Pilonidal Sinus Disease (Pilonidal Cyst)

Are You Confident of the Diagnosis?

The development of a pilonidal cyst or pilonidal sinus disease (PSD) most commonly occurs along the upper portion of the gluteal cleft, especially when there is an extraneous congenital invagination or sinus tract near the apex of the natal crease (Figure 1 ). This epithelial invagination functions as a funnel-like structure, shunting hair down into the depths of its cul-de-sac as a consequence of different body movements.

Figure 1.

Body hair that sheds naturally can migrate over the surface of the skin in the vicinity of the lower back and buttocks and travel downward into the congenital epithelial invagination of a pilonidal (Latin: pilus = hair and nidus = nest) sinus until it reaches the depth of its apex. When the fragments of hair shafts eventually burrow through the epithelial barrier at the base of the sinus tract because of repetitive and rhythmical body movements, a foreign body reaction is produced, generating an inflammatory and granulomatous response. This is perceived as an abscess at the base of the spine along the upper pole of the gluteal cleft (Figure 2).

Figure 2.

Because of the proximity to perianal flora, colonization with gastrointestinal organisms frequently occurs, intensifying the inflammatory reaction and resulting in suppuration. Without appropriate treatment PSD abscesses will persist, expand and rupture, extending their purulence centrifugally and creating additional epithelial tracts beyond the confines of the original pilonidal sinus.

Similar pilonidal sinus tracts with foreign body granulomatous abscesses have been reported at the base of the interdigital web spaces of barbers, sheep shearers, and dog groomers. In such cases, fragments of cut hair remain trapped in the cutaneous webs at the base of the fingers. Suppuration is minimal because secondary colonization does not frequently occur.

At one time thought to be a congenital disease, PSD is now believed to be an acquired disorder because not everyone with a pilonidal sinus will develop PSD. Only those whose body hair has burrowed deep into the pilonidal sinus and breached the cutaneous barrier will result in a foreign body reaction. Many can live a lifetime with a pilonidal sinus without PSD, even if they are hirsute. It is coarse, thick hair that will create PSD when it glides over the surface of the lower back and upper buttocks and pierces through the cutaneous barrier at the base of a pilonidal sinus funnel.

Characteristic findings on physical examination

Physical examination reveals a painful, edematous, erythematous inflamed nodule or abscess at the base of the spine that is situated at the upper pole of the gluteal cleft. Occasionally the area is so painful that patients have difficulty sitting or walking. With the slightest amount of external pressure over the area there can be a constant purulent and serosanguinous discharge and soiling of clothing.

Expected results of diagnostic studies

There is no other disorder that can produce such physical findings and no other diagnostic procedures are necessary to make the diagnosis of a pilonidal cyst. A culture of the purulent discharge can be done to identify the incidental aggravating infectious organisms. Many times tufts of hair (comprised of both fragmented and whole shafts of hair) can be seen emanating from the top of the pilonidal sinus orifice.

A pilonidal sinus characteristically is lined with stratified squamous epithelium. They can even appear with multiple orifices. Microscopically, one can observe in active PSD chronic granulation tissue containing hairshaft fragements, epithelial debris, neutrophils, lymphocytes and plasma cells and, occasionally, hemosiderin-laden macrophages. Foreign body giant cells and hair fragments along with fibrosis of varying degrees also are frequently seen. Cutaneous appendages are not seen in the walls of the sinus tract. Malignant transformation is rare, but cases of squamous cell carcinoma and verrucous carcinoma have been reported.

Diagnosis confirmation

Other similar types of hair granulomatous disorders should be differentiated from PSD. Hidradenitis suppurativa can also appear as abscesses of hair granuloma. However, they are more frequently found as multiple lesions in the groin, axillae, and submammary area. When lesions of hidradenitis suppurativa appear in the perianal area they are not necessarily confined to the midline of the upper gluteal cleft and usually appear as multiple lesions over a more extended area. Pyoderma gangrenosum can contain fragments of hair in their granulomatous eruptions, but patients are usually more debilitated with underlying active diseases. Lesions of pyoderma gangrenosum are more locally aggressive and ulcerative. Spina bifida is found in young patients with additional anatomical abnormalities.

Spina bifida oculta can be unmasked in a younger or older age group, but is usually associated with some degree of a central nervous system (CNS) or spinal abnormality. An anal fistula and perianal abscess is always associated with an extension of an opening within the anal canal that usually does not involve the midline high above the anal verge. It also can be identified with imaging. However, patients with chronic and recurrent PSD have developed extensive tracking down the gluteal cleft and present as a perianal abscess.

Who is at Risk for Developing this Disease?

Individuals who are most at risk for developing a pilar cyst or PSD are those who are born with an extraneous pilonidal sinus tract (a cutaneous invagination) at the apex of their gluteal cleft. Problematic PSD then occurs when fragments of hair migrate over the surface of the lower back and buttocks, travel downward into this congenital epithelial invagination of the pilonidal sinus, and burrow through the epithelial barrier at the base of the sinus tract.

When hair shaft fragments pierce the skin they act as foreign body material and induce a foreign body granulomatous reaction. Clinically this appears as a cyst or abscess at the base of the spine or at the top of the gluteal cleft. However, not everyone born with a congenital pilonidal sinus will develop a pilonidal cyst or PSD. Although hirsutism is a definite risk factor predisposing individuals to develop PSD, obesity and poor hygiene have been identified as significant but minor risk factors.

What is the Cause of the Disease?

Etiology

Roughly 20-30% of those with a pilonidal sinus will develop PSD. The development of PSD is predicated on some known and unknown factors. Occupation and daily activities play a major role in developing PSD. For example, individuals whose occupation requires sitting during most of the day, like truck drivers and chauffeurs, are at greater risk of developing PSD, especially when there are rhythmical movements while they sit for extended periods of time, even if they have a barely perceptible pilonidal sinus tract and minimal amounts of hair over the surface of their buttocks and lower back. This fact came to light during World War II when Jeep-driver soldiers developed PSD after long hauls of duty. Because of this association, PSD was also known as “Jeep-driver’s bottom.”

Pathophysiology

Gravity and the morphological shape of the pelvis and buttocks also play a significant role in the development of PSD. There is a particular curvature and overall shape of the buttocks that will facilitate the natural shedding and fragmentation of body hair with routine bodily movements. In conjunction with gravity, the migration of these hair fragments is promoted over the skin surface in the direction of the pilonidal sinus orifice.

However, there are hirsute men born with a congenital pilonidal sinus who have thick, coarse hair over their backs and buttocks and never develop PSD when their pilonidal sinus is devoid of hair fragments. On the other hand, there are women born with a congenital pilonidal sinus who have a minimal amount of vellus hair populationg the surface of their buttocks and lower backs and routinely develop PSD when there are fragments of vellus hair protruding from their pilonidal sinus.

More importantly, not all men and women who have pilonidal sinus tracts and hairy backs and buttocks are predestined to develop PSD. It is only those men and women who have a predisposing morphologic shape and curvature of their buttocks and who routinely create rhythmical, shearing movements with their lower backs and buttocks in their occupation and normal daily activities who will develop PSD. It has been suggested that gravity and intergluteal motion together create a type of vacuum that directs loose hair into the funnel of the pilonidal sinus.

Likewise, not all barbers, sheep shearers and dog groomers develop PSD. It is only those barbers and groomers whose finger webspaces have a particular morphological shape that encourages entrapment of cut hair fragments to remain in between the fingers and eventully burrow into the skin by the to and fro motion of their fingers as they cut with scissors who will develop PSD. It has been hypothesized that electrostatic energy is generated during the to and fro motion of cutting with scissors that cause the cut hair to be more adherent to the barber’s skin. Also, barbers, hairdressers and groomers who more regularly and thoroughly wash their hands of all fragments of cut hair from their hands are less likely to develop finger web hair granulomas.

Systemic Implications and Complications

Because this is a localized cutaneous disorder, there are no systemic associated findings, except when there is an acute exacerbation of a foreign body abscess, the patient may develop a fever and attendant malaise and myalgias. There is a reported case of lumbar osteomyelitis associated with an epidural abscess, which proved to be fatal, that developed 3 weeks after surgery for a pilonidal cyst. Malignant transformation is rare, but cases of squamous cell carcinoma and verrucous carcinoma have also been reported. Treatment options are summarized in Table I.