EPIDEMIOLOGY:

The clinical features of the 5 patients included in this study are summarized in Table 1.

FG is a rare condition, although its incidence is increasing due to an ageing population and a higher prevalence of diabetes.

Most patients described in the literature are men in their sixth and seventh decade, in our study the average age was 67 years (range 58-80).

 Concomitant illnesses are associated in 90% of the cases, such as diabetes (40-60%) [1] alcoholism, obesity and immune-compromised conditions (HIV, lymphoproliferative disorders, cytotoxic drugs, radiotherapy, chronic steroid abuse). In our patients, alcoholism was the most frequent concomitant condition (3/5), followed by diabetes type II (2/5), morbid obesity (1/5) and sigmoid cancer (1/5). 

PHYSIOPATHOLOGY:

The physiopathology of FG involves polymicrobial aerobic and anaerobic bacteria normally present in the pelvic area (perineum and genitalia). Streptococci and enterobacteria are reported to be the most common isolated bacteria in the literature. [2]

Bacterial wound cultures from our 5 patients showed polymicrobial flora with both aerobic and anaerobic bacteria. The species commonly identified were predominantly facultative anaerobic organisms, such as Staphylococcus, Streptococcus, Enterococcus genus (gram-positive bacteria) and Klebsiella, Proteus and Escherichia coli genus (gram-negative bacteria). Less frequently observed were anaerobic bacteria like Bacteroides genus (gram-negative bacteria). Candida albicans was identified in only one patient. Table 2 

The synergistic activity of bacteria leads to obliterative endarteritis, microthromosis of the subcutaneous vessels and consequently necrosis of the surrounding tissues that spreads across the fascial planes of the perineum.

Perineum fascias include Colles, Dartos, and Scarpa fascias which are in continuity with each other, allowing infections to spread rapidly [3].  Table 3

CLINICAL MANIFESTATIONS [4]

The clinical presentation of FG can be diverse depending on the stage of the infection.

At the beginning of the infection, there is typically painful swelling, tenderness, erythema of the scrotum or perineum, which can mimic mild infections such as erysipelas and cellulitis Table 4. This early stage was seen in three of our patients. However, even in an early stage, the presence of severe pain, disproportional to the clinical examination, should raise the suspicion to the clinician of necrotizing fasciitis. Since the necrotizing fasciitis spreads along the fascial planes, the superficial skin is spared from the infection at the beginning, making the extent of the disease difficult to visualize.

As the fasciitis progresses, small cutaneous necrotic areas can appear (bullae, blisters, skin necrosis, which are not frequently seen in cellulitis or erysipela) with surrounding erythema and oedema as well as crepitus on palpation, which was seen in only in one of our patients. At this point, necrotic inflammation spreads quickly (as fast as 2-5cm an hour), spreading through the fascial planes and extending into the surrounding areas (perineum, scrotum, hypogastrium), leading to rapid deterioration of the patient’s clinical status, which was the symptom of one patient.  

Immediate surgical debridement of inviable tissue should be carried out within the first 24 hours. Empiric broad-spectrum parenteral antibiotic treatment is required as well as stabilizing medical parameters. Even with a proper treatment, it’s a highly morbid and surgically emergent condition, with potential mortality between 15 and 50%. In our case series, two patients died due to multiple organ failure secondary to the progression of necrotizing fasciitis, consistent with the mortality rate decribed in the literature.

GENERAL IMAGING FINDINGS: [5,6,7]

Diagnosis of FG is often made upon physical examination, clinical findings and medical history. Nevertheless, CT was performed in all of our cases because it allows us to confirm the diagnosis, accurately assess the extent of the necrosis, which is important for surgery planning and, in some cases, contributes to elucidate the triggering cause. It also contributes to evaluate the response to treatment.

Imaging plays an important role in the management of selected cases when the diagnosis of Fournier gangrene is uncertain. However, urgent surgical intervention should not be delayed by unnecessary radiological studies.

The following are common imaging findings in our patients with FG: 

Plain abdominal X-ray: 

• Subcutaneous emphysema extending from the perineum and external genitalia to the inguinal regions, thigh and anterior abdominal wall (although the presence of air is not pathognomonic, it increases the suspicion).  Fig. 1,  Fig. 2

Ultrasonography [12]: 

• The key imaging finding is subcutaneous gas, which appears on ultrasound as multiple echogenic reflectors (reverberation artefact) in the subcutaneous tissues with dirty shadowing in the perineal regions. Fig. 3
• Useful in differentiating a soft tissue necrotizing infection from other scrotal pathology. Testicular blood supply is preserved due to the retroperitoneal blood supply from the aorta.

Computer Tomography (CT) [8,9]: 

CT is the imaging modality of choice for FG given its short acquisition time. Its main findings are:

• Subcutaneous emphysema in the genital area Fig. 4 
• Stranding of the fat, soft tissue thickening or intramuscular oedema
• Fascial thickening which can enhance after contrast. A normal fascia excludes fasciitis [4]
• Dissecting gas along fascial planes in the absence of penetrating trauma (including iatrogenic) is essentially pathognomonic of FG [4] which was present in all our patients. Fig. 5
• Abscesses and collections are less frequent and was only seen in one patient.Fig. 10,  Fig. 12 

Magnetic Resonance Imaging (MRI):

 Even though it is an excellent modality to evaluate in detail soft tissues, it plays a limited role due to the cost and the longer scan time. It could be performed for selected patients that are clinically stable and cooperative. It can also help to define para-rectal involvement, suggesting the need for bowel diversion or to precisely asses the extension of the disease [10]. Some argue that MRI is even more helpful than CT in planning surgery because it shows more accurately the extent of the necrosis and that it should be used in the early diagnosis of this disease [11]. However, MRI has a limited availability in emergency departments of most hospitals.