Urothelium

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The urothelium lines the upper portion of the genitourinary tract, i.e. ureters, urinary bladder), and a bit of the lower part.

Normal urothelium

Gross

Extent of urothelium

Urethra in males
  • Pre-prostatic urethra - transitional epithelium.
  • Prostatic urethra - transitional epithelium.
  • Membranous urethra (from apex of prostate to bulb of penis (bulb of the corpus spongiosusm)) - pseudostratified columnar epithelium.
  • Spongy urethra - pseudostratified columnar epithelium (proximal) & stratified squamous (distal).

Microscopic

Features:

  • Maturation (cuboidal at base - squamoid at surface).
    • Surface cells called 'umbrella cells' (umbrella cells CK20 +ve).
  • Urothelium should be 4-5 cell layers thick.
  • +/-Prominent nucleoli.

Note:

  • Should not have a papillary architecture -- if it does it is likely cancer!
    • If it is 'papillary' -- it must have fibrovascular cores.

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URINARY BLADDER LESION, TRANSURETHRAL RESECTION:
- UROTHELIAL MUCOSA WITHIN NORMAL LIMITS.
- NEGATIVE FOR MALIGNANCY.

Micro

The sections shows urothelium with underlying tissue. The urothelium is 4-5 cells thick. Umbrella cells are present. Few mononuclear inflammatory cells are seen in the subepithelial tissue.

The urothelium has no nuclear hyperchromasia and no significant nuclear enlargement. Mitotic activity is not identified. No papillary structures are present.

Approach

Where to start

July 1st PGY-2:

  1. Urothelial carcinoma - essentially defined by increased nuclear size +/- irreg. nuclear contour.
    • Nucleoli are common in urothelium.
      • This can be confusing... prostate carcinoma has nucleoli.
    • Mitosis - these are key if the nuclear enlargement is not present.[1]
    • Cell-depleted urothelium, where the cells have shed-off--but a few remain, should raise suspicions to cancer.
      • Thickness of the urothelium, otherwise, isn't very useful for diagnosing cancer.
  2. Round structures should make you think of papillae and prompt looking for fibrovascular cores.
  3. Fibrovascular cores = papillae... may be cancer!

A checklist-like approach

  1. Papillary structure - with fibrovascular cores?
    • Nuclear pleomorphism?
      • Yes - high grade (4-5x lymphocyte) --> Dx: high grade papillary urothelial carcinoma
      • No - low grade or normal (2-3x lymphocyte) --> DDx: low grade papillary urothelial carcinoma, PUNLMP, papilloma
  2. Flat lesions?
    • Nuclear pleomorphism?
  3. Maturation to surface?
    • No --> Dx: sectioning artefact vs. flat UCC.
    • Yes --> likely benign.
  4. Normal thickness?
    • Normal is 4-5 cell layers.
  5. Nests of glandular cells
  6. Inflammation?
    • Michaelis-Gutman bodies?

Pitfalls:

  • Urothelial carcinoma of the bladder may be confused with a paraganglioma of the bladder.
    • Way to differentiate: paraganglioma = stippled chromatin, UCC = single nucleoli.

Note about terminology

  • The bladder is rather unique in that "carcinoma" is a label used for things that are non-invasive.
    • It has been suggested that many things that are called papillary urothelial carcinoma, would be better described as papillary intraurothelial neoplasia.[2]
    • If the terminology in the urinary bladder were applied to the colon, we'd call all adenomas, i.e. pre-malignant lesions, carcinomas.

Overview in tables

General categorization

Urothelial lesions can broadly be divided into:

  1. Flat lesions.
    • Lack papillae.
    • Tend to be more aggressive.
  2. Papillary lesions.
    • Must have true papillae.
    • Very common.
    • More often benign/indolent.

Flat urothelial lesions

Comparison urothelial changes - flat epithelium - benign/premalignant/cancerous:[3]

Diagnosis Nuclear enlargement
(X stromal lymphocyte)
Nucleoli size var., shape Polarity Mitoses Thickness Inflammation Other
Normal none (2x) small none, round matures to surface none/minimal 4-5 cells none -
Reactive atypia moderate, prominent (3x) prominent none, round as normal some, none atypical as normal severe, acute or chronic -
Flat urothelial hyperplasia none (2x) small none, round as normal as normal increased usu. none -
Urothelial dysplasia moderate (3x) small, some multiple mod. variation, some irregularity lost rare, none atypical as normal usu. none -
UCC in situ signif. (4-5x) +/-large marked, irregular lost common, atypical thin, thick or norm. +/- -
Invasive UCC signif. (4-5X) +/-large marked, irregular lost common, atypical thin, thick or norm. +/- stromal invasion

The bold entry is considered the key feature.

Papillary urothelial lesions

Urothelial cells in papillae - benign/premalignant/cancerous:[4][5]

Diagnosis Papillae features Papillae branching Papillae fusion Nuclear size Mitoses DDx IHC Other Key feature
Papilloma fat papillae,
thick FV core
rare none normal (2x lymphocyte) very rare basal PUNLMP, low gr. PUCC p53-, CK20+ umbrella cells cytologically normal normal cells,
fat papillae
PUNLMP slender FV core uncommon rare enlarged - uniform rare basal only papilloma, low gr. CK20+ umbrella low cellular density (@ low power) vs. low gr.[6] uniformly enlarged cell pop.,
slender papillae
Low grade PUCC slender FV core,
thick epithelium
frequent some enlarged with variation infreq., usually basal PUNLMP, high gr. -/+ p53, CK20+ umbrella +/- small nucleoli nuc. pleomorphism,
thick epithelium
High grade PUCC mixed population common common 4-5x lymphocyte,
marked pleomorphism
common, everywhere low gr., invasive UCC diffuse CK20+, p53+ in 50% nucleoli prominent marked nuclear pleomorphism

Notes:

  • FV core = fibrovascular core.
  • PUCC = papillary urothelial carcinoma.

Risk factors for urothelial carcinoma

  • Smoking.
  • Toxins.
  • Drugs, e.g. cyclophosphamide.
  • Marijuana.[7]
  • Chinese Herbs.[8]

Others:

Flat urothelial lesions

Overview

Several different benign & pre-malignant diagnoses can be made.

The World Health Organization classification is:[10]

  • Reactive urothelial atypia.
  • Flat urothelial hyperplasia.
  • Urothelial atypia of unknown significance.
  • Urothelial dysplasia (low-grade dysplasia).
  • Urothelial carcinoma in situ (high-grade dysplasia).
  • Invasive urothelial carcinoma.

Mild urothelial atypia in normal urothelium

General

Microscopic

Features:[11]

  • Umbrella cells have:
    • Mild nuclear enlargement ~3-4x lymphocyte.
    • Round/regular nuclear membranes.
    • Focally clear cytoplasm with cobwebs.
      • Clear cytoplasm with eosinophilic reticulations.
  • +/-Inflammation.
  • No mitotic activity.

DDx:

IHC

  • Ki-67 low.
  • p53 -ve.

Urothelial carcinoma in situ

  • Abbreviated CIS.

General

  • Lack papillae.

Microscopic

Features:

  • Nuclear changes key feature.
    • Enlargement of nuclei (often 4-5x the size of stromal lymphocytes) -- diagnostic.[12]
      • Normal urothelium approx. 2x the size of stromal lymphocytes.
    • Nuclear pleomorphism - marked variation in size of nuclei.
  • +/-Disordered arrangement/crowding of cells.
    • In normal urothelium the cell line-up on the basement membrane.
  • Umbrella cells often absent.
  • +/-Mitoses present.
  • +/-Enlarged nucleoli.

Note:

  • The urothelium may be "depleted", i.e. exist only of rare large cells on the basement membrane.
    • This is known as clinging urothelial carcinoma in situ.[13]

Images

www:

IHC

Features:[14]

  • p53 +ve.
  • Ki-67 high.

Benign urothelium vs. CIS:[15]

  • CK20 +ve in deep cells (23/26 cases).
    • Normal urothelium -- only the umbrella cells.
  • Ki-67 ~50% of cells - deep and superficial.
    • Normal ~10% of cells, confined to basal aspect.

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URINARY BLADDER LESION ("TUMOUR"), TRANSURETHRAL RESECTION URINARY BLADDER TUMOUR (TURBT): 
- UROTHELIAL CARCINOMA IN SITU.
- MUSCULARIS PROPRIA PRESENT.

Urothelial cell carcinoma

See urine cytology for the cytopathology.
  • Abbreviated UCC.
  • AKA urothelial carcinoma.

General

  • These lesions lack papillae and are typical flat.
  • Clinically, it may not be possible to differentiate renal pelvis urothelial carcinoma and renal cell carcinoma.

Microscopic

Features:

  • Nuclear pleomorphism - key feature.
    • Compare nuclei to one another.
  • Increased N/C ratio.
  • Lack of maturation to surface (important).
  • Cells become dyscohesive.
    • Mostly useless in my experience.

Invasion vs. in situ: Useful features - present in invasion:[16]

  • Thin-walled vessels.
  • Stromal reaction (hypercellularity).
  • Retraction artefact around the tumour cell nests.

Note:

  • The presence/absence of muscle should be commented on in biopsy specimens.
  • Adipose tissue may be seen in the lamina propria; tumour adjacent to adipose tissue on a biopsy does not imply invasion deep to the muscularis propria.[17]

DDx:

Staging

  • T1 - lamina propria.
    • Several subdivisions of T1 exist:
      • T1a - superficial or in muscularis mucosae.
      • T1b - beyond muscularis mucosae - into submucosa.
  • T2 - muscularis propria.

Subtypes of urothelial carcinoma

There are numerous subtypes:[18]

Benign patterns - mnemonic Much GIN:

  • Microcystic.
  • Small tubular/glandular.
  • Inverted.
  • Nested.
Plasmacytoid urothelial cell carcinoma

Features:

  • Abundant gray cytoplasm, eccentric nucleus.

Images:

Nested urothelial cell carcinoma
  • AKA nested variant urothelial cell carcinoma.

Features:[19]

  • High density of well-circumscribed nests.
  • Mild-to-moderate nuclear atypia.
  • +/-Foci of unequivocal conventional urothelial carcinoma.
    • Focally solid or gland fusion.
    • Moderate-to-severe nuclear atypia +/- abundant mitoses.
  • +/-Extension into the muscularis propria.

DDx:

Images

www:

IHC

Features:

  • CK7 +ve CK20 +ve.
    • CK20 may be negative in over 50% of cases with metastases.[21]

UCC vs. Prostate:

  • UCC: p63+, PSA-, PSAP-, CK7+, CK20+.
  • Prostate: p63-, PSA+, PSAP+, CK7-, CK20-.

UCC vs. RCC:

Molecular

Not used for diagnosis.

Changes:

  • 9p deletion -- site of CDKN2A[23] (AKA p16).
  • 17p deletion -- site of PT53 (AKA p53).

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High grade UCC

URINARY BLADDER LESION ("TUMOUR"), TRANSURETHRAL RESECTION URINARY BLADDER TUMOUR (TURBT): 
- INVASIVE HIGH-GRADE PAPILLARY UROTHELIAL CARCINOMA WITH SQUAMOUS DIFFERENTIATION AT LEAST INTO MUSCULARIS PROPRIA.
- LYMPHOVASCULAR INVASION PRESENT.

Nested variant

 URINARY BLADDER LESION ("TUMOUR"), TRANSURETHRAL RESECTION OF BLADDER TUMOUR (TURBT):
- INVASIVE LOW-GRADE UROTHELIAL CARCINOMA, NESTED VARIANT.
- TUMOUR PRESENT AT EDGE OF TISSUE.
- NO MUSCULARIS PROPRIA IDENTIFIED.

Papillary urothelial lesions

Papillary urothelial lesions are grouped into one of five categories (listed from good to bad prognosis):[5]

  1. Urothelial papilloma.
  2. Inverted papilloma.
  3. Papillary urothelial neoplasm of low malignant potential (PUNLMP).
    • PUNLMP is pronouced "pun-lump".
  4. Low grade papillary urothelial carcinoma.
  5. High grade papillary urothelial carcinoma.

Key characteristics:

  1. Nuclear - size/pleomorphism.
  2. Papillae branching.
  3. Papillae fusion.

Urothelial papilloma

General

  • Very rare diagnosed.
    • If the person has a history of a low grade papillary urothelial carcinoma... it is a low grade papillary urothelial carcinoma.
    • These cases are a consensus diagnosis, i.e. you show it to a colleague... if they agree you can call it.

Microscopic

Features:[5]

  • Papillary fronds.
  • Minimal branching or fusion.
  • Cytological features of normal urothelium.
    • Normal urothelium approx. 2x the size of stromal lymphocytes.[12]
  • No mitoses.
  • Thickness < 7 cells.[citation needed]

DDx:

Inverted urothelial papilloma

General

  • May be confused with papillary urothelial carcinoma with an inverted growth pattern.

Microscopic

Features:

  • Like papillomas... but grow downward.[5]
  • According to THvdK,[24] inverted papillomas never have an exophytic component; if an exophytic component is present it is urothelial carcinoma. This is disputed by one paper from Mexico that examines two cases.[25]
  • Nests have peripheral palisading of nuclei - important.

DDx:

Images

IHC

May be useful versus inverted growth pattern UCC:[26]

  • Ki-67 -ve.
  • CK20 -ve.
  • p53 -ve (rarely +ve).

Papillary urothelial neoplasm of low malignant potential

  • Abbreviated PUNLMP.
    • This is pronounced pun-lump.

General

Treatment:

Microscopic

Features:[5]

  • Rare fused papillae.
  • Infrequent mitoses.
  • Nuclei larger than papilloma - but monotonous.[31]

DDx:

Images

Low-grade papillary urothelial carcinoma

  • Abbreviated LGPUC.[32]
  • AKA low-grade papillary urothelial cell carcinoma.

High-grade papillary urothelial carcinoma

  • Abbreviated HGPUC.
  • AKA high-grade papillary urothelial cell carcinoma, abbreviated HGPUCC.

Benign urothelial lesions

The big table of cystitis:

Type Key feature DDx Reference
Florid proliferative cystitis expanded lamina propria with von Brunn's nests, cystitis cystica et glandularis von Brunn's nests, cystitis cystica et glandularis, low-grade urothelial carcinoma [33]
Polypoid cystitis wide base, height > base papillary cystitis, bullous cystitis [34]
Bullous cystitis wide base, height < base papillary cystitis, polypoid cystitis [34]
Papillary cystitis narrow base, height > base polypoid cystitis, bullous cystitis [34]
Interstitial cystitis +/-ulceration (uncommon) - requires clinical correlation urothelial CIS [35]
Follicular cystitis lymphoid follicles non-Hodgkin lymphoma [36]
Infectious cystitis dependent cause (bacterial, viral, fungal) [37]
Granulomatous cystitis granulomas tuberculosis, schistosomiasis, fungal infection, post-BCG [37]
Radiation cystitis edema, vascular congestion, +/- erosions -- acute; fibrosis in LP and detrusor -- chronic [38]

Interstitial cystitis

General

  • Chronic cystitis, culture negative.
  • Treatment difficult.[39]

Epidemiology:[40]

  • Women > men.

Symptoms:[40]

  • Urgency.
  • Frequency.
  • Pain.

Microscopic

Features:[35]

  • +/-Ulceration (uncommon).

Note:

DDx:

  • Urothelial CIS.

Follicular cystitis

Microscopic

Features:[36]

  • Lymphoid follicles in the lamina propria.

DDx:

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URINARY BLADDER, BIOPSY:
- UROTHELIAL MUCOSA WITH CHRONIC INFLAMMATION AND BENIGN LYMPHOID NODULES WITH GERMINAL CENTRE FORMATION.
- MUSCULARIS PROPRIA PRESENT.
- NEGATIVE FOR UROTHELIAL CARCINOMA IN SITU AND NEGATIVE FOR MALIGNANCY.

Polypoid cystitis

General

  • Uncommon.
  • Wide age range.
  • Benign.

Microscopic

Features:[34]

  • Polypoid urothelium-covered projections with:
    1. Broad bases.
    2. Height > base.
    3. Extensive edema.

DDx:

  • Papillary cystitis - not a broad base.
  • Bullous cystitis.

Image:

von Brunn nests

General

  • Benign.

Microscopic

Features:[41]

  • Nests of (benign) urothelium budding into the lamina propria.

Note:

  • Nests should not extend into the muscularis propria.

DDx:

IHC

Features:[42]

  • p53 -ve.
  • MIB-1 <3%.

Cystitis cystica

General

Microscopic

Features:[41]

  • Nests of urothelium within the lamina propria with cyst formation, i.e. lumens are present.

Note:

  • Nests should not extend into the muscularis propria.

DDx:

Image:

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URINARY BLADDER, BIOPSY:
- CYSTITIS CYSTICA.
- NEGATIVE FOR MALIGNANCY.

Cystitis glandularis

Cystitis cystica et glandularis
External resources
EHVSC 10173
Cystitis cystica et glandularis redirects to here.

General

  • Benign.
  • Can be thought of as cystitis cystica with mucin-secreting cells lining the cystic spaces.[43]
  • When seen in conjunction with cystitis cystica it is called cystitis cystica et glandularis.

Note:

  • There are case reports of urethritis glandularis - the same lesion in the urethra.[46][47]

Microscopic

Features:[41]

  • Nests of urothelium within the lamina propria with cyst formation, i.e. lumens are present.
  • Cyst lining cells are cuboidal and/or columnar epithelium.
    • Produce mucin.
  • +/-Goblet cells, i.e. intestinal metaplasia.[43]

Note:

  • Nests should not extend into the muscularis propria.

Image:

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URINARY BLADDER NECK, BIOPSY:
- CYSTITIS CYSTICA ET GLANDULARIS.
- NEGATIVE FOR MALIGNANCY.

Micro

The sections show urothelial mucosa with bland nests within the lamina propria with cyst formation. The stroma is edematous and has a mixed inflammatory infiltrate consisting of plasma cells, eosinophils, lymphocytes and neutrophils.

Malakoplakia

Nephrogenic adenoma

  • AKA mesonephric adenoma.
  • AKA nephrogenic metaplasia.

See also

References

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