CASE 17701 Published on 11.04.2022

Actinomyces cranial osteomyelitis with subdural empyema



Case Type

Clinical Cases


Natanael Vázquez

High Specialty Regional Hospital of el Bajio, Radiology Department, Leon, Guanajuato, Mexico


45 years, male

Area of Interest Neuroradiology brain ; Imaging Technique MR
Clinical History

A 45 year-old-patient with history of penetrating head trauma caused by a bull horn 1 year prior to evaluation, presented 3 episodes of epileptic seizures in the last 6 months. A non-enhanced head CT scan (not shown) reported an extra-axial frontal lesion suggesting meningioma; a brain MRI was ordered for further evaluation

The patient was taken to surgery 3 months later where the lesion was excised. Histopathological evaluation found granulomatous necrosis with microorganisms that had yellow sulfur granules (Figure 2).

Imaging Findings

MR evaluation showed an extra-axial left frontal lesion that invaded the adjacent cranium, as well as the brain parenchyma, and had extensive vasogenic oedema (Figure 1).

A second MRI was obtained after surgery, which showed a subdural liquid behaving collection with a well defined enhancing capsule in postgadoliniumsequences, located at the surgical site. (Figure 3).

Control MRI was obtained 6 months later showing complete resolution of the lesion (Figure 4).


Actinomyces are non-spore-forming, strict or facultative anaerobes with a variable cellular morphology. They are normal constituents of the oral flora and are also found in soil [1]. Human actinomycosis is primarily caused by Actinomyces israelii, but lately Actinomyces meyeri infections’ prevalence has increased [2]. Patients with poor oral hygiene and some immunosuppressive conditions are recognized as risk factors.

Actynomices can reach the brain by direct extension (dental procedure/abscess or trauma), but hematogenous spread has been described. Most central nervous infections manifest as brain abscesses, but meningitis, encephalitis, subdural empyema and epidural abscess can happen as well [1]. In our case the presence of penetrating head trauma and exposure to contaminated soil seemed to be the cause of the cranial infection, since the patient received a full dental work up and no evidence of dental infection was found.

Clinical manifestations include insidious headache, seizures and focal neurological deficit. Fever may or may not be present [3].

On MR imaging, actinomycotic abscesses are seen as an irregular, nodular lesion with peripheral enhancement; the core’s signal intensity is variable depending on the phase. It can extend to the adjacent bone causing osteomyelitis. Restricted diffusion of the core is often seen [4]. It can also mimic a malignant tumour on occasions [5]. Histopathological evaluation with identification of the pathogen as well as yellow “sulfur” granules is key for diagnosis.

Conventional therapy for actinomyces infections involves long course treatments of beta-lactam antibiotics. Surgical debridement is also recommended [4]. Prognosis is good when treatment is established early.


Actinomyces infections can reach the central nervous system not only from dental sources. Trauma with direct inoculation can happen and extension through continuity can affect the bone, the meninges and even the brain. It is important to consider this when evaluation an intracranial lesion since establishing the appropriate therapy early in the course of the disease, can change dramatically the patient’s prognosis. 

Written informed patient consent for publication has been obtained.

Differential Diagnosis List
Actinomyces osteomyelitis with subdural empyema
High grade meningioma
Pachymeningeal metastases
High grade oligodendroglioma
Final Diagnosis
Actinomyces osteomyelitis with subdural empyema
Case information
DOI: 10.35100/eurorad/case.17701
ISSN: 1563-4086