Sacrococcygeal pilonidal sinus disease: MRI role and findings

Clinical History

Young male patient with history of previous pilonidal sinus excision 18 months earlier. Complains of persistent discharge from intergluteal fistulous orifice, particularly after sport activities.
Physical examination excluded signs of local infection along the surgical scar; a residual midline cutaneous orifice including a single hair identifiable 3 cm from the anus.

Imaging Findings

Surgical examination was supplemented with fistula exploration and peroxide-hydrogen injection, and identified communication with a second, more cranial cutaneous orifice. Unenhanced and post-gadolinium MRI was requested to depict the anatomy and stage the recurrent pilonidal sinus disease (PSD). MRI (Figs. 1, 2, 3) showed a midline fluid-filled tubular structure consistent with non-ramified fistulous track coursing through the subcutaneous sacrococcygeal region, measuring approximately 9 cm in maximal length from the distal orifice at the natal cleft to the cranial, wider retrosacral cutaneous opening. Fat suppression allowed visualizing oedematous inflammatory changes of the subcutaneous fat surrounding the fistula. After gadolinium contrast, enhancement consistent with inflammatory activity was seen at the periphery of the recurrent fistula and in the surrounding inflamed fat. Inflammation and fistulas did not involve the levator ani muscles, anal sphincter complex and ischio-anal spaces.
Based on MRI findings, the surgeon opted for wide excision of recurrent PSD.

Discussion

Pilonidal sinus disease (PSD) represents one of the commonest surgical problems among young adults, associated with significant morbidity and impaired quality of life. PSD affects males aged 15 to 30 years much more commonly than women, and becomes rare after age 40. Risk factors include obesity, prolonged sitting, deep natal cleft (NC), excessive body hair, sweating and poor hygiene. Pathogenesis involves chronic infection of hair follicles at the NC, repeated buttock movements causing hair to enter follicles and ultimately foreign body reaction, suppuration and discharge through a midline sinus [1-6].
PSD sometimes manifests acutely with formation of a subcutaneous abscess, but generally causes chronic complaints ranging from asymptomatic pits to painful lesions with bleeding or foul-smelling discharge which may extend towards the sacrococcygeal or ischioanal regions. Disease progression is categorized according to the presence of single (stage I) or multiple (stage II, almost 50% of cases) midline pits without lateral extension, midline pit(s) with lateral extension on one (stage III) or both sides (stage IV); recurrent disease represents a separate group. Clinical diagnosis is usually straightforward but manifestations of complex PSD may overlap with those of fistula-in-ano (FIA) from cryptoglandular anal infection: discrimination is crucial since surgical treatment differs and both entities often recur after inadequate surgery [1-6].
Borrowed from experience with FIA, MRI represents the ideal technique to visualize and classify PSD before surgical exploration. The imaging hallmark includes inflammatory changes at the midline skin and subcutaneous tissue at the NC and adjacent buttocks, at least 2 cm posteriorly to the anus. Inflammation commonly extends cranially to involve the subcutaneous planes abutting the coccyx and sacrum. Single, ramified or multiple tubular fistulous tracks with fluid content may be detected, generally including a midline draining sinus plus possible additional fistulas with or without lateral openings. Peripherally enhancing abscess collections are present in nearly 50% of acute cases. MRI has reported 86% sensitivity and 100% specificity for PSD. Differentiation from FIA relies on absent involvement of the perianal region, intersphincteric space and levator muscles [7, 8].
Conservative measures include shaving and hygiene, laser epilation, fibrin glue or phenol injection. Definitive treatment requires surgery in the large majority of patients, to open and remove the infected sinus and ramifications. However, optimal technique is highly controversial between limited sinusotomy versus wide excision, primary closure versus wound healing by secondary intention. Prolonged healing requiring nursing care and recurrences are common [2-4, 6, 9-11].

Differential Diagnosis List

Final Diagnosis

Recurrent sacrococcygeal pilonidal sinus disease

URL:	https://www.eurorad.org/case/13735
DOI:	10.1594/EURORAD/CASE.13735
ISSN:	1563-4086