SAC Incision: detailed description (diagrams)

2. Opening the subcutaneous tissue and exposure of the Scarpa fascia

The skin and subcutaneous fascia are opened with the cutting function on a monopolar handheld diathermy pencil (see Image step 3). The diathermy settings used are 35:35 (blend and spray). The subcutaneous fatty tissue is divided up to, and including, the Scarpa fascia (also known as Camper’s fascia). 

We use the ‘coagulation’ function on the pencil diathermy device, rather than ‘cutting’ to secure haemostasis and minimise blood loss. Be mindful of the superficial inferior epigastric artery (SIEA: see image step 1), which will be encountered (it arises from the femoral artery below the inguinal ligament) and needs to be coagulated or ligated. This incision can be made with a scalpel if necessary but meticulous haemostasis techniques should be employed to minimise blood loss. 

3. Gradual exposure of the rectus sheath

The three main muscles of anterior abdominal wall contributing to the rectus sheath are the external oblique, internal oblique and the transversalis, which form an aponeurosis bilaterally ending at linea alba in the midline. These aponeuroses form the rectus sheath which enclose the rectus abdominis muscle. The sheaths of the rectus abdominis muscle are continuous with those of its contralateral counterpart. The relatively avascular linea alba lies in between both muscles.

The anterior sheath is progressively opened using curved Robert’s artery forceps and monopolar pencil diathermy. The curved forceps are inserted under the rectus sheath then angled upwards and the tips opened in order to separate the sheath from the underlying muscles and ‘tent’ it superiorly (see Image step 4). The tissue between the open tips of the forceps is then cut with the monopolar diathermy pencil. This allows the sheath to be divided without risking accidental incision of the tissue beneath allowing full exposure of the anterior recti muscles bilaterally. When proceeding lateral to the rectus abdominus muscles, due to the extended curvilinear incision, the operator will encounter the abdominal wall nerves, namely the ilio-hypogastric, ilio-inguinal and genitofemoral nerves (anterior division of T12 to L2). By progressively lifting the sheath off the right and left hemi-recti with the Robert’s forceps, the operating surgeon will reduce the risk of injury to these nerves.

Mobilization of the anterior sheath off the recti muscles

The anterior rectus sheath is then lifted cranially off the recti muscles as a flap. This is done by applying Littlewood’s tissue grasping forceps and Lane’s tissue forceps to the anterior sheath and lifting upwards and cranially to allow a plane to be developed between the muscles and sheath with the monopolar pencil diathermy (see Diagram step 5). The rectus sheath is gradually mobilised cranially with gently traction to the level of the umbilicus. The aim of this step is to achieve adequate surgical exposure of the relatively avascular linea alba in the midline and both anterior recti muscles (laterally). The tissue flap which has been developed should be sufficiently wide and long to facilitate the surgical steps that follow.

Assessing feasibility of exteriorizing the gravid uterus

Once the anterior sheath has been fully mobilised off the recti muscles, the linea alba is divided vertically to the level of the umbilicus. Expansion in this plane is safe due to the avascular nature of the linea alba, which is medial to both rectus abdominus muscles. The operator has to then decide if there is now sufficient access to exteriorise the gravid uterus (see Image step 6). In order to do this the operator’s hand is carefully placed into the peritoneal cavity to gently explore the extent of the uterus, the space around it and the presence of any unexpected posterior or lateral adhesions. Care must be taken to ensure there will be no disruption to the tissues affected by the accreta. Exteriorization is deemed feasible when the incision is wide enough to provide sufficient room to ensure there will not be excessive pressure on the uterus and lateral vasculature (there is pressure required but the operator should not have to ‘fight’ to exteriorise the uterus) and there are no adhesions or abnormal vasculature that may be torn in the process. For a video demonstration of the appropriate pressure see.

Exteriorization of the uterus through the SAC incision 

(being mindful of the deep inferior epigastric arteries)

Before proceeding to exteriorize the uterus, it is important to reconfirm our knowledge of the vascular and nerve supply of the anterior abdominal wall. As exteriorization may potentially cause injury to these. The primary blood vessels (arteries and veins) of the anterolateral abdominal wall are the deep inferior epigastric artery (DIEA) and the transverse segmental arteries. The DIEA arises from the external iliac artery, and lies between the rectus abdominis muscle and its posterior sheath. Whilst the transverse segmental arteries are situated between the internal oblique and transverse muscles. The nerve supply of the abdominal wall arises from ventral branches of the 5th to 12th thoracic nerves and include the iliohypogastric and ilioinguinal nerves. These nerves are directed transversely with a course comparable to the course of the segmental arteries.

When gently grasping the fundal posterior aspect of the gravid uterus and flexing it through the abdominal incision, it is crucial to be mindful of the deep inferior epigastric arteries, which could be traumatised during delivery of the uterus (see Image step 7). Therefore, ensuring that the incision is both high and wide enough to allow relatively easy exteriorisation is vital. We have safely performed this with a well grown fetus at 37 weeks’ gestation. If there is polyhydramnios, ultrasound guided drainage of the amniotic fluid may be helpful to reduce the size of the uterus before attempting exteriorisation.

Management of the PAS

The rest of the delivery and subsequent PAS management is completed according to the SAC technique outlined in this website.

Closure of the posterior sheath and peritoneum

At this point it is important to asess the need for surgical drain insertion. The factors which may influence this decision are the patient BMI, risk of collection or seroma formation or the operator’s intuition about the complexity of the case. Placement of the drain is important and due consideration and care should be given to avoid inadvertent vessel or nerve injury at the point. This is followed by closure of the posterior sheath.

The apex of the incision is located cranially at 12 o’clock, this is secured using a looped suture and the closure is continued in a continuous non-locking fashion until it is closed at its most inferior point caudally, at 6 o’clock. The choice of stitch for closure of this is a number 1 monofilament, absorbable suture (eg. Maxon). Continue with this closure until there is no discernible posterior rectus sheath, at which point it should be tied off.

When the tissue transition to visceral peritoneum becomes evident, this requires closure but a 2-0 absorbable, synthetic, braided suture (e.g. Vicryl) should be used (see Image  step 8). This step ensures re-approximation of the linea alba.

Closure of the anterior sheath

Two looped number 1 monofilament absorbable sutures (eg. Maxon) are used to close the anterior sheath in a transverse curvilinear fashion, which mimics the curvilinear skin incision, from the ASIS on the left to the ASIS on the right. One suture starts from the transverse sheath apex near the left ASIS in a continuous non-locking fashion and advances towards the midline, whilst the second suture starts from the transverse sheath apex near the right ASIS and continues in a continuous non-locking fashion towards the midline. The medial ends of each of the two looped sutures are tied off separately. These ends are then tied together in the centre of the incision giving additional security and strength to the anterior sheath closure. Given the length of the transverse incision using a single suture is ill advised as if it fails, the entire closure will be vulnerable to complete dehiscence.

Evaluation of haemostasis and abdominal closure

The surgeon must remain mindful of haemostasis and coagulate any bleeding points in the fascia and subcutaneous layers (see Image step 9). The subcutaneous tissue is doused in povidone iodine to minimise the risk of infection and the Scapa’s fascia is closed with interrupted sutures buried in the subcutaneous fatty layer using an undyed braided absorbable polyglactin suture on a large needle (e.g. vicryl plus). Finally, the skin is closed using a continuous, subcutaneous technique with an absorbable poliglecaprone 25 suture (e.g. monocryl). The incision is then protected with a self-adhering mesh covered with a sterile, liquid topical skin adhesive (Dermabond Prineo) which removes the need for a dressing and reduces infection risk.