PSOAS ABSCESS+
REVIEW OF LITERATURE ON ASSOCIATED MENINGITIS
July 12th, 2005
Caleb Hale, MD
History
The original description of an iliopsoas abscess was by Dr. Herman Mynter in 1881. Dr. Mynter is also
famous for being the first attending surgeon to examine President William McKinley after the September
5, 1901 assassination attempt that led to his death. Unfortunately, Mynter gave Matthew Mann, an
OB/GYN, permission to operate on the president after Dr. Roswell Park, an acclaimed general surgeon
was unavailable for the procedure. In the time between Dr. Myter’s first characterization of pyogenic
infection of the psoas muscle, the microbiology of the disease seems to have drastically changed. During
the early 20th century, most cases were attributed to Mycobacteria, specifically tuberculosis. With
improved control of M. tuberculosis infection, the microbiology and epidemiology of psoas abscesses
have changed.
Anatomy of the Psoas
The origin of the psoas muscle is the anterior surface of transverse process of the lateral border of the
vertebral bodies and corresponding intervertebral discs of T12-L5. The psoas inserts into the lesser
trochanter of femur and functions to flex the thigh at the hip and also has minimal action in lateral rotation
and abduction of the thigh. The muscle is enclosed in the psoas fascia that often provides a barrier for
spread of infection and often a clue to the origin of that infection. The blood supply to the psoas includes
rich venous blood in communication with the paravertebral lumbar venous plexus. Inflammation of the
psoas may be elicited by performing a maneuver to identify the psoas sign: Pain on passive extension of
the right thigh. Patient lies on left side. Examiner extends patient's right thigh while applying counter
resistance to the right hip. Increased abdominal pain with this maneuver is considered a positive psoas
sign.
Etiology of Psoas Abscess
There are two general categories of psoas abscess, primary and secondary. In Asia and Africa, nearly all
(99.5%) of psoas abscesses are primary, compared to 61% in the US and Canada, and 19% in Europe.
The differences may be due to variable incidence of specific diseases in ceratin parts of the world, or
variability in w/u of specific etiology. Simply put, primary psoas abscesses are those that have no clear
etiology. Secondary abscesses are a consequence of direct extension of infection from adjacent organs.
 Primary Psoas Abscess: Usually occurs in younger patients with 83% of cases occurring in
patients under 30. There is no predilection for the right or left psoas. They are 3 x more
common in men than women and nearly 90% are caused by Staphylococcus aureus. The
etiology of these abscesses is not well understood, some sources site a possible association
with muscle trauma (major or minor). The thought is that microhematomas may form with
trauma that can become secondarily infected. In some more recent reviews, IV drug users
and/or HIV positive patients appear to be at greater risk than the average population. Some
believe presence of abscess within the fascia is more suggestive of a hematogenous source.
 Secondary Psoas Abscess: Most (about 80%) are from a GI source. Crohn’s disease,
diverticulitis, appendicitis, or carcinoma are the main causes. A less common cause is spinal
osteomyelitis and discitis with one aberrant series citing these in 26% of cases. Tuberculosis
is still on the differential as well. Other causes include: perinephric abscess, leukemia, septic
arthritis, trauma, foreign body, and post-operative infection. These patients tend to be older
with incidence in males and females being about even. Secondary abscesses occur more
frequently on the right side (secondary to Crohn’s and appendicitis being more right colonic
issues). As one would expect given the etiolog of these organisms, the cultures tend to be
mixed with a preponderance of gram negatives from the gut. Staph and strep are still
frequently isolated in these mixed infections. Abscess external to the fascia is felt by some to
be suggestive of direct extension from adjacent organs.
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Clinical Presentation
Often difficult to diagnose based on history and physical alone. The classic presentation includes fever,
flank pain, abdominal pain, limp, and hip flexion contracture (flexion and external rotation of the ipsilateral
hip). Sometimes the pain of the abscess will radiate to the inguinal region and is occasionally associated
with a palpable inguinal mass. Pain may also radiate to the hip, thigh, or knee. Psoas abscess may also
be the cause of fevers of unknown origin, following a more chronic course with long-term fevers,
constitutional symptoms, and weight loss. Other findings include absent femoral pulse, rectal
tenderness, and wasting of the quadriceps femoris muscle. Labs are significant for leukocytosis and if
checked an elevated ESR. Anemia and pyuria may also be non-specific lab findings. Definitive
diagnosis is with an imaging modality. The most frequently used is the CT scan or ultrasound. The
benefit of the CT is that it can evaluate the patient for the etiology of the abscess if found. This may
change management. Calcification of the psoas is suggestive of a mycobacterial infection. 40-70% of
patients will have positive bacterial blood cultures.
Treatment/Prognosis
Like all abscesses, treatment is interdisciplinary with surgical and medical co-management. Empiric
antibiotics should include agents that cover bowel flora as well as S. aureus. In cases where bowel
pathology is identified, open surgery is the preferred route of draining these abscesses. In cases where
no bowel pathology is identified, the approach tends to be more percutaneous drainage with the help of
CT or US guidance. Antibiotics alone do not tend to be enough, especially in secondary abscess with a
50% failure rate reported by some sources. There has been some success with treatment of primary
abscess with antibiotics alone. Duration of therapy is usually 2-3 weeks after defervescence and
cessation of drainage. Mortality from primary abscess is 2.5% with secondary abscess carrying a nearly
20% mortality rate. Mortality increases with delay of definitive treatment.
Rare Complication: Meningitis
As noted above, the vascular supply of the psoas muscle is in communication with the paravertebral
venous plexus. The lack of valves in this system allows the direction of blood flow to be dependant on
intrathoracic and intraabdominal pressure. This is the suspected mechanism for seeding of the psoas by
extension of spinal osteomyelitis and discitis. Though rare, the reverse direction of infection may also
occur with psoas abscesses leading to epidural abscesses, osteomyelitis, and meningitis. In reviewing
the literature only a handful of cases of psoas muscle abscess leading to meningitis have been reported.
Of those cases, the majority have been caused by secondary psoas abscess from an intestinal source.
Only one other case of primary psoas abscess leading to S. aureus meningitis exists in the literature.
The take home message is to remember that the psoas is close to many organs and neurological
structures that share its blood flow. Care should be taken to treat these abscesses with appropriate
antibiotics and surgical management to avoid associated complications.
Bibliography
Desandre, AR. Iliopsoas Abscess: Etilogy, Diagnosis. And Treatment. Am Surg. 1995: 61: 1087-91.
Gruenwald, I. Psoas Abscess: Case Report and Review of the Literature. J. Uro. 1992: 147: 1624-6.
Orrison, WW. Fatal meningitis secondary to undetected bacterial psoas abscess. J. Neurosurg. 1977;
47:755-760.
Spotkov, Jared. Staphylococcal meningitis: a complication of psoas abscess. Neurology 1985; 35: 110111.
Van Dellen, JR. Meningitis caused by psoas abscess. South African Medical Journal. 1980; 52: 552-3.
Beth Israel Deaconess Medical Center Residents’ Report
Beth Israel Deaconess Medical Center Residents’ Report