Psoas Abscess: Definition and Management

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You have certainly heard of the psoas tendonitis, one of the most common pelvic diseases affecting the psoas muscle. Athletes certainly have an idea! But did you know that this muscle can also be the site of suppuration? It's called thepsoas abscess. What is it about ? Is that bad ? Is it a curable disease? Answers in this article.

Anatomical reminder of the iliopsoas muscle

Le iliopsoas muscle, also called iliopsoas, is a deep muscle forming part of the muscles forming the pelvic girdle. It is a paired and symmetrical muscle which originates on either side of the spine (lumbar) and fits on the thigh, more precisely on the upper end of the femoral bone.

It is called iliopsoas because it is made up of two muscle heads: the psoas major which originates from lumbar spine and iliac muscle which arises from the iliac fossa. The two meet at the groin to fit over the upper end of the femur.

It is thanks to the perfect anatomical position of this muscle that we can flex the thigh on the pelvis. It allows complete flexion of the pelvis if the contraction is bilateral, and homo or contralateral tilt if the contraction is unilateral.

On the other hand, the fact that a significant part of the femoral nerve crosses the psoas muscle, its impairment constitutes a determining factor in the triggering of cruralgia.

Psoas abscess: what is it?

THEpsoas abscess is an infectious disease characterized by suppuration ou collection of pus at the level of the psoas muscle or iliopsoas. It is categorized into primary abscess psoas (resulting from the spread of an infectious agent by hematogenous or lymphatic route), and secondary abscess psoas (caused by contiguous spread from an adjacent focus of infection).

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In the literature, psoas abscess is most often secondary. The most common causes are gastrointestinal or musculoskeletal infections.

Causes of psoas abscess 

The psoas abscess is usually of infectious origin and the etiologies of a primary abscess are different from those of a secondary abscess.

As for the primary abscess of the psoas, it could be that it occurs following a propagation via the blood or the lymph of a pathogenic germ. It can also be caused by a local muscle injury, namely trauma (direct impact on the lower back) or ischemia.

The secondary abscess, which is the most common in the literature, occurs by contiguity, when an infection affects one of the neighboring organs. It could be one of these cases:

  • Spondylodiscitis complicated (inflammation of the bodies and intervertebral discs)
  • Complication of a urinary tract infection
  • Digestive infection such as diverticulitis
  • Complication of appendicitis or appendectomy
  • Crohn's disease (IBD)
  • Arthritis or osteomyelitis
  • Complication of tuberculosis (Pott's disease)
  • Infected lymph nodes

The germs most often involved are:

  • Pathogenic Staphylococcus ou aureus : generally responsible for an osteo-articular infectious site.
  • coli. Or E.coli : 2nd most common cause. Most often associated with a gastrointestinal or urinary focus.
  • Bacteroide (spp, s.viridans): frequently isolated from a focus of gastrointestinal origin.
  • Mycobacterium tuberculosis: causative agent of tuberculosis and tuberculous forms of psoas abscess. This is the prerogative of immunocompromised subjects.

How does a psoas abscess manifest?

The deep anatomical location of the iliopsoas muscle makes its impairment very difficult to recognize. Apart from the infectious syndrome, the abscess results in non-specific signs and constitutes a diagnostic trap for the clinician.

The infectious symptoms are varied, and can be:

  • A fever
  • Personalized lumbar or iliac pain: permanent and sometimes throbbing, which worsens during the movements
  • Un Psoitis: which corresponds to an inflammation or tendonitis of the psoas causing a painful flexion of the thigh.
  • A hip external rotation related to the attack of its musculature by contiguity
  • A painful palpable mass in the lower abdomen
  • Signs that may point to the conditions in question (appendicitis, tuberculosis, IBD, urinary tract infection, etc.)
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Diagnosis of psoas abscess 

Admittedly, the abscess of the psoas is difficult to recognize because of its not very specific signs, but its diagnosis is facilitated, today, thanks to new techniques ofmedical imaging (MRI, CT, ultrasound).

Abdominopelvic ultrasound is generally requested for the positive and etiological diagnosis of the abscess (sensitivity 80%).

La CT (scanner) and l'IRM make it possible to make the positive diagnosis of the abscess for their sensitivity approaching 100%. They are also used to specify the extension of the abscess and detect underlying damage.

Complete diagnosis also requires biological and microbiological proof of the presence of the infection. The biological assessment includes:

  • Personalized inflammatory markers (elevated leukocytes, inflammatory anemia, CRPEtc.).
  • Creatine Kinase CK high: muscle-specific enzymes
  • blood culture or blood culture that needs to be started at thermal peak
  • PCR microbiological test for germ isolation

Psoas abscess: what consequences?

In the absence of adequate treatment, the abscess of the psoas evolves towards the occurrence of complications that may involve the functional prognosis. They can be observed immediately or in the long term.

The suppuration can extend towards the abdominal cavity and cause, among other things, a peritonitis (inflammation of the peritoneum). The extension can also be done towards the pelvic organs in particular the urinary and genital systems.

In the extreme, the responsible germ can invade the bloodstream and cause a Sepsis ou sepsis (generalized infection), the severity of which can compromise the vital prognosis of the patient.

How to manage a psoas abscess?

The treatment of psoas abscess is essentially based on two therapeutic components:

  • Antibiotic therapy
  • Drainage of the abscess

The antibiotics to be prescribed must ensure coverage of the most incriminated germs: S.aureus and E.coli.

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Usually, we use the beta-lactams (Ampicillin or Piperacillin), Metronidazole ou 3rd generation cephalosporin (ceftriaxone).

The duration of treatment is usually 4 to 8 weeks.

Note : It is necessary to underline the importance of the association of these two types of treatment, because the use of antibiotics alone is not enough and has never led to the total healing of the abscess.

Antibiotic therapy should be followed by abscess drainage. This is indicated for draining an abscess of at least 3,5cm.

Technically, drainage is done under imaging guidance (preferably CT), and consists of draining the pus by accessing the muscle via the retroperitoneal route. A drain catheter can be left in the abscess cavity for possible additional drainage.

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