An 83-year-old female patient was admitted to the emergency department of our hospital one hour after onset of right-sided hemiparesis and right-sided hemianopia. There was no relevant medical history.
Computed tomography (CT) of the brain revealed no intracranial haemorrhage nor imaging signs of acute ischaemia (Fig. 1). Incidentally, an enlarged left frontal sinus with unilateral osseous expansion of the adjacent frontal bone and the greater wing of the sphenoid was seen. Moreover, the affected bones were sclerotic with areas of interspersed radiolucency (Fig. 1,2).
Subsequent magnetic resonance imaging (MRI) was performed the next day to confirm the clinical suspicion of ischaemic stroke and to exclude haemorrhagic transformation after tissue Plasminogen Activator (tPA) administration. MRI revealed a subtle focus of acute ischaemia in the left lentiform nucleus, visualised as a hyperintense signal on FLAIR with diffusion restriction on diffusion weighted imaging (DWI). The osseous lesion in the left frontal bone demonstrated intermediate signal intensity on T1-weighted imaging and predominantly high signal on T2-weighted imaging. Gadolinium enhancement was inhomogeneous but without any extra-axial nor intra-axial enhancement of the brain (Fig. 3).
Pneumosinus dilatans (PSD) refers to an air-filled paranasal sinus, abnormally enlarged beyond the normal boundaries of the skull bones, and in the absence of osseous erosion, hyperostosis, or mucous membrane thickening [1]. Although the condition was first described by Meyes in 1898, the term ‘pneumosinus dilatans’ was coined by Benjamins in 1918 [2].
PSD is a rare condition with an unknown true incidence [3]. It occurs most frequently in the frontal sinuses, followed by the sphenoid, ethmoid, and maxillary sinuses [4].
The imaging characteristics for PSD are straightforward on both CT and MRI, i.e. expansion of a paranasal sinus with normal wall thickness [3]. PSD is often an incidental finding [3,5]. Unilateral frontal bossing may be present as a clinical sign [6].
The key role of imaging is to evaluate the presence of underlying conditions [3]. There is a documented association between PSD and fibrous dysplasia [7], meningiomas [3], arachnoid cysts [8], port-wine stains [9], hydrocephalus [10], but it can also be idiopathic [5]. PSD may cause spontaneous pneumocephalus [11].
The pathophysiology of PSD remains unclear, although many hypotheses have been postulated. The most cited theory comprises a one-way valve, creating a pressure gradient, thus increasing the outward pressure on the sinus wall [3,12,13]. A traction phenomenon due to an adjacent meningioma with subsequent bone remodelling has been suggested as well [3]. Whether these theories can be extrapolated to other causes of PSD such as fibrous dysplasia is still debated.
Fibrous dysplasia (FD) is a non-hereditary, benign bone disease. It is characterised by abnormal osteoblastic differentiation and maturation, leading to focal replacement of normal bone tissue by fibrous stroma and islands of immature bone [14]. FD manifests as an expansile bone lesion with smooth cortical contours. Its most common appearance on CT is that of ground-glass density, but it may be homogeneously sclerotic and even cystic [14,15]. MRI appearance is highly variable due to the variation in cellularity of FD. T1-weighted imaging may yield low to intermediate signal intensities, T2-weighted imaging may demonstrate low to high signal intensities. Similarly, gadolinium enhancement is highly variable [15].
Treatment of PSD is directed at surgically correcting the cosmetic deformity of the skull bone, and endoscopic restoration of sinus drainage [5].
In conclusion, the importance of pneumosinus dilatans is to recognise this type of sinus expansion as a clue to potential underlying pathologies.
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Pneumosinus frontalis dilatans with associated craniofacial fibrous dysplasia
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1. CT scan and bone window images show: The left frontal sinus is significantly dilated, with clear boundaries and no apparent wall destruction or thickening, corresponding to “sinus expansion” or “pneumosinus dilatans.”
2. In the left frontal bone adjacent to the frontal sinus, there is an increased bone density area with partial “ground-glass” appearance and relatively dense shadow. The bone trabecular structure is disordered, but the shape and boundary remain relatively regular, suggestive of fibrous bone disease (fibrous proliferation or fibrous structure).
3. MRI sequences (T1, T2, FLAIR, and T1 with contrast) show that the lesion in the left frontal bone presents as T1 isointense or slightly hypointense signal and heterogeneous T2 signal. Mild heterogeneous enhancement is observed, consistent with the diverse MRI appearances of fibrous dysplasia.
4. No definite intracranial soft tissue mass or obvious enhancing lesion is seen, and no obvious intracerebral hemorrhage is detected. If this is an emergency scan, acute stroke sequences should be reviewed to exclude the possibility of acute ischemic lesions (in this case, there is a suspicious slight signal change in the left cerebral region possibly related to right-sided limb paralysis, requiring further exclusion or confirmation of stroke).
Based on the above imaging findings and the patient’s clinical status, possible diagnoses or differential diagnoses include:
1. Pneumosinus Dilatans of the frontal sinus with Fibrous Dysplasia:
- Marked expansion of the frontal sinus but with intact boundaries suggests excessive aeration or bulging of the sinus wall;
- Concurrent “ground-glass” changes in the frontal bone are consistent with the CT and MRI findings common in fibrous dysplasia;
- Fibrous dysplasia can cause local bone structural changes and expansive growth, so when it coincides with sinus expansion, this combination should be highly suspected.
2. Sinus expansion associated with other lesions (e.g., meningioma or other intracranial lesions):
- Although no typical meningioma signal or intracranial soft tissue mass is noted in this case, it remains in the differential;
- Intracranial tumors, such as meningioma, may cause focal bone remodeling or wall changes through traction or compression.
3. Other rare craniofacial abnormalities or congenital variations:
- For instance, rare craniofacial developmental abnormalities or localized cystic changes, which do not fully match this case’s presentation.
Considering the patient’s clinical symptoms (acute right-sided hemiplegia and right-sided hemianopia suggesting acute stroke component), advanced age, and imaging features (significant left frontal sinus dilatation, “ground-glass” density changes in the frontal bone), the most likely diagnosis is:
“Left frontal sinus Pneumosinus Dilatans with associated Fibrous Dysplasia.”
If further exclusion of meningioma or confirmation of stroke type is needed, enhanced MRI or multi-sequence stroke screening can be performed. If there is any doubt about the nature of fibrous dysplasia, a biopsy can be considered to confirm the pathological diagnosis.
1. Basic Treatment Strategy:
- In cases discovered incidentally without significant increased intracranial pressure or severe cosmetic concerns, periodic imaging follow-up can be conducted to monitor disease progression;
- If there is noticeable bony protrusion affecting appearance, or severe symptoms (e.g., recurrent headaches, involvement of vital structures), surgical intervention can be considered, including craniofacial reconstruction or endoscopic restoration of sinus ventilation as appropriate;
- Monitor and manage potential complications associated with fibrous dysplasia, such as evaluating the feasibility of surgical removal or resection of diseased bone if symptomatic.
2. Rehabilitation and Exercise Guidance (FITT-VP Principle)
For this patient who may have right-sided weakness post-stroke, an individualized and gradual rehabilitation plan is particularly important.
- Frequency: Rehabilitation training 3–5 times a week, initially based on fatigue level and bone condition, potentially increasing to multiple short low-intensity sessions daily;
- Intensity: Begin with low intensity (e.g., passive range-of-motion exercise, joint mobility training), then gradually progress to mild-to-moderate resistance training or functional activities;
- Time: Each session lasting 15–30 minutes, with sufficient rest periods. Duration may be extended as tolerated;
- Type: Early-stage exercises focus on simple joint mobility and muscle strength training, followed by gait training with assistive devices and simple activities of daily living once some strength returns;
- Progression: Increase exercise intensity steadily based on improvements in balance, cardiopulmonary endurance, and bone condition. After achieving basic daily living activities, add more complex exercises (e.g., stair climbing);
- Volume and Individualization: Overall exercise volume should be estimated in consideration of patient’s age, skeletal safety, and cardiovascular condition, adjusting to avoid excessive strain or increased fracture risk.
3. Other Considerations:
- Monitor blood pressure and cardiac function. If necessary, perform ECG or simple cardiopulmonary assessments prior to rehabilitation;
- Due to abnormal bone structure, avoid significant impact or falls that could induce fractures or cranial injuries;
- Schedule regular imaging follow-up to assess the progression of sinus expansion and fibrous dysplasia and to detect any potential new complications at an early stage.
Disclaimer:
The above report is a reference analysis based on imaging and publicly available data. It does not replace in-person consultation or a certified physician’s diagnosis. Specific treatment plans should be determined by a licensed physician based on the patient’s comprehensive condition.
Pneumosinus frontalis dilatans with associated craniofacial fibrous dysplasia
