Penile Pathology

Inflammatory and Infectious Mechanisms

• Balanoposthitis results from breakdown of normal epithelial barriers and disruption of commensal flora homeostasis, with candidal overgrowth promoted by phimosis-induced warm, moist microenvironment and impaired local immunity; histologically characterized by acute neutrophilic infiltration with candidal pseudohyphae in the stratum corneum
• Peyronie disease involves aberrant wound healing with excessive fibrosis in the tunica albuginea; proposed mechanisms include penile trauma (often subclinical), recruitment of fibroblasts and myofibroblasts via TGF-β signaling, abnormal collagen cross-linking (elevated lysyl oxidase activity), and defective fibrinolysis; results in hyalinized collagen deposition with relative sparing of elastic fibers leading to mechanical penile curvature and functional impotence
• Erectile dysfunction (ED) pathophysiology varies by etiology: vasculogenic ED involves endothelial dysfunction with reduced nitric oxide (NO) bioavailability and impaired smooth muscle relaxation; neurogenic ED reflects disrupted autonomic signaling; cavernosal fibrosis results in decreased compliance and venous leak

Neoplastic Mechanisms

• Squamous cell carcinoma (SCC) development involves multi-step carcinogenesis: HPV-16/18 infection in basaloid/warty subtypes induces viral oncoproteins (E6/E7) that inactivate p53 and Rb; differentiated SCC typically arises from chronic irritation (phimosis, balanitis xerotica obliterans) with p53 mutations and oxidative stress; field effect ensures high recurrence risk
• Penile intraepithelial neoplasia (PeIN) represents clonal proliferation of atypical keratinocytes confined to epithelium, classified as differentiated (associated with chronic inflammation/lichen sclerosus) or undifferentiated (HPV-associated) based on morphology and molecular signature; progression risk to invasive SCC approximately 5-10% in differentiated type, higher in basaloid/warty variants
• Melanoma demonstrates increased mitotic rate, cytologic atypia, and irregular nesting; tends toward aggressive biological behavior with early lymphatic invasion due to rich penile lymphatic plexus

Developmental Pathophysiology

• Hypospadias/epispadias result from incomplete fusion of urethral folds (hypospadias) or dorsal induction defects (epispadias) during weeks 8-14 of embryogenesis; molecular mechanisms involve disrupted sonic hedgehog (SHH) signaling, androgen receptor dysfunction, and abnormal fibroblast growth factor (FGF) signaling
• Phimosis involves circumferential fibrosis of the prepuce; primary phimosis reflects normal developmental adhesions resolving by age 3-5 in most children; secondary phimosis results from chronic inflammation (balanitis, lichen sclerosus) inducing collagen deposition and scar contracture

Infectious Causes

• HPV infection (HPV-16, -18, -31, -33): major cofactor in basaloid and warty SCC, associated with VIN; causal role established through integration of viral genome into chromosomal DNA with disruption of tumor suppressors
• HSV-1/HSV-2: causes herpetic balanitis with vesicular lesions; risk factors include unprotected sexual contact and immunosuppression
• Treponema pallidum: primary chancre presents as solitary, indurated ulcer with "rolled borders"; secondary syphilis may involve penile lesions
• Haemophilus ducreyi: haemophilus ducreyi causes chancroid with multiple tender ulcers; endemic in developing nations
• Candida albicans: opportunistic pathogen in uncircumcised males, diabetics, and immunocompromised patients

Inflammatory/Dermatologic Causes

• Lichen sclerosus (balanitis xerotica obliterans, BXO): chronic scleroinflammatory condition with increased risk of SCC (1-5% malignant transformation); histology shows vacuolar degeneration of basal keratinocytes, homogenized dermal collagen (hyalinized zone), and T-lymphocytic infiltrate
• Lichen planus: mucocutaneous manifestation; erosive variant carries malignant potential
• Fixed drug eruption: self-limited reaction to medications
• Psoriasis: chronic inflammatory condition; may manifest as erosive or exudative penile lesions
• Contact dermatitis/irritant dermatitis: common from contraceptive preparations, latex, topical medications

Vascular/Functional Causes

• Peyronie disease risk factors: penile trauma (reported in 10-25% of cases, may be iatrogenic from injections), smoking, diabetes mellitus, hyperlipidemia, PDE-5 inhibitor use (controversial), genetic predisposition (Dupuytren contracture association), and elevated TGF-β signaling
• Erectile dysfunction: multifactorial etiology including vasculogenic disease (atherosclerosis, endothelial dysfunction), neurogenic causes (diabetes neuropathy, spinal cord injury), cavernosal fibrosis, and psychogenic factors
• Priapism: prolonged pathological erection; ischemic (low-flow) priapism results from impaired cavernosal veno-occlusive mechanism or arteriovenous malformation; associated with sickle cell disease, malignancy, or idiopathic causes

Neoplastic Risk Factors

• HPV seropositivity: present in 70-90% of basaloid and warty SCC; only 5-15% of differentiated SCC
• Phimosis: mechanical risk factor for SCC (odds ratio 10-40x), particularly in underdeveloped countries with poor hygiene; proposed mechanisms include chronic irritation, chronic inflammation, and impaired surveillance
• Balanitis/balanoposthitis: chronic recurrent infection increases malignant transformation risk
• Lichen sclerosus/BXO: predisposes to differentiated SCC through chronic inflammatory fibrosis
• Smoking: synergistic carcinogenic effect with HPV
• Age: peak incidence SCC 40-70 years
• Geographic variation: higher incidence in Central/South America, Africa, and Asia; lower incidence in circumcised populations

Congenital Causes

• Undescended testis or cryptorchidism: increases penile malignancy risk; may present with concurrent penile abnormalities
• Exstrophy-epispadias complex: high risk of adenocarcinoma and SCC in bladder/penile remnants
• Congenital penile curvature: distinguishable from Peyronie disease by congenital onset, absence of palpable plaque, and lack of progression

Infectious Presentations

• Herpetic balanitis: grouped vesicles with erythematous base progressing to painful erosions; accompanied by dysuria, systemic symptoms (fever, lymphadenopathy); may recur with prodromal paresthesias; Tzanck smear shows multinucleated giant cells (not specific); viral culture or PCR confirms diagnosis
• Candidal balanoposthitis: erythema with satellite pustules and white exudate (pseudomembrane); pruritus and dysuria; typically in uncircumcised males with poor hygiene or diabetes; potassium hydroxide (KOH) preparation demonstrates budding yeast and pseudohyphae
• Syphilis—primary chancre: solitary, indurated, painless ulcer with "rolled" hyperkeratotic borders and beefy-red granulation tissue base; clean appearance without purulent drainage; accompanied by regional lymphadenopathy (rubbery, non-suppurative); darkfield microscopy demonstrates motile spirochetes; serologies positive after 4-6 weeks (RPR/VDRL followed by confirmatory FTA-ABS or TP-PA)
• Chancroid (Haemophilus ducreyi): multiple painful, purulent ulcers with ragged borders; suppurative inguinal lymphadenopathy ("buboes"); gram-stain shows gram-negative coccobacilli in "railroad tracks" pattern; culture requires selective media (chocolate agar with antibiotics)

Inflammatory/Dermatologic Presentations

• Lichen sclerosus (BXO): progressive whitish, atrophic patches with characteristic "cigarette paper" surface; symptoms range from asymptomatic to painful erosions; dyspareunia in partners; may progress to urethral stricture or meatal stenosis; histology pathognomonic with sclerotic, hyalinized dermal zone, vacuolar degeneration of basal layer, and dense lymphocytic infiltrate in superficial dermis
• Peyronie disease: palpable, indurated fibrotic plaque (typically on dorsal surface) that may be tender in acute phase; associated penile curvature, shortening, or erectile dysfunction; psychosexual morbidity including depression and anxiety; acute phase (months 0-6) may show inflammation; chronic phase (>6 months) demonstrates fibrosis without inflammation; imaging (ultrasound, MRI) reveals plaque location and severity
• Lichen planus: violaceous papules with reticular surface ("Wickham striae"); erosive variant particularly symptomatic; histology shows band-like lymphocytic infiltrate (lichenoid pattern) with colloid bodies (Civatte bodies) at dermoepidermal junction and basal cell apoptosis

Neoplastic Presentations

• Penile SCC: presents as ulcerative, nodular, or fungating lesion typically on glans or prepuce; may have intervening phimosis; differential diagnosis includes benign penile lesions (warts, condylomata), which distinguishes by invasive histology; early lesions may be small and easily missed; symptoms include pain, bleeding, purulent drainage, or urinary obstruction; regional lymphadenopathy present in 25-30% at diagnosis but does not imply metastasis (reactive hyperplasia); distant metastases (lungs, liver, bone) occur late
• Basaloid variant: small blue cells in nests; HPV-associated; more aggressive
• Warty variant: prominent keratinization with fibrovascular cores; HPV-associated; favorable prognosis
• Differentiated (keratinizing) variant: well-differentiated squamous epithelium with prominent keratinization; associated with lichen sclerosus; less HPV association; intermediate prognosis
• Sarcomatoid variant: spindle cell morphology; poorest prognosis
• Penile intraepithelial neoplasia (PeIN/VIN): asymptomatic or mildly symptomatic reddish, velvety patches or plaques; may progress to invasive SCC; histologically shows full-thickness atypia of epithelium with hyperkeratosis, parakeratosis, and loss of maturation
• Melanoma: irregular, pigmented lesion with features of ABCDE criteria; often diagnosed at advanced stage; worse prognosis than cutaneous melanoma elsewhere due to rich lymphatic drainage
• Basal cell carcinoma: uncommon; typically nodular with central ulceration ("rodent ulcer"); slower growth than SCC

Vascular/Functional Presentations

• Priapism: persistent, painful erection unrelated to sexual stimulation; ischemic (low-flow) priapism: dark, deoxygenated corpora cavernosa with severe pain; requires emergency intervention to prevent fibrosis and permanent ED; non-ischemic (high-flow) priapism: maintained penile rigidity from arterial-cavernous fistula; painless or mildly painful; less urgent but may self-resolve
• Erectile dysfunction: inability to achieve or maintain erection sufficient for intercourse; vasculogenic ED correlates with endothelial dysfunction, reduced NO bioavailability, increased phosphodiesterase activity, and smooth muscle apoptosis; neurogenic ED involves autonomic dysfunction; cavernosal fibrosis results in decreased compliance; nocturnal penile tumescence (NPT) testing may help distinguish psychogenic from organic ED

Congenital Presentations

• Hypospadias: urethral meatus on ventral surface of penis (glandular, penile shaft, or penoscrotal); may present with altered urinary stream, difficulty toilet training, or infertility (if meatus severely proximal); risk of urethral stricture or fistula post-repair
• Epispadias: dorsal placement of urethral meatus; often associated with exstrophy complex; functional significance depends on severity
• Micropenis: penile length <2.5 cm at term; reflects insufficient androgen exposure in utero; associated with hypogonadism or developmental disorders
• Congenital penile curvature: developmental deformity distinguished from Peyronie disease by congenital onset and stability over time

Histopathologic Evaluation

• Biopsy technique: punch or excisional biopsy of suspicious lesions; ensures adequate sampling of dermis and subcutis to assess invasion depth
• Penile SCC histology:
• Malignant squamous epithelium with varying differentiation
• Invasion into dermis and deeper structures defines invasiveness
• Mitotic figures and necrosis indicate high-grade lesions
• Depth of invasion (Breslow thickness or TNM staging) prognostically significant; invasion into corpora cavernosa indicates advanced disease (T3)
• Perineural invasion and angiolymphatic invasion adversely affect prognosis
• Surgical margins must be confirmed free of tumor
• PeIN/VIN histology: full-thickness atypia with hyperkeratosis/parakeratosis; HPV in situ hybridization positive in HPV-associated cases; lacks invasion through basement membrane (distinguishing feature from SCC)
• Lichen sclerosus: hyalinized sclerotic zone in superficial dermis, vacuolar degeneration of basal layer, dense T-lymphocytic infiltrate with sparse rete pegs; absence of mucin deposition (distinguishes from morphea)
• Lichen planus: band-like lymphocytic infiltrate at dermoepidermal junction (lichenoid), saw-tooth pattern of epithelium, colloid bodies (Civatte bodies) at junction, basal cell apoptosis
• Melanoma: increased mitotic rate (>1 per mm²), cytologic atypia, irregular nesting and asymmetry, ulceration, deep invasion; Clark level and Breslow thickness correlate with prognosis

Gross Pathology

• Penile SCC: infiltrative, ulcerative lesion often with rolled borders and granulation tissue base; may be exophytic and fungating; color typically tan-white with areas of necrosis; size variable but often <4 cm at diagnosis; specimen includes tumor, margins, and regional lymph nodes
• Peyronie disease plaque: firm, whitish-gray, fibrotic tissue in tunica albuginea; may contain calcium or ossification in chronic phase; no necrosis or significant inflammation in established lesions
• Lichen sclerosus lesion: white, atrophic patch with thin, wrinkled ("cigarette paper") surface; no ulceration in early disease; progressive cases show scarring with contracture
• Melanoma: irregular, pigmented lesion with color variation (blue, brown, black); may be ulcerated; size often >6 mm at diagnosis

Laboratory and Imaging Studies

• Penile SCC:
• HPV genotyping by PCR/in situ hybridization: HPV-16/18 detected in 70-90% of basaloid/warty SCC; prognostic significance unclear but HPV-positive tumors may be more chemosensitive
• **p53

Emergencies first

• Ischemic priapism: per the AUA/SMSNA priapism guideline, confirm with corporal blood gas (ischemic pattern: pO2 <30 mmHg, pCO2 >60 mmHg, pH <7.25), then perform corporal aspiration with saline irrigation plus intracavernosal alpha-1 agonist (phenylephrine, dilute 100–500 mcg every ~5 minutes with blood pressure monitoring) to restore sympathetic-mediated cavernosal smooth muscle contraction. Refractory cases proceed to distal (Winter, Ebbehoj, Al-Ghorab) then proximal shunting; early prosthesis is considered after prolonged episodes. Sickle cell disease requires hydration, oxygen, analgesia — but these adjuncts must not delay aspiration. Non-ischemic priapism is managed conservatively or with selective arterial embolization, not with phenylephrine.
• Paraphimosis: manual compression of glans edema and reduction; dorsal slit if reduction fails. Fournier gangrene: emergent surgical debridement plus broad-spectrum antibiotics (e.g., piperacillin-tazobactam with vancomycin, vancomycin dosed to a 24-hour AUC/MIC of 400–600 per the 2020 IDSA/ASHP consensus).

Infectious and inflammatory disease (CDC STI Treatment Guidelines)

• Syphilitic chancre: benzathine penicillin G 2.4 million units IM once. Chancroid: azithromycin or ceftriaxone. HSV: nucleoside analogue (valacyclovir). Candidal balanitis: topical azole (clotrimazole) with glycemic control.
• Lichen sclerosus: ultrapotent topical corticosteroid (clobetasol) is first line; circumcision is often definitive; meatotomy/urethroplasty for stricture.

Emergencies (flagged)

• Ischemic priapism (emergency): compartment-like cavernosal ischemia → smooth muscle necrosis and corporal fibrosis; signalled by a rigid, exquisitely painful erection with soft glans and acidotic corporal blood gas. Duration beyond roughly a day predicts irreversible erectile dysfunction and penile shortening.
• Paraphimosis (emergency): retracted phimotic ring acts as a venous tourniquet → glans edema, then arterial compromise and necrosis; signalled by a painful, swollen glans with a constricting proximal band.
• Fournier gangrene (emergency): polymicrobial necrotizing fasciitis of perineal fascia, favored by diabetes and immunosuppression; signalled by pain out of proportion, crepitus, dusky skin, and systemic toxicity.

Disease-related

• Malignant transformation: chronic inflammation in lichen sclerosus and long-standing phimosis drives p53-mutant differentiated SCC; signalled by a non-healing ulcer, induration, or bleeding within a white atrophic plaque — biopsy, do not treat empirically.
• Urethral stricture and meatal stenosis: periurethral sclerosis in lichen sclerosus; signalled by spraying stream, straining, post-void dribbling, and eventually obstructive uropathy.
• Inguinal nodal metastasis: rich bilateral lymphatic drainage of the penis; signalled by fixed, matted nodes and skin ulceration with risk of femoral vessel erosion.
• Peyronie sequelae: plaque contracture producing curvature, hourglass narrowing, shortening, penetration failure, and depression.

Treatment-related

• Collagenase injection: enzymatic weakening of tunica albuginea → corporal rupture/penile fracture (audible pop, detumescence, hematoma) — urgent urologic evaluation; more often benign penile ecchymosis.
• Intracavernosal alprostadil or phenylephrine failure: iatrogenic priapism; phenylephrine may cause hypertension, reflex bradycardia, and arrhythmia.
• PDE-5 inhibitors: profound hypotension with nitrates; also headache, visual color-tinge (PDE-6 cross-inhibition), and rare non-arteritic anterior ischemic optic neuropathy.
• Inguinal lymphadenectomy: disrupted lymphatics → chronic lymphedema, lymphocele, wound dehiscence, and skin-flap necrosis.
• Penectomy/urethrostomy: meatal stenosis, urinary spraying, and major psychosexual morbidity.
• Cisplatin-based chemotherapy: nephrotoxicity, ototoxicity, neuropathy.
• Circumcision: bleeding, infection, and later meatal stenosis from ammoniacal dermatitis of the exposed meatus.

• Ulcer triage is the classic stem: painless, indurated, clean-based solitary ulcer with rolled borders = syphilitic chancre; multiple painful, purulent, ragged ulcers with suppurative buboes = chancroid; grouped vesicles on an erythematous base = HSV. Painless equals Treponema; painful equals ducreyi — the pain question is the discriminator examiners lean on.
• HPV serotype pairing: 6 and 11 cause condyloma acuminatum (benign, koilocytes, no invasion); 16 and 18 drive basaloid/warty SCC and PeIN through E6/E7 inactivation of p53 and Rb. The common distractor is calling a giant condyloma (Buschke-Löwenstein) an invasive SCC — it is locally destructive but rarely metastasizes.
• PeIN eponyms: erythroplasia of Queyrat = carcinoma in situ on the glans (red velvety plaque); Bowen disease = in situ on the shaft; bowenoid papulosis = multiple HPV-related papules in younger men that often regress.
• Single best next step for any persistent penile lesion is biopsy, not empiric antifungal or antibiotic therapy — chronic "balanitis" that will not clear is SCC until proven otherwise.
• Priapism: the tested next step in a sickle cell patient with a painful erection is corporal blood gas, then aspiration/irrigation with intracavernosal phenylephrine per the AUA/SMSNA guideline — not transfusion or observation. A painless, non-fully-rigid erection after perineal straddle trauma is high-flow priapism and is not an emergency.
• Peyronie disease = dorsal fibrotic plaque of tunica albuginea with curvature, classically linked to Dupuytren contracture (and plantar fibromatosis). Treat only in the stable phase; surgery during the active inflammatory phase risks recurrence.
• Lichen sclerosus (BXO): white cigarette-paper atrophic plaques; first line is ultrapotent topical clobetasol; long-term risk is differentiated, HPV-negative SCC.
• Hypospadias: do not circumcise the newborn — the foreskin is needed for surgical repair.