thymic cysts are much more common, tend to be multilocular Fig. Lymphangioma is a rare benign lesion of lymphatic origin that represents 0.

Pancreatic pseudocyst can extend into the mediastinum via the oesophageal or aortic hiatus. CT shows a thin-walled, fluid-containing cyst within the posterior mediastinum which may be in continuity with the intrapancreatic or peripancreatic fluid collections Fig.

Mediastinal goitre generally represents direct contiguous growth of a goitre into the anterior or superior mediastinum. Typical features of mediastinal goitres are encapsulated and lobulated mass with inhomogeneous appearance with cystic areas, calcifications and marked contrast enhancement. An intrathoracic thyroid mass developing from heterotopic thyroid tissue without any connection to the thyroid in the neck is extremely rare Fig.

The presence of ill-defined margins, invasion of adjacent structures and nearby lymph node enlargement suggests the diagnosis of thyroid cancer [ 20 ] Fig. Thymic hyperplasia can be divided into two distinct histological types [ 13 , 14 ]. True thymic hyperplasia is defined as enlargement of the thymus, which generally retains its normal shape.

This disease entity is observed when a patient is recovering from some recent stress such as chemotherapy, corticosteroid therapy, irradiation or thermal burns. Thymic lymphoid follicular hyperplasia of the thymus refers to the presence of an increased number of lymphoid follicles. It is important for radiologists to be able to distinguish thymic hyperplasia from neoplasm. Diffuse symmetric enlargement of the gland, a smooth contour and normal vessels are the key morphological features of hyperplasia, whereas neoplasm tends to manifest as a focal mass with nodular contour and necrotic or calcified foci.

Detecting fat in the thymus is particularly relevant in these situations. According to Takahashi et al. Thymic hyperplasia reveals a relative signal loss on opposed-phase chemical-shift MRI that it is different from no significant signal change between in-phase and opposed-phase chemical-shift MR images in patients with malignancy Fig. In contrast to histological classification, the stage of thymoma has clinical implications and it is a useful tool for management decisions.

The Masaoka staging system is one of the two factors, including completeness of surgical resection, that most strongly correlates with prognosis of thymomas [ 23 ]. The role of imaging is to initially diagnose and properly stage thymoma, with emphasis on the detection of local invasion and distant spread of disease. On CT scans, thymomas usually appear as homogeneous solid masses with soft-tissue attenuation and well-demarcated borders, located anywhere from the thoracic inlet to the cardiophrenic angle. Thymomas may be oval, round or lobulated and when they are large, cystic or necrotic degeneration may be shown Fig.

Calcification may be present in the capsule or throughout the mass.

A diagnostic approach to the mediastinal masses | SpringerLink

Certain findings, such as encasement of mediastinal structures, infiltration of fat planes, irregular interface between the mass and lung parenchyma, and direct signs of vascular involvement are highly suggestive of invasion Fig. Thymoma rarely presents with metastatic lymphadenopathy, metastatic pulmonary nodules or pleural effusion. At MRI, thymomas commonly appear as homogeneous or heterogeneous masses with low to intermediate signal intensity on T1-weighted images and with high signal intensity on T2-weighted images Fig. MRI can prove useful in identifying the nodular wall thickening detected in cystic thymomas, absent from congenital cysts [ 22 ].

Table 1 WHO classification for thymoma. Lymphocytes are more numerous than in the type A component, but may be less numerous than in B1 thymomas B1 lymphocyte-rich thymoma; lymphocytic thymoma; organoid thymoma; predominantly cortical thymoma Epithelial cells with a histological appearance practically indistinguishable from the normal thymus, composed predominantly of areas resembling cortex with epithelial cells scattered in a prominent population of immature lymphocytes B2 cortical thymoma Tumour cells closely resembling the predominant epithelial cells of the normal thymic cortex.

A background population of immature T cells is always present and usually outnumbers the neoplastic epithelial cells B3 epithelial thymoma; squamoid thymoma Medium—sized round or polygonal cells with slight atypia. From Travis et al. Table 2 Masaoka-Koga staging system of thymoma. Stage Description I Macroscopically and microscopically encapsulated tumour IIa Microscopic invasion through the capsule IIb Macroscopic invasion into surrounding fatty tissue III Invasion into a neighbouring organ such as the pericardium, great vessels or lung IVa Pleural or pericardial dissemination IVb Lymphatic-haematogenous metastases.

Lymphoproliferative disorders. Primary mediastinal lymphoma usually occurs in the anterior mediastinum. Lymphomas are the most common cause of masses in the paediatric mediastinum [ 18 ]. Hodgkin lymphoma Fig. Pleural and pericardial effusions are often common features in all types of lymphoma. Hodgkin disease HD has a bimodal distribution of incidence peaking in young adulthood and again after the age of 50 years [ 4 ].

Most patients experience constitutional symptoms. Four subtypes of HD are described: nodular sclerosis by far the most common histological subtype Fig. Characteristic features on imaging are a homogeneous soft-tissue anterior mediastinal mass with mild to moderate contrast enhancement, irregular contours, surface lobulation, absence of vascular involvement, and high prevalence of associated mediastinal lymphadenopathy [ 3 ].

Cystic and necrotic changes can be identified. The two most common forms of mediastinal non-Hodgkin disease NHD include diffuse large B-cell lymphoma and T-cell lymphoblastic lymphoma.

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T-cell lymphoblastic lymphoma mainly occurs in children and adolescents. The most common CT appearance is a large mediastinal mass representing thymic and lymph node enlargement, which compresses the airway and cardiovascular structures Fig. Low attenuation areas reflecting necrosis are commonly seen. Primary mediastinal diffuse large B-cell lymphomas tend to occur in young to middle-aged adults with a mean age of 30 [ 5 ]. The tumours appear as a large, smooth or lobulated, anterior mediastinal mass in nearly all patients.

Primary mediastinal B-cell lymphoma recurs in the chest. Consequently, chest CT examination alone is sufficient for routine follow-up of these patients [ 28 ]. Teratoma is the most common mediastinal GCT [ 4 ]. They are composed of well-differentiated benign tissues with predominant ectodermal element. If a teratoma contains fetal tissue or neuroendocrine tissue, it is defined as immature and malignant with a poor prognosis. On CT, teratoma most commonly appears as a well-defined unilocular or multilocular cystic lesion containing fluid, soft tissue and fat attenuation Fig.

Calcifications may be focal, rim-like or, in rare cases, representative of teeth or bone. On MRI, teratomas typically demonstrate heterogeneous signal intensity, representing various internal elements. Fat-fluid levels within the lesion are virtually diagnostic of teratoma. Ruptured teratomas show an adjacent consolidation, atelectasis and pleural or pericardial effusion than do unruptured teratomas. The non-teratomatous germ cell tumours NTGCT are rare and malignant tumours which usually occur in young males and most frequently affect the anterosuperior mediastinum [ 29 ].

These tumours grow rapidly and develop large, bulky, ill-circumscribed masses with lobulated shape. At imaging, the tumours typically have homogenous appearance and show minimal contrast enhancement. Areas of degeneration due to haemorrhage and coagulation necrosis may be present Fig. Metastasis to lymph nodes and bone does occur. Non-seminomatous germ cell tumours include yolk sac tumours, endodermal sinus tumours, embryonal carcinomas, choriocarcinomas and mixed germ cell tumours, which present as large masses typically with marked heterogeneous attenuation. Invasion of adjacent structures and distant metastasis may occur.

Pleural and pericardial effusions are common.

Pearls and Pitfalls in Thoracic Imaging Variants and Other Difficult Diagnoses

They are usually solitary and encapsulated masses, but multiple schwannomas may be associated with neurofibromatosis type 2. Cystic changes and haemorrhage are more common in schwannomas than in neurofibromas. A sudden increase in the size of a previously stable neurofibroma and the presence of neurological symptoms suggests malignant transformation to malignant peripheral nerve sheath tumour.

Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses
Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses
Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses
Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses
Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses Pearls and Pitfalls in Thoracic Imaging: Variants and Other Difficult Diagnoses

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