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Department of Radiology
Seth G.S. Medical College and K.E.M. Hospital, Mumbai , India
Case of the Month
Case of the Month
A Hard Case to Crack : Solitary Fibrous Tumour of the Skull
A Hard Case to Crack : Solitary Fibrous Tumour of the Skull
Contributed by : Rushikesh Janwale
Contributed by : Rushikesh Janwale
Introduction :
Introduction :
Slowly enlarging masses over the scalp or skull present a diagnostic challenge and often raise concern about underlying bone and intracranial involvement. Such lesions may originate from the calvarium, meninges, or soft tissues, and the clinical presentation can vary widely depending on the lesion’s location, growth pattern, and involvement of adjacent structures. When a patient presents with a long-standing, progressively increasing swelling in the cranial region, particularly in the parieto-occipital area, a broad differential diagnosis must be considered—ranging from benign entities such as epidermoid cysts, lipomas, or intraosseous haemangiomas to more aggressive lesions like meningiomas, metastases, or solitary fibrous tumours (previously termed hemangiopericytomas).
Slowly enlarging masses over the scalp or skull present a diagnostic challenge and often raise concern about underlying bone and intracranial involvement. Such lesions may originate from the calvarium, meninges, or soft tissues, and the clinical presentation can vary widely depending on the lesion’s location, growth pattern, and involvement of adjacent structures. When a patient presents with a long-standing, progressively increasing swelling in the cranial region, particularly in the parieto-occipital area, a broad differential diagnosis must be considered—ranging from benign entities such as epidermoid cysts, lipomas, or intraosseous haemangiomas to more aggressive lesions like meningiomas, metastases, or solitary fibrous tumours (previously termed hemangiopericytomas).
These masses can remain asymptomatic for years or cause pressure effects such as headaches, neurological deficits, or cosmetic disfigurement. Radiologic evaluation is essential to characterize the lesion size, origin, vascularity, bone involvement and possible intracranial extension. Imaging modalities like CT and MRI are particularly helpful in assessing the lesion’s enhancement pattern, dural involvement, and mass effect. A lobulated, enhancing, and erosive lesion with both intra- and extracranial components in a middle-aged adult warrants careful evaluation to distinguish between primary skull tumours and metastatic disease, as management strategies and prognosis differ significantly based on the final diagnosis.
These masses can remain asymptomatic for years or cause pressure effects such as headaches, neurological deficits, or cosmetic disfigurement. Radiologic evaluation is essential to characterize the lesion size, origin, vascularity, bone involvement and possible intracranial extension. Imaging modalities like CT and MRI are particularly helpful in assessing the lesion’s enhancement pattern, dural involvement, and mass effect. A lobulated, enhancing, and erosive lesion with both intra- and extracranial components in a middle-aged adult warrants careful evaluation to distinguish between primary skull tumours and metastatic disease, as management strategies and prognosis differ significantly based on the final diagnosis.
We present a case of a solitary fibrous tumor originating from the skull in an adult patient, which radiologically resembled a hemangiopericytoma across all imaging modalities. This report highlights the diagnostic challenges, imaging features, and the importance of histopathological correlation in arriving at the correct diagnosis.
We present a case of a solitary fibrous tumor originating from the skull in an adult patient, which radiologically resembled a hemangiopericytoma across all imaging modalities. This report highlights the diagnostic challenges, imaging features, and the importance of histopathological correlation in arriving at the correct diagnosis.
Clinical Profile:
Clinical Profile:
A 49 year old man came with altered sensorium since one week and a swelling over the left parieto-occipital region since four years (Fig. 1). The swelling had gradually increased in size. The overlying skin was normal.
A 49 year old man came with altered sensorium since one week and a swelling over the left parieto-occipital region since four years (Fig. 1). The swelling had gradually increased in size. The overlying skin was normal.
Fig 1
A large, lobulated swelling is noted over the left parieto-occipital region with no overlying skin changes. The scalp vessels are prominent.
Radiological findings :
Radiological findings :
Frontal and lateral skull radiographs (Fig. 2) show a well-circumscribed lytic lesion in the left high parietal region involving both, the inner and outer tables of the skull. It measures approximately 3x5cm with surrounding soft tissue. There is a narrow zone of transition. The lesion shows no sclerotic margins, calcifications or any periosteal reaction.
Frontal and lateral skull radiographs (Fig. 2) show a well-circumscribed lytic lesion in the left high parietal region involving both, the inner and outer tables of the skull. It measures approximately 3x5cm with surrounding soft tissue. There is a narrow zone of transition. The lesion shows no sclerotic margins, calcifications or any periosteal reaction.
Fig 2
Frontal and lateral radiographs of the skull show a well-circumscribed lytic lesion in the left high parietal region measuring 3 x 5 cm. It involves the inner and outer tables of the skull with a narrow zone of transition.
Contrast enhanced CT scan (Fig. 3) of the brain shows a lobulated, extra-axial, vividly enhancing heterogeneous lesion in the left parieto-occipital region. There is complete erosion of the inner and outer tables of the skull along with extracranial extension. There is an intraaxial component involving the left occipital lobe causing complete effacement of the occipital horn of the left lateral ventricle. There is midline shift to the right.
Contrast enhanced CT scan (Fig. 3) of the brain shows a lobulated, extra-axial, vividly enhancing heterogeneous lesion in the left parieto-occipital region. There is complete erosion of the inner and outer tables of the skull along with extracranial extension. There is an intraaxial component involving the left occipital lobe causing complete effacement of the occipital horn of the left lateral ventricle. There is midline shift to the right.
Figure 3 A- Plain CT scan of the brain shows a iso to hyperdense, extra-axial, lobulated, lesion in the left parieto-occipital region.
Figure 3 B, C, D- There is erosion of the inner and outer tables of the left parietal bone.
Figure 3 E, F, G- On post contrast images the lesion is vividly enhancing and heterogeneous. An intraaxial component is noted in the left occipital lobe. Mass effect is noted in the form of a midline shift to the right.
MRI of the brain (Fig. 4) shows a large well-defined, extra-axial, exophytic, lobulated, heterogeneously T2/FLAIR iso to hyperintense and T1 iso-intense lesion in the left parietal region causing erosion and destruction of the parietal bone. It measures approximately 9 x 8 x 9.5 cm. There are chunky areas of susceptibility in the lesion on SWI indicating calcifications. There are patchy areas of diffusion restriction in the lesion. There is heterogeneous post contrast enhancement with few non-enhancing cystic areas. There is an area of dural breach with intracranial extension of the lesion. Multiple prominent flow voids are noted in the periphery of the lesion and the overlying scalp of the parietal and temporal regions.
MRI of the brain (Fig. 4) shows a large well-defined, extra-axial, exophytic, lobulated, heterogeneously T2/FLAIR iso to hyperintense and T1 iso-intense lesion in the left parietal region causing erosion and destruction of the parietal bone. It measures approximately 9 x 8 x 9.5 cm. There are chunky areas of susceptibility in the lesion on SWI indicating calcifications. There are patchy areas of diffusion restriction in the lesion. There is heterogeneous post contrast enhancement with few non-enhancing cystic areas. There is an area of dural breach with intracranial extension of the lesion. Multiple prominent flow voids are noted in the periphery of the lesion and the overlying scalp of the parietal and temporal regions.
Figure 4 A, B, C- MRI brain shows a large well-defined, extra-axial, exophytic, lobulated, heterogeneously T2/FLAIR iso to hypointense and T1 iso-intense lesion in left parietal region causing erosion and destruction of the parietal bone.
Figure 4 D, E, F, G- Heterogeneous post-contrast enhancement is n. There are chunky areas of susceptibility in the lesion on SWI suggestive of calcifications. There are patchy areas of diffusion restriction in the lesion.
Radiological diagnosis:
Radiological diagnosis:
The differential diagnosis include hemangiopericytoma, metastasis, atypical meningioma.
The differential diagnosis include hemangiopericytoma, metastasis, atypical meningioma.
Management:
Management:
Surgical resection of the tumor was performed (Fig. 5). Post-operatively the patient’s sensorium improved. Few days after being discharged, the patient was brought back with headache, fever and signs of meningeal irritation. There was improvement following a course of intravenous antibiotics.
Surgical resection of the tumor was performed (Fig. 5). Post-operatively the patient’s sensorium improved. Few days after being discharged, the patient was brought back with headache, fever and signs of meningeal irritation. There was improvement following a course of intravenous antibiotics.
Fig. 5 : The resected specimen
Pathological diagnosis:
Pathological diagnosis:
Solitary fibrous tumour (WHO grade 2). FIg. 6
Solitary fibrous tumour (WHO grade 2). FIg. 6
Fig 6: A highly cellular tumor is seen composed of spindle cells arranged in fascicles. Focally storiform pattern is seen, and at places, they are in sheets. The cells have oval nuclei with mild nuclear pleomorphism. There are foci of necrosis and adipocytic differentiation. The tumor cells are interspersed with numerous vessels, many of them being dilated and 'staghorn' type. The tumor infiltrates the adjacent bone. The mitotic count is 6-8/high power field
Timeline
Timeline
Discussion:
Discussion:
In our patient, while the radiological features suggest an aggressive lesion, the clinical course and behavior of the mass over several years provide ia a crucial context for diagnosis.
In our patient, while the radiological features suggest an aggressive lesion, the clinical course and behavior of the mass over several years provide ia a crucial context for diagnosis.
In this age group, differential diagnoses for an expansile skull lesion with soft tissue component and dural breach include metastasis, atypical meningioma, and hemangiopericytoma/solitary fibrous tumor (HPC/SFT). Of these, metastasis is an important consideration, particularly given its prevalence in adults over 40. However, metastases tend to present with more rapid onset, are often multifocal, and usually occur in the context of a known systemic malignancy. In contrast, this patient had a solitary, slowly growing lesion with no known primary malignancy, making metastasis less likely.
In this age group, differential diagnoses for an expansile skull lesion with soft tissue component and dural breach include metastasis, atypical meningioma, and hemangiopericytoma/solitary fibrous tumor (HPC/SFT). Of these, metastasis is an important consideration, particularly given its prevalence in adults over 40. However, metastases tend to present with more rapid onset, are often multifocal, and usually occur in the context of a known systemic malignancy. In contrast, this patient had a solitary, slowly growing lesion with no known primary malignancy, making metastasis less likely.
Hemangiopericytomas are rare, aggressive mesenchymal tumors that arise from pericytes and have been reclassified under the spectrum of solitary fibrous tumors as cellular variants of SFT [1]. They account for less than 1% of all intracranial tumors and commonly affect middle-aged adults [2]. These tumors are characteristically extra-axial, highly vascular, and vividly enhancing, often causing erosion of the adjacent bone without calcification or hyperostosis—features that help distinguish them from meningiomas [3,4,5]. Hemangiopericytomas tend to recur locally and may metastasize in late stages—commonly to the lungs, liver, or bones [6,7]. MRI may show flow voids due to their vascularity, and SWI sequences may reveal susceptibility from hemorrhage [2,3]. Histologically, they express STAT6 due to NAB2–STAT6 fusion, which helps confirm the diagnosis [1].
Hemangiopericytomas are rare, aggressive mesenchymal tumors that arise from pericytes and have been reclassified under the spectrum of solitary fibrous tumors as cellular variants of SFT [1]. They account for less than 1% of all intracranial tumors and commonly affect middle-aged adults [2]. These tumors are characteristically extra-axial, highly vascular, and vividly enhancing, often causing erosion of the adjacent bone without calcification or hyperostosis—features that help distinguish them from meningiomas [3,4,5]. Hemangiopericytomas tend to recur locally and may metastasize in late stages—commonly to the lungs, liver, or bones [6,7]. MRI may show flow voids due to their vascularity, and SWI sequences may reveal susceptibility from hemorrhage [2,3]. Histologically, they express STAT6 due to NAB2–STAT6 fusion, which helps confirm the diagnosis [1].
Solitary fibrous tumors are fibroblastic mesenchymal neoplasms that, though initially described in the pleura, are now known to occur at various extrapleural sites, including the meninges and skull [1]. These tumors exhibit a wide spectrum of biological behavior—from benign to malignant—making histopathological assessment crucial. On imaging, SFTs often appear as well-circumscribed, lobulated, extra-axial masses with intense enhancement, occasionally mimicking meningiomas or other hypervascular tumors [1,4]. While slow-growing, SFTs can demonstrate aggressive features such as bone erosion and intracranial extension, especially in larger lesions [1]. Immunohistochemistry plays a key diagnostic role, with diffuse nuclear STAT6 expression serving as a sensitive and specific marker due to the characteristic NAB2–STAT6 gene fusion [1,6]. According to the 2021 WHO classification of central nervous system tumors, solitary fibrous tumors and hemangiopericytomas are now considered a single entity, categorized under mesenchymal, non-meningothelial tumors, and graded as CNS WHO grade 1, 2, or 3 depending on histological features [8]. Complete surgical resection is the treatment of choice, but long-term follow-up is essential due to the potential for delayed recurrence and metastasis, even in histologically benign-appearing tumors [9,10].
Solitary fibrous tumors are fibroblastic mesenchymal neoplasms that, though initially described in the pleura, are now known to occur at various extrapleural sites, including the meninges and skull [1]. These tumors exhibit a wide spectrum of biological behavior—from benign to malignant—making histopathological assessment crucial. On imaging, SFTs often appear as well-circumscribed, lobulated, extra-axial masses with intense enhancement, occasionally mimicking meningiomas or other hypervascular tumors [1,4]. While slow-growing, SFTs can demonstrate aggressive features such as bone erosion and intracranial extension, especially in larger lesions [1]. Immunohistochemistry plays a key diagnostic role, with diffuse nuclear STAT6 expression serving as a sensitive and specific marker due to the characteristic NAB2–STAT6 gene fusion [1,6]. According to the 2021 WHO classification of central nervous system tumors, solitary fibrous tumors and hemangiopericytomas are now considered a single entity, categorized under mesenchymal, non-meningothelial tumors, and graded as CNS WHO grade 1, 2, or 3 depending on histological features [8]. Complete surgical resection is the treatment of choice, but long-term follow-up is essential due to the potential for delayed recurrence and metastasis, even in histologically benign-appearing tumors [9,10].
In this case, the long-standing clinical history, solitary and expansile nature of the lesion, bone erosion without hyperostosis, and lobulated vividly enhancing extra-axial mass favor the diagnosis of solitary fibrous tumor over metastasis or meningioma. Given the lesion's aggressive features, including intra-axial extension and mass effect, surgical resection followed by histopathological confirmation is essential. Due to the tumor's known risk for recurrence and distant spread, long-term follow-up with imaging and clinical surveillance is also crucial in management [8,9].
In this case, the long-standing clinical history, solitary and expansile nature of the lesion, bone erosion without hyperostosis, and lobulated vividly enhancing extra-axial mass favor the diagnosis of solitary fibrous tumor over metastasis or meningioma. Given the lesion's aggressive features, including intra-axial extension and mass effect, surgical resection followed by histopathological confirmation is essential. Due to the tumor's known risk for recurrence and distant spread, long-term follow-up with imaging and clinical surveillance is also crucial in management [8,9].
Conclusion :
Conclusion :
Solitary fibrous tumors of the skull are rare, diagnostically challenging lesions that can mimic other extra-axial neoplasms such as meningiomas or metastases, both clinically and radiologically. This case highlights the importance of integrating imaging features with clinical history and histopathological correlation for accurate diagnosis. The reclassification of hemangiopericytoma as part of the solitary fibrous tumor spectrum underscores the evolving understanding of these tumors and reinforces the need for immunohistochemical confirmation, particularly STAT6 nuclear expression. Surgical resection remains the cornerstone of treatment, and given the potential for late recurrence or metastasis, vigilant long-term follow-up is crucial. Awareness of this entity is essential for radiologists and treating physicians when evaluating slow-growing, enhancing skull lesions with aggressive imaging features.
Solitary fibrous tumors of the skull are rare, diagnostically challenging lesions that can mimic other extra-axial neoplasms such as meningiomas or metastases, both clinically and radiologically. This case highlights the importance of integrating imaging features with clinical history and histopathological correlation for accurate diagnosis. The reclassification of hemangiopericytoma as part of the solitary fibrous tumor spectrum underscores the evolving understanding of these tumors and reinforces the need for immunohistochemical confirmation, particularly STAT6 nuclear expression. Surgical resection remains the cornerstone of treatment, and given the potential for late recurrence or metastasis, vigilant long-term follow-up is crucial. Awareness of this entity is essential for radiologists and treating physicians when evaluating slow-growing, enhancing skull lesions with aggressive imaging features.
References:
References:
1. 1.Li X, et al. Magnetic resonance features of meningeal solitary fibrous tumors. Oncol Lett 2018;15(6):8825–32. doi:10.3892/ol.2018.8426.
1. 1.Li X, et al. Magnetic resonance features of meningeal solitary fibrous tumors. Oncol Lett 2018;15(6):8825–32. doi:10.3892/ol.2018.8426.
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2.Liu G, et al. Intracranial hemangiopericytoma: MR imaging findings and diagnostic usefulness of minimum ADC values. J Magn Reson Imaging 2013;38(5):1146–51. doi:10.1002/jmri.24075.
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Acknowledgements:
Acknowledgements:
We are grateful to the Departments of Neurosurgery and Pathology at our institutions for providing the photograms of the specimen and the histopathology images.
We are grateful to the Departments of Neurosurgery and Pathology at our institutions for providing the photograms of the specimen and the histopathology images.
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