Fournier’s Gangrene complicated by development of an ano-scrotal fistula

A 60 year-old male presented with a history of diarrhoea. Clinical examination demonstrated sepsis and inferior scrotal and perineal necrotising fasciitis, in keeping with Fournier’s gangrene. This was treated with emergency surgical debridement. Post-operative outpatient recovery was complicated by a chronically discharging sinus in the anterior midline of his scrotum.

Routine perianal sepsis protocol MRI with IV Gadolinium performed.

Trans-sphincteric fistula arising anteriorly with mucosal defect at 12 o’clock in the upper anal canal. After extending antero-inferiorly, it bifurcates into two parallel fistulous tracts in the posterior perineum. These continue anteriorly before converging in the posterior scrotum to form a single tract to the anterior scrotal surface. T1 fat-saturated post-gadolinium sequence demonstrates peripheral enhancement of the tracts, identifying them separately from the non-rim enhancing corpus cavernosa (Figures 1 and 2). Fat-saturated sequences without enhancement demonstrate similar appearance of the tracts to corpus cavernosa, although do delineate the tracts from surrounding fat (Figure 3). Wide field-of-view T2 images demonstrate extension from anus to the anterior scrotal dermal surface (Figures 4 and 5).

Ano-scrotal fistulas represent a rare pathology, mostly seen in a paediatric population as a congenital phenomenon.[1] To our knowledge, no cases have been described in adults as a complication of Fournier’s gangrene (FG).

FG is a rare form of necrotising fasciitis affecting the perineal and genital region. Pathogenesis often from a combined aerobic and anaerobic polymicrobe insulting the fascia through various processes, including; urinary tract infections, perianal abscess, surgical procedures and trauma. Risk factors include; male gender, diabetes mellitus, hypertension, malignancy and alcohol abuse.[2] As a life-threatening, urological emergency, the Fournier’s Gangrene Severity Index was developed to predict prognosis, taking into account vital signs and haematological/ biochemical markers.[3]

Although traditionally a clinical diagnosis, imaging can aid assessment, particularly in absence of physical findings. Ultrasonography may demonstrate a thickened, oedematous scrotum/ perineum with hyperechoic, hyper-reflecting, ring-downing foci (gas) within the wall.[4]

Where ultrasound is equivocal, CT is recommended and may clarify extent of fascial involvement preoperatively.[4] McGillicuddy et al. proposed a CT-based scoring system for necrotizing soft tissue infections assessing for fascial air, muscle/ fascial oedema, fluid tracking, lymphadenopathy and subcutaneous oedema.[5]

Due to longer acquisition time, MRI is not advised as an initial modality but can assess for residual disease post-operatively.[4]

Gastrointestinal fistulas are epithelialized tracts between the gastrointestinal lumen and another organ. Aetiologies include congenital malformations, trauma, tumour, or because of infection and inflammation.[6]

In this case, the parallel nature of the fistulous tracts could be mistaken for corpus cavernosa. A combination of fluid-sensitive and fat-suppressed T1 Gadolinium techniques are useful to identify these fistulous tracts from normal structures.[7]

De Miguel et al.’s, published by Radiographics 2011, suggested protocol in the evaluation of perianal fistulas includes a combination of fat-supressed techniques with Gadolinium and “obliquing” the axial and coronal planes to allow a truer assessment of the anal sphincter complex.[8] Fat-suppressed T2 turbo spin echo (TSE) provides higher structural delineation than STIR.[7,8] In the early postoperative stage a non-enhanced fat-saturated T1 sequence may help rule out postoperative haemorrhage.[7] Use of diffusion-weighted sequences has been reported in conjugation with T2 sequences given inflammations ability to limit water mobility and may be of particular value in patients not suitable for Gadolinium.[8,9,10] When reporting perianal fistulous disease it is important to clarify for the referring surgeon the presence and number of fistulous tracts, type, path and degree of complexity.[10]

Written informed patient consent for publication has been obtained.