Definition of the Pilonidal Region
The pilonidal region refers to the sacrococcygeal area, specifically the natal cleft (gluteal cleft) and surrounding skin within a 5-6 cm radius from the anus. This region is anatomically distinct and clinically important due to its association with pilonidal disease.
Anatomical Boundaries and Characteristics
The pilonidal region is characterized by:
- Location: In the sacrococcygeal area, above the coccyx
- Boundaries:
- Superior: The flat part of the sacrum
- Inferior: The upper end of the gluteal cleft
- Lateral: Extends approximately 5-6 cm from the midline
Clinical Significance and Differentiation
Distinguishing from Normal Coccygeal Dimples
It's important to differentiate the pilonidal region from the area where innocent coccygeal dimples occur:
- Pilonidal dimples/sinuses: Located on the flat part of the sacrum well above the upper end of the gluteal cleft 1
- Innocent coccygeal dimples: Located more caudally, usually within a centimeter of the coccyx within the gluteal cleft 1
A practical clinical rule for differentiation:
- If you draw an imaginary line between the tops of the two forks of the gluteal cleft, a dimple at or below this line is typically a normal coccygeal dimple, whereas a dimple located above this line is more likely to be a pathological dermal sinus tract 1
Association with Pilonidal Disease
The pilonidal region is the primary site for pilonidal disease, which is characterized by:
- Chronic inflammatory condition involving hair-containing sinuses or cysts 2
- Most commonly affects young adults, with male predominance 2
- Believed to result from hair penetration beneath the skin 2
- Can present as abscesses, draining sinuses, or chronic inflammation 3
Histological Features
Histologically, the pilonidal region contains:
- Terminal hair follicles that can be subject to hyperplasia/hyperkeratosis 4
- Skin appendages including sweat glands and hair follicles
- In cases of pilonidal disease, sinus tracts lined with epithelium and often containing hair shafts 5
Relationship to Other Conditions
The pilonidal region has important associations with other dermatological conditions:
- Hidradenitis suppurativa: Some evidence suggests pilonidal disease may be a localized form of hidradenitis suppurativa 4
- Pilonidal disease prevalence: Found in 1.4% to 2.3% of patients with hidradenitis suppurativa, compared to 0.1% to 0.3% in the general population 1
Clinical Evaluation
When examining the pilonidal region, clinicians should assess for:
- Signs of inflammation or infection
- Presence of sinus tracts or dimples above the gluteal cleft
- Hair protruding from openings
- Purulent drainage or abscess formation 6
Understanding the precise anatomical definition of the pilonidal region is essential for proper diagnosis, treatment planning, and prevention of recurrence in patients with pilonidal disease.