The causative organism turned out to be methicillin-susceptible Staphylococcus aureus, or MSSA, the antibiotic-sensitive cousin of the notorious drug-resistant MRSA. That susceptibility detail matters enormously, because it opened the door to targeted antimicrobial therapy once cultures confirmed the pathogen. The diagnosis began with the iliopsoas abscess, a walled-off pocket of pus within the muscle group that flexes the hip and stabilizes the lumbar spine. Computed tomography guided the placement of a drainage catheter into that collection, and culture of the drained material yielded MSSA. But the spinal collection was the more alarming finding. Magnetic resonance imaging revealed a spinal subdural abscess, an accumulation of pus within the dura mater but outside the arachnoid membrane, extending across twelve vertebral segments and compressing the neurological structures responsible for movement and sensation in the lower limbs.

Spinal subdural abscesses are exceedingly rare. Most clinicians are far more familiar with spinal epidural abscesses, which form in the fat-filled space outside the dura and are far more common. A subdural collection is anatomically confined, lying beneath the toughest membrane covering the spinal cord, and its rarity in the literature means there are no large trials to guide treatment. The situation becomes even more complicated in elderly patients, who tolerate both the infection and the surgery poorly, and in critically ill patients whose organ systems are already failing. The combination of a spinal subdural abscess with a concurrent iliopsoas abscess, both attributable to the same organism in a septic 75-year-old, has been reported so infrequently that the authors of the new report describe the association as poorly understood.

The diagnostic puzzle in this case illustrates a common frustration in infectious disease management. Because the patient had already received antibiotics before surgeons could obtain specimens from the spine, the intraoperative cultures from the subdural collection came back negative. Prior antimicrobial exposure can sterilize cultures without fully eradicating infection, leaving clinicians to infer the pathogen indirectly. The team therefore attributed the spinal abscess presumptively to MSSA, based on the organism recovered from the iliopsoas collection and the overall clinical picture. Importantly, the authors are careful about what this inference can and cannot establish. They note that hematogenous seeding, in which bacteria traveling through the bloodstream plant themselves directly in the spine, could not be excluded as an alternative mechanism.

Nevertheless, the clinical history and radiological findings led the team to propose a hypothesis that is anatomically provocative: that the infection may have spread contiguously, traveling from the iliopsoas abscess upward into the spinal subdural space along adjacent tissue planes. The iliopsoas muscle sits in direct anatomical proximity to the lumbar spine, and collections in this compartment are known in other contexts to track along fascial planes and communicate with the vertebral column. If contiguous spread were confirmed in future studies, it would give clinicians a concrete warning sign: an iliopsoas abscess in a patient with back pain and neurological symptoms should raise immediate suspicion of intraspinal extension, prompting urgent magnetic resonance imaging rather than watchful waiting. The authors explicitly frame this pathway as one of several plausible hypotheses rather than an established route, a distinction that reflects the epistemic honesty required when a single case cannot settle a mechanistic question.

Treatment required a coordinated, three-pronged assault. First came source control: the CT-guided drainage of the iliopsoas collection, which both relieved the local infection and provided the diagnostic material. Second was targeted antimicrobial therapy, selected once the susceptibility profile of the isolated strain was known. The supplementary data accompanying the report include a detailed antimicrobial susceptibility table covering sixteen antibiotics and two screening tests, reflecting the standard laboratory workup that transforms a presumptive diagnosis into a precise prescription. Third, and most technically demanding, was surgery on the spine itself. The team performed a decompressive laminectomy at the L1 to L3 levels, removing the bony arches of three vertebrae to access the abscess, while deliberately sparing the arachnoid membrane.

That arachnoid-sparing technique deserves particular attention, because it represents the surgical tightrope in subdural abscess management. The surgeon must drain the purulent material beneath the dura while avoiding violation of the arachnoid layer, which separates the abscess from the cerebrospinal fluid that bathes the spinal cord. Breaching that membrane risks disseminating infection into the cerebrospinal fluid, converting a localized subdural collection into meningitis, one of the most feared complications in neurosurgery. It also risks cerebrospinal fluid leakage and its cascade of secondary problems. The success of the procedure in this case, achieved across an abscess spanning from the thoracolumbar junction to the sacrum, demonstrates that decompressive drainage can be accomplished without contaminating the cerebrospinal spaces.

The outcome was a full recovery on both fronts that matter most in sepsis. The infection was controlled, with the patient’s organ function recovering from the septic insult, and his neurological function returned as the compression on his spinal cord was relieved. Follow-up over six months documented no clinical recurrence, a meaningful benchmark given that abscesses can reaccumulate if any residual collection or devitalized tissue is left behind. In an infection category with a mortality rate exceeding 30 percent when the central nervous system is involved, a survival with preserved neurological function and durable remission is a genuinely favorable result, and the case report attributes it directly to the speed of diagnosis, the precision of the pathogen-targeted antimicrobial regimen, and the arachnoid-sparing surgical drainage.

Beyond its clinical particulars, the case carries lessons about how medicine handles the diseases it rarely encounters. Evidence hierarchies prize randomized trials, but no trial will ever enroll enough spinal subdural abscesses to guide practice, because the condition is too uncommon. In that vacuum, carefully documented case reports become the working literature of the field, accumulating one patient at a time into something like a collective textbook. The value of such reports depends entirely on the discipline of the documentation: the explicit acknowledgment that a proposed spread pathway is a hypothesis, the transparency about culture-negative results and their likely cause, and the publication of the full clinical timeline and susceptibility data in supplementary materials. The authors state that no artificial intelligence tools were used in preparing the manuscript, and the work was supported by research grants from the Sichuan Medical Association, the Panzhihua Science and Technology Bureau, and the Sichuan Association for Medical Science and Technology Innovation.

For frontline clinicians, the practical message is one of heightened vigilance. An elderly patient presenting with fever, back pain, and evolving leg weakness is not a candidate for observation; that triad demands urgent imaging and blood cultures, and an iliopsoas abscess discovered on imaging should trigger scrutiny of the spine. The bacterium at the center of this case remains one of the most common and adaptable human pathogens, capable of colonizing skin and nasal passages silently before invading deep tissue compartments. When it does, the difference between recovery and death often comes down to hours: the hours before drainage, before effective antibiotics, and before the expanding abscess inflicts irreversible damage on the nervous system it has invaded. This Chinese case report adds one more documented battle to that ongoing clinical war, and one more hypothesis for researchers to test as they map the hidden routes by which Staphylococcus aureus travels from muscle to meninges.

Subject of Research: A rare case of spinal subdural abscess with concurrent iliopsoas abscess caused by methicillin-susceptible Staphylococcus aureus in an elderly critically ill patient

Article Title: Severe multisite methicillin-susceptible Staphylococcus aureus infection in an elderly critically ill patient: a case report of spinal subdural abscess with concomitant iliopsoas abscess

Article References: Severe multisite methicillin-susceptible Staphylococcus aureus infection in an elderly critically ill patient: a case report of spinal subdural abscess with concomitant iliopsoas abscess. (n.d.). https://doi.org/10.1186/s12879-026-14636-1

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14636-1

Keywords: Staphylococcus aureus, MSSA, spinal subdural abscess, iliopsoas abscess, sepsis, case report, laminectomy, antimicrobial therapy, central nervous system infection, contiguous spread, elderly patients, BMC Infectious Diseases