Teaching Case

A 12-year-old female with fever, vomiting, rhinorrhoea, and frontal headache since three days ago. On examination, there is forehead swelling. A brain MRI is ordered.

A contrast-enhanced MRI examination is performed, showing sinusitis in frontal sinuses, ethmoid cells, and maxillary sinuses (Figures 1a, 1b, and 1c).

As a complication, it is observed a subperiosteal abscess associated with frontal bone, and osteomyelitis of the frontal bone known as Pott’s puffy tumour. It shows as a hypointense mass on T1 with important peripheral enhancement (Figures 2a and 2b) and significantly restricted diffusion with hyperintensity on diffusion-weighted images (DWI) correlating with clearly low apparent diffusion coefficient values (ADC), being compatible with abscess (Figures 2c and 2d).

It is associated with a central frontal empyema, shows as an extra-axial lesion with apparent capsule (Figures 3a and 3b) and restriction with corresponding signal loss on the ADC Map (Figures 3c and 3d). It conditions a compressive effect on the adjacent parenchyma and an area of cerebritis that shows as an area with diffusion restriction (Figures 4a and 4b).

A CT showed frontal sinusitis with extension through the frontal bone to the soft tissues and erosion of the bone, suggesting osteomyelitis (Figures 5a, 5b and 5c).

Pott’s puffy tumour (PPT) is a subperiosteal abscess with osteomyelitis of the frontal bone [1]. The frequency of this rare entity has increased recently [2].

PPT pathophysiology is explained by the extension of frontal sinusitis to the frontal bone through the diploic veins, causing osteomyelitis, and a consequent subperiosteal abscess. Although it has also been described after craniocerebral trauma [2,3]. PPT incidence is higher in children and adolescents, being rarer in adults [1]. It is because the frontal sinus is developing, which means increased flow through the diploic veins [3].

PTT is usually polymicrobial, with Staphylococci, Streptococci, Haemophilus influenzae, and anaerobic microorganisms being isolated, among others [2,3].

For its diagnosis, physical examination and an adequate clinical history are of great importance [4]. Symptoms may include forehead swelling, rhinorrhoea, fever, and intense pain with pressure on the frontal sinuses [2,4].

Imaging, particularly magnetic resonance imaging (MRI), is crucial in the characterisation of PTT and the detection of its complications. MRI reveals a mass with important peripheral enhancement and significantly restricted diffusion [5]. PTT may be associated with potentially dangerous intracranial extension with epidural or subdural abscess, meningitis, cerebritis, or brain abscess. Other complications include orbital cellulitis and cerebral venous thrombosis [3]. It is crucial to detect these possible associated complications early for proper management [3,5].

Management is habitually surgical with drainage of the abscess and with intravenous antibiotics. Imaging tests are essential for planning surgery [5,6]. The prognosis is generally favourable, especially with an early diagnosis and treatment to reduce morbidity and mortality [6].

Written informed patient consent for publication has been obtained.