Perineum

The perineum is the area referring to the shallow internal compartment and external surface of the body (Fig. 11.11.1.1).

The compartmental area of perineum is seen inferior to the pelvic outlet and is divided from the main pelvic cavity by the pelvic diaphragm.

This pelvic diaphragm holds up the urogenital and gastrointestinal systems and plays an important role in defecation, micturition, sexual intercourse and labour.

Extent and boundaries of perineum

When viewed in subject with abducted thighs, the perineum resembles a diamond-shaped area that is bounded by the mons pubis anteriorly, medial aspect of the thighs laterally and the gluteal folds and upper end of natal cleft posteriorly and following osseofibrous boundaries:

Division of perineum (Fig. 11.11.1.2)

An imaginary transverse line connecting the anterior ends of the ischial tuberosities splits the perineum into two triangles:

Urogenital triangle

The urogenital triangle is the front half of the perineum. It is bounded by pubic symphysis, ischiopubic rami, and an imaginary line between the two ischial tuberosities.

Urogenital triangle has number of fascial layers and pouches and complex.

Dissimilar to the anal triangle, the urogenital triangle has an extra layer of strong deep fascia, which is called as perineal membrane. The membrane has pouches on the superior as well as inferior surfaces (Fig. 11.11.1.3).

The layers of the triangle (deep to superficial) (Fig. 11.11.1.4):

• • Deep perineal pouch – bounded by the perineal membrane in the inferior aspect and deep fascia of pelvic floor in the superior aspect. It contains some part of the urethra, external urethral sphincter, and vagina in females, bulbourethral glands and the deep transverse perinei muscles in males.
  
• • Perineal membrane – Tough fascia, which is perforated by urethra and vagina in females. It provides attachment for the muscles of the external genitalia.
  
• • Superficial perineal pouch – is a space between the perineal membranes in the superior aspect and the superficial perineal fascia in the inferior aspect.
  
  
  

  
  
  • Contents: Tissues that form the penis and clitoris, ischiocavernosus, bulbospongiosus and superficial transverse perineal muscles.
    
  • The Bartholin’s glands are seen in the superficial perineal pouch.
  
  
• • Perineal fascia is the continuity of the abdominal fascia (Fig. 11.11.1.5). It has two fascial components:
  
  
  

  
  
  • Deep investing fascia, which is called as Gallaider’s fascia, covers the superficial perineal muscles, the penis and the clitoris.
    
  • Superficial fascia has two layers.
    
  • Superficial layer – which is continuous with Camper’s fascia of the anterior abdominal wall. It is replaced with dartos muscle in scrotum.
  
  
• • Deep membranous layer is called as Colles’ fascia, which is continuous with Scarpa’s fascia of the anterior abdominal wall.

Perineal body

Is located on the midpoint of theoretical transverse line joining the ischial tuberosities that is providing attachment to the perineal muscles.

Perineal body lies deep to skin and subcutaneous tissue in the midline at the junction of anal and urogenital triangles. It is seen behind the vestibule of the vagina or bulb of the penis. Anus and anal canal are seen behind the perineal body. The perineal body is varying in size with little fat deep to the overlying skin (Fig. 11.11.1.6).

All the perineal muscles converge in the perineal body and have three stratum.

Superficial stratum includes bulbospongiosus, superficial transverse perenei muscles and superficial part of external anal sphincter.

Intermediate stratum includes sphincter urethrae and deep transverse perenei muscle and deep part of the external anal sphincter.

Deep stratum contains levator ani muscle.

Perineal membrane and urogenital diaphragm

It is a triangle-shaped musculofascial diaphragm situated in anterior half of the perineum located in the region of the urogenital triangle filling space of pubic arch.

It is pierced by urethra in both male and female and vagina in females.

It holds the prostate gland and it constricts the vagina.

It has:

Blood supply and lymphatics

The superficial perineal space receives its blood supply from the internal pudendal artery, which is the branch of the internal iliac artery.

Nerves

Pudendal nerve and its branches are supplying the superficial perineal space.

The posterior labial nerve, which is a branch of pudendal nerve has a medial and lateral branch and runs along the lateral part of the urethral triangle to supply the skin of the labia majora.

The posterior scrotal nerve, which is branch of pudendal nerve has a medial and lateral branch and runs along the lateral part of the urethral triangle to innervate the skin of the scrotum.

FG usually not only involves the corpora, urethra, testes, cord structures and deep muscular structures, but also the superficial and deep fascia as well as the skin.

The infection spreads along the anatomical fascial planes. So knowing the routes of spread, familiarity with the perineal anatomy and its fascial planes is very important in understanding the potential pathways of disease spread. Thus if the Colles’ fascia is interrupted, then the infection can easily spread to the ischiorectal fossa and subsequently to buttocks and thighs.

Aetiology

Pathogenesis

In FG, rotting bacterial infection can cause microthrombosis of small subcutaneous vessels bringing about gangrene of the overlying skin.

Cultures of FG wound often show poly microbial infections by aerobes and anaerobes, which include:

Comorbid risk factors for FG

Clinical presentation

Nonuniformity in clinical presentation. From subtle onset and slow progression to swift onset and fulminant course. Symptoms of FG include scrotal oedema, hyperemia, fever, pain, pruritus and crepitus. Crepitus is a common feature because of the presence of gas under the skin. Air in the soft tissues is produced by anaerobic bacteria and consists primarily of nitrogen, hydrogen, nitrous oxide and hydrogen sulphide.

FG infection starts as cellulitis then necrotic patches start appearing over the skin and progress to extensive necrosis.

Leucocytosis, anaemia, thrombocytopenia, dehydration, tachycardia, hypocalcaemia, and hyperglycaemia are the systemic manifestations of FG.

FG can rapidly progress to septicaemia and multiple organ failure.

Involvement of the testis is very rare, which suggests retroperitoneal origin or spread of infection.

Differential diagnosis

Investigations

Radiologic features

The diagnosis of FG is usually clinical.

Imaging has an ancillary role. Radiologic evaluation is indicated when the diagnosis is not clearly established.

The goals of radiologic evaluation are:

Plain X-ray

Radiolucent soft tissue gas shadow may be seen over the scrotal or perineal region. The subcutaneous air pockets can enter from scrotum and perineum to the anterior abdominal wall, inguinal regions and thighs. Soft tissue air pocket visualized on X-ray of diabetic patients with FG in 100% of the cases, while physical examination can pick up scrotal wall air pockets only in 29% of the cases.

Ultrasound

High-resolution linear transducer (5–15 MHz) imaging of scrotum is a helpful tool in the diagnosis of FG prior to the clinical suspicious or physical examination of the disease. Ultrasound scan can show widespread abnormalities of scrotum such as scrotal wall oedema/cellulitis, testicular torsion, acute epididymo-orchitis, testicular trauma, necrotizing fasciitis and an obstructed inguinoscrotal hernia. Ultrasound can also display a thickened oedematous scrotal wall, air shadows within the scrotal wall, paratesticular fluid collection.

Presence of subcutaneous air pockets in the scrotal wall with unhealthy echogenic white after shadows is the sonographic hallmark of FG. This distinct sonographic appearance of scrotal wall air shadows is due to fluid–air interface. Often the testis and epididymis are normal in size and echotexture because of different blood supply directly from abdominal aorta through testicular arteries. An obstructed inguinoscrotal hernia may show the presence of air shadows within the bowel loops or within the scrotal sac but not in scrotal wall layers.

Many times ultrasound scan depicts the presence of air pockets in nearby subcutaneous soft tissues other than scrotal wall before physical examination does. Distribution of soft tissue air pocket may indicate the extent of the disease in multiple fascial planes. Scrotal wall emphysema may extend into the perineum, inguinal region and abdominal wall and occasionally into the thigh. Absence of scrotal wall emphysema dose not excludes the diagnosis of FG.

CT scan

CT is a very valuable tool in diagnosing and determining the extent of FG. Clear knowledge of the anatomy of perineal region and fascial planes, the extent of the disease can be established to a degree more specific than is possible with physical examination/sonography.

CT is the modality of choice in FG. CT findings include:

CT scan dominates in the detection of deep-seated perineal, pelvic and intraabdominal fluid collections, which is very important in the eradication of the disease. It also provides wide field of view of perineum, pelvis and proximal portion of the lower extremities. Retroperitoneal extension is also well demonstrated with CT. Extent into anal triangle and urogenital triangle can be clearly made out.

CT screening of perineum and pelvis can frequently show the underlying cause of the FG such as urethral pathology, perianal abscess, fistulous tracts, incarcerated hernia and source of infection that may be from intraabdominal or deep pelvic process and helping to planning of surgical debridement and management.

Posttreatment follow-up CT scan is very important in assessing for improvement or worsening of FG. CT is useful in deciding additional therapy or surgical excision.

MRI scan

MRI scan of the pelvis and perineal region is used to assess the extent of FG along the tissue planes. MRI yields better soft tissue details than the CT scan (Fig. 11.11.1.8).

STIR imaging displays the oedema/inflammation of skin, subcutaneous fat and inter muscular planes as hyperintense shadows.

Air loculi present in interstices of scrotal wall appear as hypointensities.

MRI scan clearly demonstrates the extension of FG inflammatory process into the inguinal canal, pelvic cavity and in ischiorectal fossa as bright hyperintense shadows.

Prolonged time for MRI scan, patient monitoring difficulties, clinically unstable patients limit the practical usefulness of MRI scan.

Treatment

Complications

Treatment outcome

The mortality in FG is little high ranging from 3% to 45%.

Factors associated with high mortality include:

Prognosis

Early presentation in good functional status along with appropriate and timely treatment leads to a good outcome.

FG wound extending more than 5% of the body surface area carries a poor prognosis. Abdominal wall or lower limb involvement has notable increase in mortality rate.

New prognostic criteria for fournier’s gangrene

Prevention