Tadrous P.J. Diagnostic criteria handbook in histopathology: a surgical pathology vade mecum

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Respiratory and Mediastinum 89

Drugs and Toxins

Cocaine and ‘Crack Lung’

Alveolar haemorrhage, DAD, organising pneumonia

Interstitial and intra-alveolar inﬂammatory cell inﬁltration (eosinophils ++)

Bullous emphysema (fragmentat

of elastic ﬁbres) → may present with pneumothorax/mediastinum

Vascular: medial hypertrophy, 2

◦

pulm HT (± extrapulmonary eosinophilic angiitis)

Immuno: deposition of IgE in both lymphocytes and alveolar macrophages

Cannabinoids (e.g. marijuana)

Changes similar to tobacco smokers: squamous metaplasia, chronic bronchitis, RBILD, ↑ CA risk

↑ Incidence of allergic bronchopulmonary aspergillosis and other fungi (from mouldy marijuana)

± Surgical emphysema, pneumothorax and bullae (due to forced deep inhalation practices)

Narcotics (e.g. heroin)

Exacerbations of pre-existing asthma

Pulmonary oedema ± subsequent bronchiectasis

Aspiration pneumonitis risk (due to impaired consciousness during use)

Intravenous (any drug)

Emboli of foreign substances → thromboses, pulm. HT, granulomatous reactions, PMF

Talc-induced panacinar emphysema

Particles may be clear, black, basophilic (d/dg ‘bacteria’), eosinophilic, PAS +ve, carminophilic, bire-

fringent, etc. For further details on identiﬁcation, see Tomashefski and Felo, 2004

Paraquat Lung

Found in weed-killers (trademarked as Gramoxone



, Weedol



, Pathclear



, etc.)

Lowest fatal dose for adults is 17mg/kg (liver, kidney, brain and other organs are also affected)

Pneumocytes actively uptake paraquat → oxidative damage (DAD)

Early: intense vascular congestion, pulm. oedema and alveolar haemorrhage

Late (few days): hyaline membranes and intra-alveolar obliterative ﬁbrosis (elastic / Masson bodies)

Pleural Tumours

Mesothelioma

Aetiology

Asbestos, heredity, erionite, radiation, chronic inﬂam

, SV40 virus (controversial)

Subtypes

Epithelioid: tubulopapillary, solid, glandular, small cell, clear cell, deciduoid (PLAP −ve), signet ring,

lymphohistiocytic (d/dg lymphoma), pleomorphic, myxoid

Sarcomatoid: desmoplastic

, metaplastic (cartilage/bone), ﬁbrosarcoma-like, MFH-like, lymphoid-rich

General points: mitoses are scant in epithelioid; sarcomatoid may be SMA and desmin +ve; biphasic

must be differentiated from d/dg thymic carcinoma, carcinosarcoma, biphasic sarcoma and pulmonary

blastoma

Mesothelioma vs. carcinoma

+ve in meso: AB (hyaluronidase sensitive), CK5/6, calretinin (nuclear), thrombomodulin, WT1, D2-40

+ve in CA: DPAS (strong, big globule), MNF, TTF-1, pCEA, Ber-EP4, CD15, B72.3, BG8, MOC-31

AMAD-2 is +ve in most mesotheliomas but is rare in adenocarcinomas

MUC4 was expressed by 94% of lung adeno CA but not meso (i.e. 100% speciﬁc for adenoCA)

Mesothelioma may show characteristic cytogenetic changes

Ber-EP4 may be +ve in mesothelioma but never diffuse and strong (<50% of cells and usu. <25%).

It is esp. good at discriminating mesothelioma from adenocarcinoma of pulmonary origin

CK +vity in the deepest parts of the tumour is better evidence of malignant mesothelioma (cf. superﬁcial

+vity). CK5/6 is +ve in most SCC of lung, −ve in most adenocarcinomas

−ve CEA is strong evidence against adenocarcinoma

if > 50% of tumour is hypocellular

Llinares et al., 2004

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Respiratory and Mediastinum 90

Mesothelioma vs. reactive mesothelial hyperplasia

Papillary, solid and even minimally invasive forms of hyperplasia exist

Hx of prior (esp. recurrent) irritat

, effusion or disease of underlying viscus favours reactive

Radiology helps: presence of mass lesion or mesothelioma-like pattern

Necrosis in hyperplastic looking lesion = strong evidence of mesothelioma

Invasion with desmoplasia and lack of inﬂam

(sub-mesothelial cells disrupted, tumour goes into

lung etc.). True invasion is haphazard and perpendicular to the mesothelial surface (cf. parallel

entrapment)

Cytology of ﬂuid may help (see pp.359–360) as it samples the whole mesothelial surface cf. Bx

↑ Cytological atypia, mitoses and papillary arch. favour (but are not diagnostic of) mesothelioma

p53 +ve (diffuse and strong) in mesothelioma

Reaction pattern with EMA (see Figure 8.3):

Reactive Meso

EMA Staining Patterns

Mesothelioma Adenocarcinoma

FIGURE 8.3 Mesothelial immuno

Desmin +vity favours reactive mesothelial hyperplasia

over malignant mesothelioma

Desmoplastic mesothelioma vs. reactive ﬁbrous pleurisy

Generous sampling / block all tissue

Meso: invasion, collagen necrosis, atypical mitoses, organised collagen patterns (storiform, etc.)

Pleurisy: more cellular, inﬂam

, ‘maturation’ of spindle cells towards the surface, vertical capillaries

Sarcomatoid mesothelioma vs. other tumours

Diagnostic criteria for meso:

◦

chest wall/lung invasion,

◦

bland necrosis and

◦

sarcomatoid areas

Calretinin is only +ve in ≈ 50% and other mesothelial markers less so; CK and vimentin are most

reliably +ve

! But some sarcomas are CK +ve (e.g. synovial sarcoma) .

. use other markers, cytogenetics, clin./radiol.

Proliferating non-neoplastic sub-mesothelial cells (≈ ﬁbroblasts) acquire CK +vity as they migrate

towards the surface, .

. CK +ve spindle cells do not imply sarcomatoid mesothelioma. In this situation

you need:

◦

Unequivocal invasion (e.g. into lung parenchyma) and

◦

Cytological evidence of malignancy

d/dg spindle sarcomas or malignant SFT (vide infra)

d/dg: calcifying ﬁbrous pseudotumour, radiation, sarcomatoid carcinoma, melanoma, RCC

Epithelioid mesothelioma vs. papillary serous carcinoma of the peritoneum / ovary

PLAP is −ve in mesothelioma but +ve in 50% of papillary serous carcinoma

S100 is −ve in (most but not all) mesothelioma but +ve in 25% of papillary serous carcinoma

CK5/6 is −ve in peritoneal CA, +ve in 25% ovarian carcinoma and +ve in 50% of mesothelioma

Pleuropulmonary Blastoma of Infancy

Solid component: may be undiff or contain multiple sarcomas (leiomyosarcoma/RMS/chondro/

osteosarcoma)

Cystic component: lined by bland (?entrapped benign) epithelium .

. probably not truly biphasic

d/dg pulmonary blastoma: adults, biphasic (has an immature epithelial component), see p. 92

Other Tumours

Solitary ﬁbrous tumour (see SFT on p. 94 and pp. 324–325)

Multicystic mesothelial proliferation of the pleura (see peritoneal type in Chapter 11: Alimentary Tract)

Adenomatoid tumour, pseudomesotheliomatous angiosarcoma, synovial sarcoma, lymphoma,

etc.

Pulmonary Lymphoid Lesions

Reactive

LIP: mainly T-cells with aggregated B-cells (d/dg MALT which has mainly B-cells), expanding the

septa (MALToma destroys them and NSIP doesn’t expand them). Must exclude EAA. Idiopathic LIP

is very rare .

. look for a cause (HIV, CTD, etc.)

Follicular Bronchiolitis: Like LIP, this occurs in three settings: CTD, immunosuppression, idiopathic

Nodular lymphoid hyperplasia (= those few ‘pseudolymphomas’ that don’t fulﬁl the criteria for

MALToma)

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Angiocentric Lymphoid Proliferations

Grade 1: BLAG is composed of small mature lymphocytes and has the lowest Ki-67 LI of the three

Grade 2: Lymphomatoid granulomatosis (usu. an angioinvasive and angiodestructive EBV-related

T-cell-rich DLBCL +geographic necrosis ± granulomas but occ. TCL/NK tumours show this histol.)

Grade 3: Angiocentric T-cell lymphoma

MALT Lymphomas and ‘Pseudolymphoma’

Reactive MALT is induced by smoking, autoimmune disease and CFA. LIP also has ↑risk of lymphoma

Low grade (see also pp.110–112):

 clin./radiol.: age >30 years, air bronchograms

 arch: destructive masses with surrounding perilymphatic and bronchovascular bundle exten-

sion (sparing vessels), septal and subpleural inﬁltration

 ± non-necrotising transmural inﬁltrates of large vessels

 other: hyaline sclerosis, giant lamellar bodies, LEL ++ (in the lung the lymphocytes may not

look monocytoid), granulomas (not caseous), amyloid

The term pseudolymphoma was used for what we now consider to be true low grade MALToma and it

should no longer be used. (The same goes for gastric – but not cutaneous – ‘pseudolymphoma’]

High grade (= DLBCL): symptomatic, destructive growth, necrosis (see p. 113)

Other Types and d/dg of Pulmonary Lymphoma

◦

intravascular lymphoma: high grade B-cell, poor prognosis, d/dg lymphangitis carcinomatosa

◦

effusion lymphoma (PEL): a DLBCL but B markers are usu. −ve (positive for CD138, EMA, CD30,

HHV8 and clonal EBV). Assoc

with AIDS and KS

Pleural lymphoma: usu. DLBCL, assoc

with chronic inﬂammation / TB (i.e. PAL, usu. −ve for CD30,

HHV8 and EBV)

d/dg: SmCC, lymphoepithelioma-like CA, lymphohistiocytic / lymphocyte-rich mesothelioma, thy-

moma, Askin

Other Tumours

Mucinous Cystic Tumours

Benign cystadenoma: very rare, purely mucus-cell lining, no atypical features

Borderline: periph.; mucinous lining with folds, stratiﬁcat

, cytol. atypia ± microglandular solid foci

d/dg cystadenocarcinoma has obviously malignant cytology +/ frank invasion

d/dg mucinous adenocarcinoma (this is like colloid carcinoma in other organs)

d/dg bronchogenic cyst has cartilage and bronchial glands in wall

d/dg CCAM has cells other than mucinous in its lining and usu. presents in younger patients

d/dg mucus cell adenoma of bronchial glands: macro: more solid, proximal and protrudes into lumen;

micro: bland-lined mucus cysts (= dilated bronchial glands) ± papillary foci but ≈ no mitoses

Atypical Adenomatous Hyperplasia (= Bronchioalveolar Adenoma)

≤5mm diameter (if larger it is diagnosed as BAC – vide infra)

Assoc

with adenocarcinoma / SCC and metastases

Consists in Type II pneumocytes / Clara cells (but no ciliated / mucus cells)

Adenocarcinoma

WHO def

: ‘a malignant epithelial tumour with tubular, acinar, or papillary growth patterns, and/or

mucus production by the tumour cells.’

Subtypes: acinar (=mostly glandular structures ±pap / solid areas), papillary, BAC, mucinous (colloid

carcinoma) and solid (solid type must have demonstrable mucin in ‘many’ tumour cells – some deﬁne

‘many’ as ≥5 cells per hpf must stain for mucin in ≥2 hpf)

Grading: degree of solidity vs. gland formation, degree of mucin production, cytol. atypia and mitoses

Bronchioalveolar Carcinoma (BAC):

Def

: >5mm in maximum dimension, lepidic growth pattern, no well-formed glands, no invasion

Types: Mucinous (columnar, little atypia), Non-mucinous (hobnail, more atypia), mixed

Multicentric has a worse prognosis than unicentric (28% vs. 78% 5YS)

no invasion (incl. lymph / blood vascular invasion) is a 1999 WHO criterion but is controversial

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Respiratory and Mediastinum 92

Mucinous worse than non-mucinous (more likely to be multicentric)

Invasive worse than non-invasive (invasive tumours = ‘adenocarcinoma with a BAC growth pattern’)

d/dg alveolar adenoma: rare, well circ., <3cm, serum-ﬁlled cysts lined by bland ﬂat-cuboidal pneu-

mocytes ± hobnailing. ! Do not misdiagnose as d/dg lymphangioma

d/dg atypical Type II pneumocytes in ARDS / chemoRx (Type II pneumocyte hyperplasia has an

indistinct boundary, lacks tufts, has variable cytological atypia and has a background of interstitial lung

disease)

d/dg Lambertosis (local extension of bronchial ciliated cells to line alveolar septa)

Endometrioid adenocarcinoma (Pulmonary endodermal tumour resembling fetal lung,

‘Monophasic blastoma’)

Low grade endometrioid features with glycogen-rich cytoplasm; bland spindle stroma

Squamous morules showing focal NE differentiation and biotinylated nuclei

d/dg pulmonary blastoma: these are biphasic tumours of adults with complex / cribriform gland for-

mations (with elongated hyperchromatic cells as well as endometrioid clear cells ± morulae) and a

cellular mitotic mesenchymal stroma ± divergent differentiation (d/dg pleuropulmonary blastoma)

Squamous Cell Carcinoma (SCC)

Def

: a tumour with at least one of the following:

◦

Keratin production

—–

◦

Squamous pearls

◦

Intercellular bridges

Variants:  spindle cell

 lymphoepithelioma-like

 basaloid carcinoma: well-deﬁned solid islands with peripheral palisading, mitoses ++

and absence of NE features (unlike d/dg SmCC); worse prognosis cf. usual SCC

Grading ∝amount of squamous differentiation, cytological atypia, mitoses and necrosis (comedonecro-

sis is usu. seen in high grade – d/dg large cell NEC)

d/dg reactive or atypical squamous metaplasias (e.g. necrotising sialometaplasia-like lesions)

Adenosquamous Carcinoma (ASC)

Each component should comprise ≥10% of a single tumour mass (by WHO – others accept ≥5%)

Each component should fulﬁl the criteria for adenoCA or SCC; they are usually intimately admixed

d/dg MEC: ASC has well-developed adenocarcinoma (often with high grade nuclei) and SCC (±frank

keratinisation); ASC may be peripheral (as well as central) and have CIS

Mucoepidermoid Carcinoma (MEC)

Usu. a central, endobronchial and exophytic tumour (for histology, see p. 132)

Low grade MEC: many bland mucus cells (! d/dg bronchial gland adenoma doesn’t have 3 cell types)

MEC is favoured in a poorly diff tumour if there are areas of lower grade MEC differentiation

d/dg ASC: vide supra (but in some cases it may be impossible)

Undifferentiated Large Cell Carcinoma

WHO def

: ‘a malig. epithelial tumour with large nuclei, prom. nucleoli, abundant cytoplasm and usu.

well-deﬁned cell borders, without the characteristic features of SCC, SmCC or adenocarcinomas.’

Central necrosis may cause confusion with d/dg Large Cell NE Tumour (q.v.)

Variant: giant cell CA – has dyscohesive pleom. cells incl. multinucleated giant forms; poor prognosis

Carcinosarcoma / Sarcomatoid Carcinoma / Pleomorphic Carcinoma

Well-demarcated areas of spindle and epithelioid differentiation with CK +vity in both

Sarcomatoid carcinoma (= spindle cell carcinoma) has no epithelioid areas

Pleomorphic carcinoma has spindle +/ giant cells with no SCC / adenocarcinoma differentiation

Lymphangiomyomatosis (LAM, Lymphangioleiomyomatosis)

FM ± haemoptysis; complications (due to muscle constricting effects): pneumothorax, chylous

effusions; LAM is progressive unless Rx is given (e.g. progestagens) or menopause starts

Lung involvement is unusual (cf. major lymphatic ducts or deep LNs) and is a poor prognostic

Spindle cellular masses in the walls of endothelial-lined cystic spaces (lymphatic)

± Siderophages

Immuno of cellular masses: SMA +ve, HMB45 +ve (PEComa), S100 −ve

Immuno of cystic spaces lining: endothelial markers +ve

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Respiratory and Mediastinum 93

Associations: female hormones (regress post menopause), tuberose sclerosis, endocrinopathies

d/dg smooth muscle proliferations in CFA

d/dg benign metastasising leiomyoma or leiomyosarcoma (immuno for endothelial cells may help, also

non-PEComa smooth muscle tumours are usu. HMB45 −ve)

d/dg HX (immuno may help)

Pulmonary Neuroendocrine Proliferations

WHO Classiﬁcation of NE tumours

NE tumours are classiﬁed as described in the subheadings below

Any SCC or adenoCA with only focal NE differentiation = the appropriate type ‘with NE features’

unless the NE differentiation is in the form of SmCC in which case it is called ‘combined SmCC’

NE Cell Hyperplasia

‘Lentiginous’ proliferation within the airway’s BM

May be more ﬂorid with nesting but still conﬁned by the bronchial BM (else = tumourlet/carcinoid)

Tumourlets

Nodular prolif

assoc

with airways (cf. d/dg meningothelioid nodules – assoc

with septal veins)

Called ‘carcinoid’ if ≥ 5mm  (or if there is evidence of malig. behaviour e.g. LN mets)

If multiple, may be a cause of obstructive airways disease due to ﬁbrogenetic cytokines

Assoc

with bronchiectasis, carcinoid and carcinomas

Well diff NE tumours (Carcinoids)

Commoner in children and least assoc

with smoking

Typical arch: central tumours are trabecular (macro dumbbell), peripheral ones insular (may spindle)

Variants: some have an adenopapillary arch. and many others are biphasic with S100 +ve sustentacular

cells (= paraganglioid because the tumour cells are CK +ve, unlike true paragangliomas)

Other changes: oncocytic, melanin and mucin (small amounts); stromal cartilage / bone / APUDamyloid

Nuclei: ﬁnely granular ± slight clumping with small / inconspicuous nucleoli

Vessels: thin-walled and variably dilated

Paraneoplasia: carcinoid syndrome (affects left sided heart valves), Cushing’s, acromegaly, etc.

d/dg paraganglioma, adenoCA, clear cell sugar tumour, glomus tumour (esp. solid/inﬁltrating types)

d/dg SmCC (overdiagnosing SmCC is a potential pitfall in crushed bronchial biopsies)

 carcinoids may show crush artefact and dot-like CK – but not the Azzopardi phenomenon

 chromatin texture, Ki-67 LI (if <20% it is unlikely to be SmCC, if >50% it is unlikely to be

carcinoid) and stromal vessel features all help in the d/dg

 strong staining for CgA / synaptophysin, weak or −ve TTF-1 and peripheral location favour

carcinoid

Moderately diff NE tumours (Atypical carcinoids)

Clin.: lack SmCC chemosensitivty, 70% metastasise, more associated with smoking, 60% 5YS

Def

: contain mitoses (at a rate of 2–10/10 hpf) +/ necrosis

A non-WHO system requires ≥2 of: ≥5/10hpf mitoses, focal necrosis, some pleom., focal arch. loss

Nuclei: more coarsely granular / vesicular (cf. carcinoid) and has variable nucleoli

Ki-67 LI is 10–48% (i.e. intermediate between carcinoid and SmCC)

Peripheral tumours with SmCC-like cytology are likely to be atypical carcinoid (i.e. have insular /

trabecular arch.) and should be excised

d/dg SmCC: see above under carcinoid d/dg

Poorly diff NE tumours (SmCC and Large cell NE carcinoma)

Small cell carcinoma (SmCC):

 clin.: elderly, smokers, central location (rarely peripheral)

 close-packed (nuclear moulding), small to medium-sized cells in sheets, strands or single cells

 Azzopardi phenomenon (DNA encrustation of vessels) and smudging: these are not sufﬁcient

for diagnosis

 overlying epithelium may show atypical squamous metaplasia or Pagetoid inﬁltration

 nuclei: dark, ﬁne and evenly dispersed chromatin, inconspicuous/absent nucleoli, mitoses ++,

occ. giant nuclei

 vessels: some glomeruloid prloliferations / thick-walled vascular channels in cords

 ‘combined’ group have distinct SmCC and non-SmCC components (and ? worse prog.)

 immuno: CgA can be −ve (ISH is usu. +ve); +ve for CAM5.2 (paranuclear dot), CD56, NSE,

Ki-67 LI typcially >50%

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Respiratory and Mediastinum 94

 EM: NE dense core granules (50–200nm

) [squamous/mucinous features may be seen at

EM, but this does not change the diagnosis]

 d/dg lymphoma / inﬂam

/ PNET – all may show Azzopardi (do CD45, CD99)

 d/dg Merkel cell

CA: Merkel is CK20 +ve, CK7 −ve, SmCC of the lung is CK20 −ve, CK7

+ve

 d/dg non-SmCC (go by nuclear features – not cell size – see also carcinoid d/dg above)

 d/dg basaloid carcinoma (vide supra)

Large Cell NE carcinoma

 non-SmCC nuclei (i.e. peripherally clumped chromatin with prom. nucleoli), mod. cytoplasm

 arch.: well-deﬁned large groups that typically have periph. palisading and central necrosis

 atypical carcinoids with ≥11 mitoses per 10hpf (2mm

) are classiﬁed as large cell NEC.

Meningothelioid (Arachnoid) Nodules (old term = Minute Pulmonary Chemodectomas)

Interstitial nests of epithelioid cells (≈ meningiomas) assoc

with septal veins (cf. d/dg tumourlets)

Immuno: EMA and vimentin +ve (i.e. not a paraganglial phenotype)

EM: shows features of arachnoid granulations

d/dg 1

◦

meningioma is a well-deﬁned tumour usu. 3mm  ± foamy M +/ bone

d/dg glomus tumour (see Chapter 20: Skin) or paraganglioma (see Chapter 19: Endocrine)

Solitary Fibrous Tumour (Localised Fibrous Tumour / SFT)

Patternless pattern and ‘ropey’ collagen and stromal degenerations (see pp. 324–325)

Triad of positivity: CD34, Bcl-2, CD99; CK is −ve; CD34 is often −ve in high grade tumours/foci

Signs of malignancy: mitoses ≥4/10 hpf, ↑cellularity and pleom.; (p53 is usu. +ve in 1% of cells)

d/dg mesothelioma (important because Rx is different): SFT is localised, mesothelioma is diffuse; SFT

is CD34+ve, CK−ve, mesothelioma is converse: ! exceptions occur; use CPC; EM may help

d/dg: synovial sarcoma or pulmonary adenoﬁbroma (because entrapped mesothelial cells / type II

pneumocytes→ CK +ve cysts / clefts to give a biphasic or ﬁbroadenomatoid appearance in SFT)

See Chapter 21: Soft Tissues, for more d/dg and for the Calcifying Fibrous Pseudotumour variant.

Histiocytosis X (HX, Langerhans Cell Histiocytosis, Eosinophil Granuloma)

Progressive cough / dyspnoea (± pneumothorax esp. in acute / active disease); assoc

with smoking

Peribronchiolar (± perivascular) cellular masses, may be stellate, may ulcerate

Cystic spaces ± siderophages

Highly active lesion: Langerhans cells ++, ± DIP reaction

Subsiding activity: siderophages replace the Langerhans cells.

Healed lesion: stellate scar with siderophages ± eosinophils

May result in honeycomb lung

Immuno: CD1a +ve, S100 +ve (see also pp.57–58)

d/dg LAM (because they share: cellular masses, cystic spaces and siderophages)

d/dg UIP / DIP

d/dg Erdheim-Chester disease: in this the scarring follows the lymphatics, ±foamy M or Touton GC

and the M are CD68 and S100 +ve but CD1a −ve, + other anomalies in the bones, pituitary, skin,

etc.

Sclerosing Pneumocytoma (Sclerosing Haemangioma)

Asian, F>M, middle-age

Small (≈ 5cm ), well-circumscribed intraparenchymal (unrelated to bronchus)

Papillary, angiomatous and solid growth patterns

Bland round / polygonal cells without nucleoli

No mitoses or necrosis

Foamy M, ﬁbrosis, angiomatous areas

Immuno: +ve for surfactant, vimentin, EMA, ± CK, ± NE markers

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Epithelioid Haemangioendothelioma (See also Chapter 21: Soft Tissues.)

Typically multifocal/bilateral tumours with myxohyaline centres (d/dg amyloid tumour)

The periphery of the nodules are cellular and show a lobular/polypoidal intra-alveolar arch.

d/dg epithelioid mesothelioma (q.v.) – esp. if there is diffuse intrapleural growth – but this is rare

Clear Cell Tumour (Sugar Tumour)

Clear cells with inconspicuous nucleoli (no mitoses, necrosis or atypia)

Gaping vessels, little stroma

PEComa (HMB45 +ve, PAS +ve, DPAS −ve)

Intrapulmonary Thymoma

CK strong +ve (unlike d/dg most sarcomas)

No NE differentiation (unlike d/dg carcinoids)



See ‘Mediastinal Pathology’, below,

Lack atypia (unlike d/dg spindle cell carcinomas) for more on thymomas.

d/dg lymphoma: the epithelial component and phenotype of the lymphocytes in thymoma help

Other Tumours

Minor salivary gland-like tumours (see Chapter 11: Alimentary Tract)

Kaposi sarcoma: nodular or diffuse (see Chapter 21: Soft Tissues)

Squamous papilloma, Type II pneumocyte papillary adenoma (well-circ.), adenoﬁbroma, 1

◦

melanoma,

etc.

Pulmonary hyalinising granuloma: inﬂammatory pseudotumour in which hyaline collagen bundles

predominate in a trabecular pattern (see p. 310)

Frozen Section Diagnoses

d/dg adenoCA vs. carcinoid (with acini or endocrine-type atypia) and type II pneumocyte hyperplasia

d/dg SCC vs. squamous (or necrotising sialo-like) metaplasia in regenerative parenchyma

d/dg carcinoma vs. organising pneumonia (due to the ﬁbroblastic prolif

and reactive pneumocytes

mimicking desmoplasia and malignant epithelium respectively)

Necrotic lesions are usu. infective (e.g. TB, fungi, VZV), infarctive (e.g. Wegener’s) or neoplastic

Mediastinal Pathology

Sclerosing Mediastinitis (Causes)

Histoplasma, TB, autoimmune, trauma, drugs

Idiopathic (see p. 311)

d/dg sclerosing DLBCL

Thymoma

1917 Bell deﬁned thymoma as a thymic epithelial tumour that may be benign or malignant and is

typiﬁed by the presence of elements of the thymic epithelial reticulum and lymphocytes

1962 Bernatz and Lattes (B&L) classiﬁed them by the predominant cell type (spindle = good prog):

Predominantly: lymphoid / epithelial / mixed / spindle

1976 Rosai and Levine used invasiveness and ‘metastatic potential’ to classify thymomas:

Probably benign: encapsulated, non-invasive / bland spindle

Invasive  Category I: minimal invasion ± mild cytological atypia

 Category II: cytologically malignant (usu. widely invasive)

1989 M¨uller-Hermelink (M-H) used the organoid histology of the thymus and noted that aggressiveness

∝ cortical differentiation:

Medullary = WHO Type A

Composite = WHO Type AB

Predominantly cortical (organoid) = WHO Type B1

Cortical = WHO Type B2

Well-diff Thymic Carcinoma = WHO Type B3

1999 WHO essentially follows M-H but does away with the names (because it is uncertain whether

thymoma differentiationtruly resembles normal thymichistologyand because the term ‘well-diffthymic

carcinoma’ (WDTC) is inappropriate for a thymoma because usual-type thymic carcinomas are very

aggressive and some series have lumped WDTC with other thymic carcinomas thereby muddying the

results)

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Respiratory and Mediastinum 96

Common features for thymomas:

 organoid growth pattern (even invasive foci are organoid)

 ﬁbrous septa

 EMA +ve microcysts

 CD20 +ve epithelial cells (CD20 may be −ve in type A/B), also +ve for CK (e.g. MNF116)

 scattered CD20 +ve B-cells

 perivascular serum lakes (increase in prominence from medullary to cortical differentiation)

 follicular hyperplasia and MG are assoc

with cortical differentiation

 red cell aplasia and hypogammaglobulinaemia are assoc

with medullary differentiation

Medullary thymoma (Type A)

 non-invasive

 pericellular reticulin is present (cf. type B3)

 few lymphocytes (these are of mature phenotype: −ve for Tdt, CD99 and CD1a)

 no Hassall’s corpuscles (HC) and no foci of epidermoid differentiation.

 differs from B&L ‘predom. spindle’ in that the latter also includes spindle cell WDTC

Composite (Type A/B)

 two distinct components:

1. medullary (may form cellular ‘septa’ dividing up the cortical areas)

2. lymphocyte rich areas with ‘starry sky’ and stellate epithelial cells with open nuclei

 the cortical component has immature T-cells (+ve for CD2, CD3, Tdt, CD99 and CD1a)

 no HC and no foci of epidermoid differentiation.

Predominantly Cortical – Organoid Thymoma (Type B1)

 large tumours which typically show local invasion

 full range of differentiation of normal thymus incl. medullary islands containing HC

 well-formed lobules, thin septa, lymphocyte rich (immature T-cells)

 epithelial cells (and nucleoli) are smaller than in cortical thymoma

Cortical (Type B2)

 invasion is the rule

 lobular architecture, medullary differentiation much less obvious

 large epithelial cells with prominent eosinophilic nucleoli

 epidermoid differentiation at periphery of lobules

 immature lymphocytes (fewer than B1) and lymphoid follicles (esp. with MG)

WDTC (Type B3)

 sheets of large epithelial cells with a squamous quality (±keratin) and mitoses and mild atypia

 sclerosis is prominent

 palisading along septa and around perivascular serum lakes

 small numbers of immature T-cells

 spindle cell variants can mimic medullary but cells are large with mild cytological atypia

 lack pericellular reticulin (cf. type A)

Invasive thymoma

Lobular organoid inﬁltration into fat / surrounding tissue

‘Naked’ lobules (lack a surrounding ﬁbrous mantle)

Thymic Carcinoma

Cytological atypia

CD5 +ve epithelial cells occur in 60–80% of cases

C-kit +ve epithelial cells (membranous) in 86% (−ve in d/dg thymoma)

Usual type is SCC:  lacks immature thymic lymphocytes

 has prominent intercellular bridges

 shows a desmoplastic response when invading

 has an inﬁltrative (cf. pushing) invasive margin

 tumour cell islands separated by ﬁbrous septa (i.e. some organoid features)

d/dg WDTC – see points above

d/dg 2

◦

SCC: has more tendency to necrosis, less organoid, CD5 −ve, clinical Hx

d/dg borderline thymic epithelial tumour (atypical thymoma) – features in between thymic carcinoma

and thymoma (rare)

Other types include: lymphoepithelioma-like, sarcomatoid / carcinosarcoma, basaloid, clear cell, mu-

coepidermoid, etc.

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Respiratory and Mediastinum 97

Other Mediastinal / Thymic Mass Lesions

Lymphomas: Hodgkin’s (esp. NSHL), T-ALL, DLBCL (sclerosing)

Castleman’s disease

Carcinoid (often atypical ± Cushing’s syndrome)

Germ cell tumours (teratoma, seminoma, YST)

Thymolipoma

Thymic hyperplasia

Cysts, incl. congenital ± PEH (! d/dg thymoma/carcinoma/carcinoid arising in the wall)

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