Mediastinal Abnormalities

Question 1

Thymoma

Answer 1

Pathology:

• Most common primary anterior mediatinal malignancty
• Macro:
  
  • Necrosis/hemorrhage/cystic change (30-40%)
  • Encapsulated thymoma: mass surrounded by fibrous capsule
  • Invasive thymoma: tumour extension through capsule and into mediastinal fat and surrounding organs/pleura
• Micro:
  
  • WHO histological classification based on epithelial cell morphology, cellular atypia and proportion of epithelia cells to lymphocytes
  • Type A: round/epithelioid tumours
  • Type B: oval/spindle tumour cells
• Paraneoplastic syndrome:
  
  • Myasthenia gravis (30-50%) - 15% of MG have thymoma
  • Hypogammaglobulinemia (10%)
  • pure red cell aplasia

Epi:

• Older population: 50-70
• M=F
• Rare <1% adults malignancies

Clinical:

• Incidental
• Compression/invasion of adjacent structures: esophagus, air way, SVC, phrenic nerve
• Prognosis relatively good (dependent on staging)

CECT:

• Prevascular mediastinal soft tissue mass: abuts superior pericardium/great vessels
• Homogenous or heterogenous enhancment/attenuation: necrosis/hemorrhagic/cystic changes
• +/- calcifications: curvilinear/course/punctate
• Evidence of invasion: vascular, pleural, pericardial, pulmonary
• No associated lymphadenopathy or pleural effusion

MRI:

• T1: low to intermediate signal
• No signal drop out on oppose phased imaging –> suggests hyperplasia
• T2FS: differentiates from adj fat

DDx:

• Thymic carcinoma
• Thymic carcinoid
• Lymphoma
• Malignant germ cell tumour
• Thymic hyperplasia
• Thyroid malignancy/ectopia

Question 2

TERATOMA

Answer 2

Pathology:

• Eitiology:
  
  • postulated: rests of primitive germ cells left in mediastinu mdruing migration of yolk sac endoderm to urogenital ridge
• Primary germ cell neoplasm containing tissues derived from 2+ germinal layers
  
  • Ectoderm: hair, skin, teeth
  • Mesoderm: cartilage, bone, muscle
  • Endoderm: Bronchial/gI epithelium, mucous glands, pancreatic tissue
• Gross:
  
  • Macroscopic cysts/hemorrhage/necrosis
  • Lipid rich sebaceous material
  • Soft tissue components: hair, bone, teeth
• Associations: Klinefelter syndrome (Rare)
• Pathologic classification:
  
  • Mature Teratoma: 70% of mediastinal germ cell tumours, well-differentiated tissues
  • Immature teratoma: contains anaplastic immature elements (most commonly neuroectoderm)
  • Teratoma with malignant component
  • Teratoma with malignant mesenchymal coponent
  • Malignant immature teratoma

Epi:

• Children/young adults
• M=F

CT:

• Well-defined, unilateral prevascular mass
• Smooth/lobular borders
• Uni or multilocular
• Heterogenous attenuation:
  
  • Fluid-cyst (90%)
  • Fat attenuation cyst (75%) - fat-fluid level is diagnostic (10%)
  • Calcification (50%): teeth/bone is relatively rare
  • Soft tissue component including sepations/wall enhancment
• Malignant component:
  
  • lymphadenopathy
  • dominant solid component
  • Poorly defined
  • local invasion

MRI: helpful to charaacterise fat lesions

Top DDX:

• Thymic lesions: neoplasm, cyst
• Mediastinal lymphangioma
• Other germ-cell tumours
• Lipoma
• mets

Question 3

Seminoma

Answer 3

Pathology :

• Postulated eitiology: failure of migration of primodrial cell along urogential ridge vs reverse migration of mature testicular germ cells
• Gross:
  
  • large, unencapsulateed and well-circumscribed mass.
  • RARE: cystic, hemorrhagic or necrotic chnge
• Micro: Uniform round/polyhedral cells

Epi: 90% men aged 20-40

Clinical:

• Majority metastatic at diagnosis
• 90% 5 year survival in absecen of extrapulmonary mets
• Rx: chemoradiotherapy

Imaging:

• Large, lobular and mildly enhancing anterior mediastinal mass
• RARE: cysts, calclications, necrosis, hemorrhage
• Aassociated local mass effect
• Mediastinal lymphadenopathy
• MRI ; homogenous, T2 hypointense, Contrast enhancing septa

DDx:

• Thymoma
• Lymphoma
• Teratoma
• Thyroid

Question 4

Non-seminomatous Malignant Germ Cell Neoplasm

Answer 4

Pathology:

• Mutliple types: Primary mediastinal yolk sac tumor, choriocarcinoma, embryonal carcinoma, mixed type gem cell neoplasm
• Unknown eitiology
• Associations:
  
  • Elevated BhCG, AFP
  • Klinefelter syndromechronous testicular GCN
  • Hematological disorders
  • Meta
• Macro: big, necrotic, locally invasive
• Micro: dependent on type

Epi: Age 20-40, Males, less c ommon than teratoma/seminoma

Clinical:

• MEtastatic at diagnosis
• Rx: chemotherapy + surgical resection
• 45% 5 year progression free survival

Imaging:

• Heterogenous, large anterior mediastinal mass
• Nodular peripheral enhancment
• Central low attenuation: hemorrhage/necrosis
• Locally invasive
• Lymphadenopathy
• Pleural/pericardial effusion
• Pulmonary mets

Question 5

Neurogenic tumours (thorax)

Answer 5

• Nerve sheath tumours:
  
  • Schwannoma (most common)
  • Malignant nerve sheath neoplasm)
• Sympathetic ganglion neoplasm
• Paraganglioma
• Neurofibroma

Schwanoma:

CT:

• Spherical/elongated paravertebral mass + widening of neural foramen
• Dumb-bell morphology with exteension into spinal canal
• Low attenuation: Lipidic or cystic degenration
• Variable enhancment

MRI:

• T1: variable, isointense to spinal cord
• T2: intermediate to high SI
• Fascicular sign: multiple hypointense small ring-like structure
• Look for intraspinal/extra dural/cord involvement

Difficult to differentiate from neurofibroma

Question 6

Extramedullary Hematopoesis

Answer 6

Pathology:

• Eitiology: unknown
• Association:
  
  • Common: myelofibrosis, B-thalassemia, hereditary spherocytosis, congentila hemolytic anaemia, sickle cell anaemia
  • Less common: lymphoma, leukaemia, Gaucher disease, pagets disease, rickets, hyperPTH, pernicious anemia

Epi:

• 30-60
• Ethnicity: thalassemia (mediterranean), sickle-cell disease (african american)
• Prior splenectomy

Imaging:

• Location: typically costovertebral junctions/ paravertebral, inferior to 6th rib
• Well-marginated soft tissue masses
• Rib expansion
• Fatty degeneration - ‘burned out’ lesions
• Variable enhancement
• Pulmonary invovlement rare.
• MRI:
  
  • Fat replacement: T1/T2 high SI
  • Iron deposition: T1/T2 low SI
  • Assess intraspinal extension

Question 7

Neurofibromatosis 1

Answer 7

Pathology:

• Multisystem neurocutaneous disorder and the most common phakomatosis
• Genetics;
  
  • ​Gene locus on chromosome 17q11.2
  • Produces Neurofibromin –> acts as a tumor suppressor of RAS/MAPK pathway
  • Inactivation of this gene (50% spontaneous mutation): increases predisposition to tumor development.
  • Autosominal dominant
• Predominantly harmatomatous disroder that invovles ecto and mesoderms. 3 types of neurofibromas:
  
  • Localised neurofibroma (cutaneous): dermis/subcutis
  • Diffuse neurofibroma (subcutaneous): subcutis
  • Plexiform neurofibroma: pathognomonic if present
• ​Micro:
  
  • Diffuse Fusiform enlargment of nerves
  • Neuronal axons surrounded and displaced by disorganised schwann cells + matrix (differentiation of plexiform neurofibromas from neurofibromas)
  • MPNST: marbleized pattern, cells may be spindle-shaped/rounded/fusiform
• Associations:
  
  • Learning disabilties (50%)
  • Renal artery stenosis (1%)

Epid: earlier age of onset than NF2, 97% meet criteria by 8 years

Diagnosis requires 2/7:

• >6 Cafe au lait macules
• 2+ neurofibroma or 1 plexiform neurofibroma
• Axillary/inguinal freckling
• Optic glioma
• 2+ Lisch nodules (harmatomas of iris)
• Distintive osseous lesions: spnehoid wing dysplasia, cortical thinning of long bones +/- psuedoarthrosis
• 1st degree relative with NF1

Neoplasms:

• Malignant peripheral nerve sheath turmour (MPNST): 10% life time risk –> leading caues of death
• Phaeochromocytoma
• Wilms Tumor
• Rhabdomyosarcoma
• Renal AML
• Glioma:
  
  • JPA
  • Optic nerve glioma
  • Diffuse brain stem glioma
  • spinal astrocytoma and spinal pilocytic astrocytoma
• Carcinoid
• Leiomyoma
• Leiomyosarocma
• Ganglioma
• Leukaemia

Imaging:

• Breast: Neurofibromatosis
• Skin: cutaneous/subcutaneous neurofibormas
• Skeletal:
  
  • Scoliosis
  • Posteiror vertebral scalloping
  • Hypoplastic posterior elements
  • Enlarged neural foramina
  • Ribbon rib deformity, rib notching, dysplasia
  • Tibial pseudoarthrosis
  • Bony dysplasia: typically tibia
  • Severe bowing of gracile bones
  • Multiple non-ossifying fibromas
• CNS:
  
  • Focal areas of signal intensity (FASI): areas of high T2/FLAIR in deep white matter, basal ganglia, CC.
  • Optic Nerve Glioma
  • Sphenoid wing dysplasia
  • Lambdoid suture defects
  • Dural calcificaitons at vertex
  • Moyo-moya phenomenon (rare)
  • Buphthalmos
  • Dural ectasia
• Thoracic:
  
  • Mediastinal mass:
    
    • Neurofibroma: paravetebral masses extending into spinal canal, dumbell-shaped, widening of neural foramina +/- calcification
    • Lateral thoracic meningocoele
    • Extra-adrenal phaeochromocytoma
  • Lung parenchymal disease (20%)
    
    • Bilateral fibosis +/- honey combing (lower zone)
    • Bullae formation (upper zone)
    • Apical neurofibromas
    • Lung nodules: consider metastatic MPNST
• Vascular:
  
  • Aneurysms/AVM
  • Renal artery stenosis
  • Coarctation

MRI NEUROFIBROMA:

• T1: variable SI
• T2: target sign (central low and peripheral high SI)
• T1 + Gd: homogenous enhancment

Question 8

LYMPHOMA LYMPH NODE GROUPS (Lugano Classification)

Answer 8

• Waldeyer Ring: tonsils, base of tongue, nasopharynx
• Ipsilateral cervical, supraclavicular, occipital, preauricular LN
• Ipsilaeral Infraclavicular
• Axillary and pectoral
• Mediastinal
• Hilar
• Para-aortic
• Mesenteric
• Spleen
• Iliac
• Inguinal and femoral
• Popliteal
• Epitrochlear
• Epitrohcelar + brachial

Question 9

Lymphoma

Answer 9

Hodgkins:

• Bimodal distribution: 15-33 and >55
• Micro: Reed-sternberg cells
• Asociation with EBV infection
• Subtypes:
  
  • Classical: nodular sclerosing >> mixed cellularity > lymphocyte-rich > lymphocyte depleted
  • Non-classical: nodular lymphocyte predominant

Non-Hodgkins: linked to altered immunity, environmental exposure, older population

• Diffuse Large B-Cell Lymphoma (30%)
• Follicular lymphoma (20%)
• Peripheral T-cell lymphoma (<15%)
• Mantle cell lymphoma
• Anaplastic large cell NHL
• Burkitt lymphoma (highly aggressive)
• SLL

Question 10

Mediastinal Fibrosis

Answer 10

Pathology:

• Eitiology:
  
  • Histoplasma Capsulatum infection
  • Other fungal infections
  • Uncommon causes:
    
    • rheumatic fever
    • Behcet Disease
    • Radiation therapy
    • Trauma
    • Hodgkin lymphoma
    • Drug reaction
• Associations: other fibroinflammatory disorders
  
  • Retroperitoneal Fibrosis
  • Sclerosing Cholangitis
  • Riedell Thyroiditis
  • Orbital pseudotumor
• Micro:
  
  • infiltration + obliteration of adipose tissue by fibrous tissue + mononuclear cell infiltrate
  • Stage 1: edematous fibromyxoid tissue
  • Stage 2: mediastinal structures infiltrated and surrounded by eosinophilic hyaline material
  • Stage 3: Dense paucicellular collagen

CECT:

• Infitrated mediastinal soft tissue: surrounds/invades mediastinal structures and obliterates mediastinal fat planes
• 2 patterns:
  
  • Focal (82%): soft tissue mass, usually calcified, variable enhancment
  • Diffuse (18%): diffusing infiltrating soft tissue mass, uncommon calcification
• Mass effect:
  
  • SVCO + collateralisation
  • Tracheobronchial tree narrowing
  • Pulmonary vessels –> infarction
  • Esophageal (esophagram)

DDx:

• Lymphoma
• Mediastinal carcinomas
• Elastofibroma and fibromatosis

Question 11

Pericardial Cyst

Answer 11

Pathology:

• Eitiology:
  
  • Benign congenital mediastinal cyst
  • Anomolous outpouching of parietal pericardium
  • Occurs 4th week of gestation
• Gross: connected to pericardium, commiunication is rarely visible
• Micro: fibrous tissue lined by mesothelium, differentiation from forefut duplication cyst by based on componsition of cyst wall.

Imaging: exclude cystic neoplasm with enhancing nodules

• CT:
  
  • Location: abuts pericardium, cardiophrenic angle
  • Smoothly marginated
  • Imperceptible wall
  • Homogenmous water attenutation +/- septations
  • NO mural nodules
  • No internal enhancement
  • No calcifications
  • No lymphadenopathy
• MRI:
  
  • T1: homogenous low to intermediate SI
  • T2: homogenous, high SI +/- septations of low SI
  • T1 + Gd: no internal enhancment

DDx:

• Mediastinal fat pad
• Morgagni Hernia
• Foregut duplication cyst
• Thymic cyst
• Hydatidosis

Question 12

Thymic Cyst

Answer 12

Pathology:

• Congenital: thymopharyngeal duct embryonic remnants
• Acquired:
  
  • Inflammatory/degenerative change
  • Neoplastic
• Macro:
  
  • Congenital: unilocular cyst, thin wall, clear fluid content
  • Acquired: multilocular, thick fibrous wall, internal septal, turbid/gelatinous fluid
• Micro: variable lining epithelium, thymic tissue in wall

Imaging:

• CT:
  
  • Well-defined, ovoid/spherical mediastinal mass (typically anterior)
  • Thin or imperceptible wall
  • Homogenous water attenutation (high attenutation from hemorrhage/infection)
  • +/- septations (uni vs multilocular cyst)
  • Non-enhancement
• MRI
  
  • T1: homogenous low SI, high SI with hemorrhage/infection
  • T2: homogenous high SI, low SI wall/septa

DDx:

• Cystic anterior mediastinal mass: thymoma, teratoma, lymphoma
• Lymphangioma
• Pericardial cyst
• Aneurysm
• Forefut duplication cyst

Question 13

Achalasia

Answer 13

Pathology:

• Unknown eitiology: myenteric plexus neuropathy with incomplete relaxation of lower esophageal sphincter
• Esophageal motility disorder and dilatation
• Micro: reduced ganglion cells in myenteric esophageal plexus
• Pseudoachalasia: involvement of GEJ by other abnormaltities

Epi: younger patients, M=F

Clinical:

• Dysphagia, halitosis, Recurrent aspiration
• Rx: muscle relaxant, pneumatic dilatation, Myotomy

Imaging:

• Esophagram:
  
  • Markedly dialted esophagus
  • Absent primary peristalsis
  • Bird-beak deformity of distal esophagus
• CT:
  
  • Esophageal dilatation with air-fluid level
  • Normal wall thickeness
  • Abrupt smooth narrowing of distal esophagus
  • Complications:
    
    • Malignancy (SCC)
    • Aspiration pneumonia
    • Iatrogenic perforation

Question 14

Mediastinal Lipomatosis

Answer 14

Pathology:

• Eitiology:
  
  • Obesity
  • Cushings syndrome
• Diffuse fatty infiltration without surrounding capsule
• Mature adipocytes and cellular hyperplasia

Imaging:

• Homogenous fat attenuation
• No compression or invasion of adjacent structures
• MRI: High T1/T2 SI, signal drop out with fat suppression

DDx:

• Fat containg mediastinal mass (Mature teratoma, liposarcoma, thymolipoma, lipoblastoma, hibernoma)
• Mediastinal lymphadenopathy
• Mediastinitis