This is a presentation about the pathology of pilonidal sinus, covering its pathophysiology, histology, and the development of secondary carcinoma.

1. Histopathology of
Pilonidal Sinus
Dr. Rawa Muhsin Ali
MBChB, ABHS-APath
The Ninth Fast Track Review

2. Contents
• Overview
• Pathogenesis
• Histology
• Role of pathology
• Differentials
• Malignancy
• Should we examine?

3. Pilonidal Sinus
pilus = hair nidus = nest sinus = pocket

4. •Incidence of 26 per 100,000 population
•Male: female ratio 2-4:1
•Mean age 20
•Most common site is natal cleft
•Risk factors include obesity, prolonged sitting, trauma,
deep cleft, increased hair density, PCOS
Overview

5. • Acquired is favored over congenital
• Gender disparity and onset in adolescence
• Association with occupation (Jeep drivers and
barbers’ hands)
• Similar lesions in other body sites
• Lack of skin appendages and lining epithelium in wall
of sinus despite presence of hair shafts deeply
embedded
• Lack of success of surgical methods
Pathogenesis

6. • Bascom showed the midline pits to be enlarged and
distorted hair follicles
• Gravity and motion may create a vacuum pulling
on the follicles
• Inflammation and debris occlude the mouth of the
follicle
• Further expansion and rupture leads to foreign
body reaction and micro abscesses
• Lateral epithelialized tracts develop from the
abscesses, creating a sinus
Pathogenesis
John Bascom (1925-2013)

7. • Follicular occlusion tetrad: Hidradenitis suppurativa, acne conglobata,
dissecting cellulitis, and pilonidal sinus disease
• Defect in follicular keratinization leading to obstruction of the follicle
• Retinoids to reduce size, activity, and inflammation of sebaceous glands

8. • Karydakis insisted that hair
insertion was the only cause of
pilonidal sinus and not an internal
etiology
• Three factors in hair insertion:
• Invader (loose hair)
• Force (causing insertion)
• Skin (vulnerability)
Pathogenesis

10. •Stretching of natal cleft damages hair follicles and opens a
pore
•Pores collect and embed shed hairs and debris
•Movement and skin tightening create negative pressure
•Hairs are drawn deeper and friction creates the main sinus
•Rupture and secondary infection cause foreign body reaction
and abscess with secondary lateral tracts
Pathogenesis

11. Macroscopy

15. •Hair follicle often not identified
•Tract filled with hair, debris, and granulation tissue
•Tract may be epithelialized, but not the cavity (not a
true cyst)
•Inflammation with foreign body giant cell reaction
•Secondary infection creates abscess which may rupture
Histology

27. •Confirmation of diagnosis
•Perianal abscess
•Anorectal fistula
•Crohn disease
•Exclusion of malignancy
Role of pathology

28. Perianal abscess

29. Anorectal fistula

30. Crohn disease

31. •Same mechanism as Marjolin ulcer
• Chronic inflammation impairs DNA repair mechanisms through
free radicals
•Long-standing and recurrent cases
• Average age and duration higher than usual pilonidal disease
• No carcinoma in 86,333 cases in WWII that were treated early
•Rate of transformation reported from 0.02% to 0.1%
• Underreported and under published
Malignancy

33. • 140 cases in 103 papers from 1900 to 2022
• Mean age 54 years, males 91%
• Squamous cell carcinoma (94.6%), basal cell carcinoma, mixed
• Disease-specific survival rate of 59.8% (5-year) and 53.2% (10-
year)
• Lower survival with higher stage and higher grade
• Recurrence in 46.6%, on average within 15 months
• Worse prognosis than primary squamous cell carcinoma
• Similar to Marjolin ulcer
• Surgery is mainstay (no much role for adjuvant chemoradiotherapy)
Safadi et al paper

34. Outcome of primary vs secondary carcinoma
Primary squamous cell
carcinoma
Secondary squamous cell
carcinoma from pilonidal
disease
3-year survival rate 95.3% 61.7%
5-year survival rate 93.6% 59.8%
10-year survival rate 93.6% 53.2%
Recurrence rate after curative
resection
4.6% 46.6%
Regional metastases at diagnosis 3.7% 8.5%
Distant metastases at diagnosis 0.2% 5.4%

35. Should we examine?

36. Thank You
The Ninth Fast Track Review - Pilonidal Sinus