Rosai Chapter 12 - Mediastinum Flashcards
Most common causes of superior vena cava syndrome in adults (2)
- Metastatic lung carcinoma
- Malignant lymphoma
Most common causes of superior vena cava syndrome in children (2)
- Malignant lymphoma
- Acute leukemia
Usually the result of traumatic perforation of the esophagus or descent of infection from within the neck through the “danger space” anterior to the prevertebral fascia
-Acute mediastinitis
Acute mediastinitis predominantly involves the:
Posterior mediastinum
Typical location of chronic mediastinitis
Anterior mediastinum, in front of the tracheal bifurcation
The organism most commonly identified in those cases of fibrosing mediastinitis for which a specific etiology can be determined
Histoplasma capsulatum (Histoplasmosis)
Characterized by coarse, keloid-like, collagen deposition that can invade the superior vena cava, resulting in SVC syndrome, and can also invade the pulmonary hilum, resulting in complete occlusion of hilar vessels
Fibrosing mediastinitis
Formed by the fusion of multiple disconnected lacunae
Pericardial sac
Congenital cyst that occur along the tracheobronchial tree
Bronchial cyst
Most common location of Bronchial cyst
Posterior to the carina
Probably arise from a persistence, in the wall of the foregut, of vacuoles that form during the solid tube stage of development
Esophageal cysts
Best evidence that a cyst in the location of the esophagus is of esophageal type
Presence of a definite double layer of smooth muscle in the wall
Symptomatic congenital cysts (2)
- Gastric cysts
- Gastroenteric cysts
Asymptomatic congenital cysts (3):
- Bronchial cysts
- Esophageal cysts
- Enteric cysts
Largest lymph vessel in humans
Thoracic duct
Most common pathologic change in mediastinal thyroid glands
Nodular hyperplasia
Major cell types of the thymus (2)
- Epithelial cells
- Lymphocytes
A major cell type of the thymus that is endodermally derived with a possible minor ectodermal contribution
Epithelial cells
A major cell type of the thymus that is bone marrow-derived
Lymphocytes
Normal location of B-cells in the thymus
- Thymic medulla
- Perivascular compartment
Most salient features of Thymic dysplasia (5)
- very small size (less than 5 grams)
- primitive appearing epithelium without segregation into cortical and medullary regions
- presence of tubules and rosettes
- absence of Hassall corpuscles
- almost total absence of lymphocytes
Diseases with accompanied Thymic dysplasia (3)
- X-linked or Autosomal recessive form of (S, A, R)
- Nezelof syndrome
- incomplete form of DiGeorge syndrome (dysplastic and located ectopically)
X-linked or Autosomal recessive forms of these diseases has an accompanied Thymic dysplasia (3)
- Severe combined immunodeficiency
- Ataxia-Telangiectasia
- related chromosomal instability syndromes
Main differential diagnosis of Thymic dysplasia
Acute Thymic involution
Best evidence against the diagnosis of primary thymic dysplasia
identification of well-formed hassall corpuscles in a thymus biopsy
UNILOCULAR / MULTILOCULAR
Thymic cysts:
Developmental origin arise from remnants of the 3rd branchial pouch-derived thymopharyngeal duct
Unilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
usually Small
Unilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
can be seen mostly in the Neck than in the mediastinum
Unilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
This cervical thymic cyst is elongated and can be found anywhere along a line extending from the angle of the mandible to the manubrium sternum
Unilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
Wall is thin and translucent
Unilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
Lacking inflammation
Unilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
Rarely has squamous lining
Unilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
Thymic tissue present in the wall
Unilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
Acquired process of reactive nature
Multilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
Always accompanied by inflammation and fibrosis
Multilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
Often has squamous lining
Multilocular
UNILOCULAR / MULTILOCULAR
Thymic cysts:
An acquired cystic dilation of medullary duct epithelium-derived structures, induced by an inflammatory reaction of the thymic parenchyma
Multilocular
Most commonly associated tumors with multilocular thymic cyst (2)
- Hodgkin lymphoma
- Seminoma
Ectopic thymic tissue in the skin of the neck
Branchio-oculo-facial syndrome
A term that should be restricted to neoplasms of thymic epithelial cells, independently of the presence of number of lymphocytes
Thymoma
Usual location of thymoma
Anterosuperior mediastinum
A patient with myasthenia is more likely to have a thymoma if (2):
- Male; and/or
- developing symptoms after the age of 50
Most accurate way to predict the likelihood of myasthenia in a patient with Thymoma
find Lymphoid follicles in the adjacent non-neoplastic thymic tissue, or, exceptionally, even in the thymoma itself
Features suggestive of organoid differentiation in Thymoma (5):
- perivascular spaces containing lymphocytes, proteinaceous fluid, RBCs, foamy macrophages, or fibrous tissue
- Rosettes without central lumens
- Glandlike formations within the tumor or, more often, in the tumor capsule
- True glandular structures
- Whorls suggestive of abortive Hassall corpuscle formation
Thymoma vs. Thymic carcinoid:
rosette-like structures with well-defined lumens
Thymic carcinoid
Important clue to the diagnosis of lymphocyte-rich (type B1) thymoma
find round, lighter foci of medullary differentiation
Most frequent aberration found in thymoma are located on:
chromosome 6 (6q25.2)
IHC with highest sensitivity for thymic carcinoma (2)
- MUC-1
- GLUT-1
IHC showing greater specificity in separating carcinoma from thymoma
CEA
IHCs that stain strongly with thymic carcinoma than thymoma (3)
- p53
- BCL-2
- p16
Most common recurrent mutations, occurring in about 30% of cases of thymic carcinoma
TP53
Main differential diagnosis of Basaloid carcinoma of Thymus
Thymic carcinoma with adenoid cystic carcinoma-like features
Most common histologic appearance of NUT (midline) carcinoma of the Thymus
a highly undifferentiated carcinoma with variably conspicuous foci of abrupt squamous differentiation
Two important factors for the new nomenclature of thymic tumors:
- Thymus is unique, can be viewed as two different organs
- Presence, as an expression of differentiation, of a non-neoplastic lymphocytic component in the tumors composed of functional thymic tissue
“Thymus is unique, can be viewed as two different organs”
-The active, functional gland of the (2)
- Fetus
- Infant
“Thymus is unique, can be viewed as two different organs”
-the inactive, “post mature” structure of:
-Adult life
Better differentiated tumors of thymus (2)
- Lymphocyte-rich
- predominantly cortical types
Two major types of thymoma are based on (2):
- cytological characteristics of neoplastic epithelial cells
- relative contribution of non-neoplastic immature T-lymphocytes typical of normal thymic cortex
Subdivision of type B thymomas is based on (2):
- proportional increase (in relation to the lymphocytes) of the neoplastic epithelial cells
- emergence of atypia of the neoplastic epithelial cells
Most reproducible features for identifying this extremely rare variant for which the term atypical type A thymoma has been proposed (2):
- Mitotic activity (more than or equal to 4/10 hpf)
- Necrosis
Only feature that predicted for higher tumor stage in a large retrospective cohort of type A and AB thymomas
necrosis
type AB / type B1 Thymoma:
-spindled / oval morphology
type AB
type AB / type B1 Thymoma:
-immunoreactivity for CD20 in epithelial tumor cells within lymphocyte-rich areas
type AB
type AB / type B1 Thymoma:
-presence of Hassall corpuscles
type B1
type B1 / type B2 Thymoma:
-absence of epithelial cell clusters
type B1
type B1 / type B2 Thymoma:
-presence of medullary islands
type B1
Micronodular / type AB thymoma:
-the lymphocytes are composed mainly of B-cells and mature T-cells
Micronodular thymoma
Micronodular / type AB thymoma:
-Negative staining for CD20
Micronodular Thymoma
Most important criterion for the cytologic recognition of a thymoma
-identification of a distinct population of epithelial cells admixed with lymphocytes, preferably confirmed by a positive immunostain for keratin
Primary treatment of Thymoma (2)
- en-bloc surgical excision
- complete thymectomy
Remains the single most important prognostic determinant, regardless of the system used, and applies equally to thymomas and thymic carcinoma
Stage
Directly related to the tumor stage and is also an important prognostic parameter
Completeness of excision
Main differential diagnosis for SETTLE
Synovial Sarcoma
SETTLE should be favored over Synovial sarcoma in the presence of (5):
- Stromal hyalinization
- Lower overall grade
- presence of glomeruloid glandular structures
- absence of intraglandular necrotic debris
- diffuse expression of HMW keratin
More significant predictors of outcome of thymic neuroendocrine tumors (3):
- Stage
- Resectability
- presence of paraneoplastic endocrinopathies
The presence of these features favor a diagnosis of Seminoma vs other thymic neoplasms (5):
- fibrous septa infiltrated by lymphocytes and plasma cells
- epithelioid granulomas
- numerous germinal centers
- large amounts of cytoplasmic glycogen
- an irregular, skein-like nucleolus
Accounts for the majority of germ cell tumors in children
Mature cystic teratoma
Second most common mediastinal germ cell tumor in children less than 15 years of age
Yolk sac tumor (Endodermal sinus tumor)
Only other type of mediastinal germ cell tumor showing trophoblastic differentiation reported in a 14-year-old boy 2 years after resection of a teratoma
Placental site trophoblastic tumor
Most common primary neoplasm of the middle portion of the mediastinum
Malignant Lymphoma
Older term for Lymphoblastic Lymphoma
Convoluted cell lymphoma
Other reasons for the frequent misdiagnosis of Primary mediastinal (Thymic) Large B-cell Lymphoma (5):
- perivascular collections of Lymphocytes (which may be misinterpreted as the perivascular spaces of thymoma)
- artifactual clearing of the cytoplasm induced by formalin fixation (not present in B5 or Zenker’s fixed material) simulating seminoma
- presence of a large number of reactive T-cells
- rosette-like formations mimicking Thymoma and Thymic carcinoma
- Entrapment of thymic epithelium
A diagnosis of large cell lymphoma should be favored in the presence of (4):
- Tumor cells with large, vesicular, irregularly-shaped nuclei (indented, kidney-shaped, polylobated)
- entrapment of intrathymic and perithymic fat
- invasion of blood vessel wall, pleura, or lung
- the fact that the fibrosis is manifested not only in the form of wide hyaline bands but also as a fine network that entraps individual cells
an integral membrane protein located in glycolipid-enriched membrane microdomains called lipid rafts
MAL
A distinct molecular marker for primary mediastinal (Thymic) large B-cell lymphoma
MAL
Primary diseases associated with Extramedullary hematopoiesis in most patients
- Hereditary spherocytosis
- Thalassemia
Two major categories of Neurogenic Tumors (2):
- tumors of the Sympathetic Nervous System
- tumors of Peripheral Nerve Sheath
Anterior boundary of the mediastinum
Sternum
Posterior boundary of the mediastinum
Spine
Superior boundary of the mediastinum
Thoracic inlet
Inferior boundary of the mediastinum
Diaphragm
Most common lesions in the Superior Mediastinum (4)
- Thymoma and Thymic cyst
- Malignant Lymphoma
- Thyroid lesions
- Parathyroid adenoma
Most common lesions in the Middle Mediastinum (3)
- Pericardial cyst
- Bronchial cyst
- Malignant Lymphoma
Most common locations of Thymoma and Thymic cyst in the mediastinum (2)
- Superior
- Anterior
Most common locations of Malignant Lymphoma in the mediastinum (3)
- Superior
- Anterior
- Middle
Most common locations of Thyroid lesions in the mediastinum (2)
- Superior
- Anterior
Most common locations of Parathyroid adenoma in the mediastinum (2)
- Superior
- Anterior
Most common locations of Paraganglioma in the mediastinum (2)
- Anterior
- Posterior
Failure of one of the lacunar cavities to merge with the others results in the development of a:
Pericardial (coelomic) cyst
Usual location of Pericardial (coelomic) cyst
Right cardiophrenic angle
Usual lining of Bronchial cyst
Pseudostratified ciliated respiratory epithelium / ciliated columnar epithelium
Congenital cysts that are usually located in the posterior mediastinum in a paravertebral location, attached to the wall of the esophagus or even embedded within the muscle layer of this organ (2)
- Gastric cyst
- Enteric cyst
Generic term that has been proposed for a congenital thymic alteration thought to be expression of a failure and/or arrest in the development of the organ
Thymic dysplasia
Main differential of thymic dysplasia that is characterized by marked lymphocytic depletion accompanied by preservation of the lobular architecture and of Hassall corpuscles
Acute Thymic Involution
Microscopic features of thymic involution in HIV infection (4):
- effacement of the corticomedullary junction
- marked lymphocytic depletion
- variable degrees of plasma cell infiltration and fibrosis
- inconspicuous Hassall corpuscles
defined as thymic enlargement beyond
the upper limits of normal for the age (as determined by weight using the Hammar table or by volumetric measurement) but accompanied by a microscopically normal gland
True thymic hyperplasia
defined as the presence of more than an occasional lymphoid follicle in the thymus independent of the size of the gland.
Thymic follicular hyperplasia
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Sharply defined, angular lobules
Thymoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Fibrous bands and capsule
Thymoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Mottling and trabeculation (caused by epithelial– lymphocyte admixture)
Thymoma
Tumors of the Anterior Mediastinum:
Nuclei - Often fine chromatin contrasting with well-defined nuclear membrane
Thymoma
Tumors of the Anterior Mediastinum:
Nuclei - Usually inconspicuous nucleoli; great variation, including spindle shape
Thymoma
Tumors of the Anterior Mediastinum:
Nuclei - Epithelial mitoses usually rare
Thymoma
Tumors of the Anterior Mediastinum:
Cytoplasm - Great variation from scant to squamoid to squamous
Thymoma
Tumors of the Anterior Mediastinum:
Cytoplasm - Intracytoplasmic cysts
emperipolesis
Thymoma
Tumors of the Anterior Mediastinum:
Cytoplasm - Glandlike spaces
Thymoma
Tumors of the Anterior Mediastinum:
Associated features - Germinal centers in surrounding thymus (in cases of myasthenia gravis)
Thymoma
Tumors of the Anterior Mediastinum:
Associated features - Incorporation of non-neoplastic thymus (13%)
Thymoma
Tumors of the Anterior Mediastinum:
Electron microscopy - Well-formed desmosomes
Thymoma
Tumors of the Anterior Mediastinum:
IHC - Keratin
Thymoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Diffuse growth
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Variable fibrosis with
occasional compartmentalizing sclerotic pattern
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Residual cystic thymus
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Nuclei - Vesicular with prominent nucleoli
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Nuclei - Marked folding of nuclei
“cloverleaf”
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Nuclei - Variable chromatin pattern
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Nuclei - Mitotic figures variable (usually readily found)
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Cytoplasm - Variable, occasionally abundant and rich in RNA (methyl green–pyronine positive)
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Associated features - Residual lymphocytes often form tight perivascular cuffs
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Associated features - Necrosis frequent
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Associated features - Markedly invasive
Large cell lymphoma
Tumors of the Anterior Mediastinum (2):
Electron microscopy - Nuclear blebs
- Large cell lymphoma
- Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum (2):
Electron microscopy - Absence of epithelial features
- Large cell lymphoma
- Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum:
IHC - B-lymphocyte markers
Large cell lymphoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Diffuse growth or pseudonodular pattern (both in lymph nodes and in thymus)
Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum:
Nuclei - Even chromatin (“dusky” at low power)
Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum:
Nuclei - Scant inconspicuous nucleoli
Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum:
Nuclei - Numerous mitotic figures
Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum:
Cytoplasm - Scant
Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum:
Associated features - Residual Hassall corpuscles
Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum:
Electron microscopy - Fine chromatin
Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum:
IHC - T-lymphocyte markers
Lymphoblastic lymphoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Extensive fibrosis with rounded lobules of tumor
Thymic Hodgkin Lymphoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Prominent cysts seen at low power
Thymic Hodgkin Lymphoma
Tumors of the Anterior Mediastinum:
Nuclei - Cytologic features— those of nodular sclerosing Hodgkin lymphoma complicated by admixture with thymic epithelium and cysts
Thymic Hodgkin Lymphoma
Tumors of the Anterior Mediastinum:
Cytoplasm - Lacunar cells often prominent
Thymic Hodgkin Lymphoma
Tumors of the Anterior Mediastinum:
Electron microscopy - Absence of epithelial
characteristics in Reed– Sternberg cells
Thymic Hodgkin Lymphoma
Tumors of the Anterior Mediastinum:
IHC - CD15, CD30
Thymic Hodgkin Lymphoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Subdivided by fine fibrous trabeculae into variable-sized compartments
Thymic Seminoma
Tumors of the Anterior Mediastinum:
Nuclei - Coarse chromatin, marked prominence of nucleoli, variable numbers of mitotic figures
Thymic Seminoma
Tumors of the Anterior Mediastinum:
Cytoplasm - Marked retraction of cytoplasm; often glycogen rich
Thymic Seminoma
Tumors of the Anterior Mediastinum:
Associated features - Germinal centers, epithelioid and giant cells
Thymic Seminoma
Tumors of the Anterior Mediastinum:
Electron microscopy - Even chromatin
Thymic Seminoma
Tumors of the Anterior Mediastinum:
Electron microscopy - Prominent nucleoli
Thymic Seminoma
Tumors of the Anterior Mediastinum:
Electron microscopy - Glycogen rich
Thymic Seminoma
Tumors of the Anterior Mediastinum:
Electron microscopy - Scant desmosomes
Thymic Seminoma
Tumors of the Anterior Mediastinum:
Electron microscopy - Only rare tonofilaments
Thymic Seminoma
Tumors of the Anterior Mediastinum:
IHC - PLAP, CD117
Thymic Seminoma
Tumors of the Anterior Mediastinum:
Patterns (LPO) - Ribbons, festoons, punctate calcified necrosis producing discrete and rounded masses of tumor
Thymic Carcinoid
Tumors of the Anterior Mediastinum:
Nuclei - Variable number of mitotic figures (note spindle cell variant)
Thymic Carcinoid
Tumors of the Anterior Mediastinum:
Nuclei - Rounded nuclei with sharp stippling chromatin
Thymic Carcinoid
Tumors of the Anterior Mediastinum:
Cytoplasm - Polyhedral cells with finely granular eosinophilic cytoplasm
Thymic Carcinoid
Tumors of the Anterior Mediastinum:
Cytoplasm - True gland formation
Thymic Carcinoid
Tumors of the Anterior Mediastinum:
Electron microscopy - Dense-core granules
Thymic Carcinoid
Tumors of the Anterior Mediastinum:
Electron microscopy - Desmosomes inconspicuous or poorly formed
Thymic Carcinoid
Tumors of the Anterior Mediastinum:
Electron microscopy - Tonofilaments only rarely prominent
Thymic Carcinoid
Tumors of the Anterior Mediastinum:
IHC - Chromogranin, Synaptophysin
Thymic Carcinoid
This IHC stain is usually restricted either to the glandlike formations of spindle thymomas or to the tumors predominantly composed of round or polygonal cells
EMA
Interdigitating cells located in the medullary portion of the more organoid thymomas
Asteroid cells
Defined as a thymic epithelial tumor exhibiting clear-cut cytologic features of malignancy
Thymic carcinoma
a receptor molecule that signals cell growth in T cells
CD5
IHC stain which is present in the majority of thymic carcinomas but absent in other types of thymoma and in carcinomas of nonthymic origin
CD5
IHC stain that is positive in 80% or more of thymic carcinomas, almost always negative in thymomas, and occasionally positive in nonthymic carcinomas
CD117 (c-kit)
a member of the tumor necrosis (TNF) family that mediates the interaction between B and T lymphocytes which is present in most thymic carcinomas but not in conventional thymomas
CD70
this form of thymic carcinoma is composed
of atypical polygonal epithelial cells arranged in characteristic epidermoid growth patterns often with associated intercellular bridges
Squamous cell carcinoma
This tumor is formed by well-defined epithelial islands with prominent
peripheral palisading, a combination of features typical of basaloid carcinomas arising in other sites including the lung.
Basaloid carcinoma
Areas of squamous and mucin-producing glandular differentiation alternate in this neoplasm
Mucoepidermoid carcinoma
large, deeply acidophilic nucleoli that are sharply outlined and perfectly round are one of the hallmarks of this neoplasm, which is also characterized by a “syncytial” appearance
Lymphoepithelioma-like carcinoma
PRESENT / ABSENT:
Keratinization in Lymphoepithelioma-like carcinoma
Absent
PRESENT / ABSENT:
Intercellular bridges in Lymphoepithelioma-like carcinoma
Absent
Positive IHCs in Lymphoepithelioma-like carcinoma (3):
- Keratins, including HMW CK such as CK5/6
- p63
- p40
This cytologically malignant tumor simulates a mesenchymal neoplasm by virtue of its diffuse pattern of growth and the prominent spindling of tumor cells
Sarcomatoid carcinoma (Carcinosarcoma)
Previous names of Metaplastic thymoma (2)
- Thymoma with pseudosarcomatous stroma
- Low-grade metaplastic thymic carcinoma
It is characterized by a biphasic epithelial and spindle cell morphology, with absence of significant atypia and low proliferation rates in both components
Metaplastic thymoma
a form of high-grade carcinoma frequently demonstrating squamous differentiation that tends to affect midline structures, most commonly the mediastinum
NUT (midline) carcinoma
This tumor shows no detectable differentiation in any specific direction
and tends to exhibit considerable pleomorphism.
Undifferentiated (Anaplastic) Carcinoma
Type A / Type B thymomas:
Thymomas in which neoplastic epithelial cells and their nuclei have a spindle/ oval shape with few, if any, non-neoplastic T cells.
Type A thymomas
Type A / Type B thymomas:
Thymomas in which neoplastic epithelial cells have a dendritic or plump (“epithelioid”) appearance and a variably conspicuous component of non-neoplastic immature T cells.
Type B thymomas
Other name of Type A thymoma (2):
- Spindle cell
- Medullary
A tumor composed of a population of neoplastic thymic epithelial cells having a spindle/oval shape, lacking nuclear atypia, and accompanied by few or no non-neoplastic lymphocytes
Type A thymoma
other name of Type AB thymoma
Mixed
A tumor in which foci having the features of type A thymoma are admixed with foci rich in lymphocytes including a significant proportion of immature T cells
Type AB thymoma
other name of Type B1 thymoma (4):
- Lymphocyte-rich
- Lymphocytic
- Predominantly Cortical
- Organoid
A tumor that resembles the normal functional thymus in that it combines large expanses having an appearance practically indistinguishable from normal thymic cortex in which cytologically bland thymic epithelial cells are evenly dispersed within a background of immature T cells and accompanied by areas resembling thymic medulla
Type B1 thymoma
other name of Type B2 thymoma
Cortical
A tumor in which the neoplastic epithelial component appears as scattered plump cell, often including small (≥3 contiguous epithelial cells) clusters, with vesicular nuclei and distinct nucleoli among a heavy population of immature T cells.
Type B2 thymoma
Type of thymoma in which perivascular spaces are common and sometimes very prominent
Type B2 thymoma
Type of thymoma in which a perivascular arrangement of tumor cells resulting in a palisading effect may be seen
Type B2 thymoma
other name of Type B3 thymoma (4):
- Epithelial
- Atypical
- Squamoid
- Well-differentiated thymic carcinoma
A type of thymoma predominantly composed of mildly atypical epithelial cells having a round or polygonal shape admixed with a minor component of immature T cells, resulting in a sheetlike growth of the neoplastic epithelial cells
Type B3 thymoma
characterized by a micronodular growth pattern in which epithelial islands are separated by lymphoid stroma that may include florid follicular hyperplasia
Micronodular thymoma
another rare subtype that is a biphasic tumor
in which solid areas of epithelial cells are variably well demarcated from cytologically bland, fibroblast-like spindle cells
Metaplastic thymoma
refers to thymomas measuring less than 0.1 cm in greatest dimension and are usually discovered as multifocal incidental findings in thymectomies from patients with myasthenia gravis
Microscopic thymoma
Other name of Microscopic thymoma
Nodular hyperplasia
A thymic tumor exhibiting clear-cut cytologic atypia and a set of cytoarchitectural features no longer specific to the thymus (as for types A, AB, and B thymomas) but rather analogous to those seen in carcinomas of other organs
Thymic carcinoma
Modified Masaoka-Koga stage:
Grossly and microscopically encapsulated tumor
Stage I
Modified Masaoka-Koga stage:
Capsular invasion
Stage II
Modified Masaoka-Koga stage:
Limited (≤3 mm) microscopic transcapsular invasion
Stage IIa
Modified Masaoka-Koga stage:
Macroscopic (microscopically confirmed) invasion into thymic or surrounding adipose tissue without pleural or pericardial involvement
Stage IIb
Modified Masaoka-Koga stage:
- Macroscopic (microscopically confirmed) invasion into neighboring organs (i.e. mediastinal pleura, pericardium, visceral pleura ± lung parenchyma, phrenic or vagus nerves, major vessels)
- adherence (i.e. fibrous attachment) to lung or other adjacent organs if (and only if) there is concomitant microscopic invasion of mediastinal pleura and/or pericardium
Stage III
Modified Masaoka-Koga stage:
Metastases
Stage IV
Modified Masaoka-Koga stage:
Pleural or pericardial metastases (i.e. nodules separate from main mass involving visceral or parietal pleura, or pericardial or epicardial surfaces)
Stage IVa
Modified Masaoka-Koga stage:
Lymphogenous (intrathoracic or extrathoracic lymph nodes) or hematogenous (pulmonary parenchymal or extrathoracic) metastases
Stage IVb
AJCC
Primary tumor (pT):
Primary tumor cannot be assessed
TX
AJCC
Primary tumor (pT):
No evidence of primary tumor
T0
AJCC
Primary tumor (pT):
-Tumor encapsulated or extending into the mediastinal fat
-may involve the mediastinal
pleura
T1
AJCC
Primary tumor (pT):
Tumor with no mediastinal pleura involvement
T1a
AJCC
Primary tumor (pT):
Tumor with direct invasion of mediastinal pleura
T1b
AJCC
Primary tumor (pT):
Tumor with direct invasion of the pericardium (either partial or full thickness)
T2
AJCC
Primary tumor (pT):
Tumor with direct invasion into any of the following:
- lung,
- brachiocephalic vein,
- superior vena cava,
- phrenic nerve,
- chest wall, or
- extrapericardial pulmonary artery or veins
T3
AJCC
Primary tumor (pT):
Tumor with invasion into any of the following:
- aorta (ascending, arch, or descending),
- arch vessels,
- intrapericardial pulmonary artery,
- myocardium,
- trachea,
- esophagus
T4
AJCC
Regional Lymph Node (N):
Regional lymph nodes cannot be assessed
NX
AJCC
Regional Lymph Node (N):
No regional lymph node metastasis
N0
AJCC
Regional Lymph Node (N):
Metastasis in anterior (perithymic) lymph nodes
N1
AJCC
Regional Lymph Node (N):
Metastasis in deep intrathoracic or cervical lymph nodes
N2
AJCC
Distant Metastasis (M):
No pleural, pericardial, or distant metastasis
M0
AJCC
Distant Metastasis (M):
Pleural, pericardial, or distant metastasis
M1
AJCC
Distant Metastasis (M):
Separate pleural or pericardial nodule(s)
M1a
AJCC
Distant Metastasis (M):
Pulmonary intraparenchymal nodule or distant organ metastasis
M1b
AJCC
T1, Level 1 structures (3):
- Thymus
- Anterior mediastinal fat
- Mediastinal pleura
AJCC
T2, level 2 structure:
-Pericardium
AJCC
T3, level 3 structures (6):
- Lung
- Brachiocephalic vein
- Superior vena cava
- Phrenic nerve
- Chest wall
- Hilar pulmonary vessels
AJCC
T4, level 4 structures (6):
- Aorta (Ascending, Arch, or Descending)
- Arch vessels
- Intrapericardial pulmonary artery
- Myocardium
- Trachea
- Esophagus
Microscopic subtype of thymoma and the likelihood of invasion:
B3>B2>B1>AB>A
Tumors in the neck:
Gender - M>F
Ectopic hamartomatous thymoma
Tumors in the neck (2):
Gender - Females more than males
- Ectopic cervical thymoma
- CASTLE
Tumors in the neck:
Gender - M=F (about the same)
SETTLE
Tumors in the neck:
Mean age - 49.9
Ectopic hamartomatous thymoma
Tumors in the neck:
Mean age - 42.7
Ectopic cervical thymoma
Tumors in the neck:
Mean age - 15
SETTLE
Tumors in the neck:
Mean age - 48.5
CASTLE
Tumors in the neck:
Anatomic location - Supraclavicular or suprasternal soft tissue
Ectopic hamartomatous thymoma
Tumors in the neck:
Major Histologic Features:
- Circumscribed
- haphazard admixture of bland-looking spindle (epithelial) cells, solid and cystic epithelial islands (commonly squamous and glandular), and mature fat cells
Ectopic hamartomatous thymoma
Tumors in the neck:
Behavior:
- Benign
- No recurrence or metastasis after excision
Ectopic hamartomatous thymoma
Tumors in the neck:
Anatomic location - Soft tissue of neck, often in a juxtathyroid location, or sometimes inside thyroid
Ectopic cervical thymoma
Tumors in the neck:
Major Histologic Features:
- Similar to mediastinal thymomas
- encapsulated or invasive
- jig-saw puzzle-like lobules
- mixture of pale epithelial cells (plump or spindled) and lymphocytes
Ectopic cervical thymoma
Tumors in the neck:
Behavior:
-Most pursue a benign course with no recurrence; exceptionally, metastasis can occur
Ectopic cervical thymoma
Tumors in the neck:
Anatomic location - Thyroid gland
SETTLE
Tumors in the neck:
Major Histologic Features:
- Encapsulated or infiltrative
- highly cellular tumor
- merging of compact or reticulated spindle (epithelial) cells with glandular elements
- mucous glands often present
- component of lymphocytes lacking
SETTLE
Tumors in the neck:
Behavior:
Protracted clinical course, with a propensity to develop delayed distant metastasis
SETTLE
Tumors in the neck:
Anatomic location - Thyroid gland (usually lower pole) and surrounding soft tissue, or soft tissues of the neck
CASTLE
Tumors in the neck:
Major Histologic Features:
- Lymphoepithelioma-like carcinoma that may show foci of squamous differentiation
- lobulation
- pushing margins
- lymphocytic infiltration often present
CASTLE
Tumors in the neck:
Behavior:
- Generally indolent tumor that can recur after long intervals
- regional lymph node metastasis occurs in about half of the cases
- occasional cases pursue a more aggressive course
CASTLE
The microscopic appearance of
this tumor is not noticeably different from that of its orthotopic mediastinal counterpart
Ectopic (cervical) thymoma
an encapsulated benign thymic lesion that can attain a huge size and can simulate radiographically cardiomegaly or pulmonary sequestration.
Thymolipoma
IHC stains helpful in distinguishing Mediastinal Seminoma (Germinoma) vs Thymic carcinoma
Postivity of Mediastinal Seminoma with:
- OCT3/4
- SALL4
defined, as in other sites, as a germ cell
tumor similar to mature teratoma but also containing immature epithelial, mesenchymal, or neural elements without a component of embryonal carcinoma
Immature teratoma
an invasive, highly necrotic neoplasm and its microscopic appearance is, by definition, poorly differentiated.
Embryonal carcinoma
IHCs for Embryonal carcinoma (6):
- Keratin
- PLAP
- OCT4
- SALL4
- CD30
- CD57 (Leu7)
IHC stains to distinguish Yolk sac tumor (endodermal sinus tumor) (2)
- OCT4-
- SALL4+
an older term used to describe mixed germ cell tumors characterized by a combination of embryonal carcinoma and teratoma (mature and/or immature), and comprises about 5% of all mediastinal germ cell tumors.
Teratocarcinoma
Subtype of Hodgkin Lymphoma nearly always present in mediastinum
Nodular sclerosis
A diffuse accumulation of mature adipose tissue that may occur in association with obesity, Cushing disease, or steroid therapy, and which can lead to a “sabre sheath” tracheal deformity radiographically
Lipomatosis
