Overview and definition
Psammomatoid ossifying fibroma (PsOF) is a benign fibro-osseous neoplasm characterized by replacement of normal bone with cellular fibrous stroma containing distinctive spherical calcified ossicles resembling psammoma bodies.[1][2] It predominantly affects the extragnathic craniofacial bones—particularly the frontal, ethmoid, and orbital bones—and less frequently involves the jaws.[3][4] The lesion is classified as a subtype of ossifying fibroma in the WHO classification of head and neck tumors, distinct from both cemento-ossifying fibroma and juvenile trabecular ossifying fibroma on clinical, morphologic, and molecular grounds.[5][6] PsOF is now recognized to harbor recurrent SATB2 gene rearrangements, supporting its status as a genetically distinct entity.[4] Although benign, PsOF demonstrates a propensity for locally aggressive behavior, including invasion of adjacent sinuses, orbit, and anterior cranial fossa, and carries a notable recurrence risk after conservative surgery.[2][7] Management centers on complete surgical excision.
Terminology and classification
Current classification
The 5th edition WHO classification of head and neck tumors lists PsOF among the fibro-osseous lesions within the section on odontogenic and maxillofacial bone tumors, separate from the general bone tumor classification.[6][8] It is recognized as a distinct subtype of ossifying fibroma alongside cemento-ossifying fibroma (COF) and juvenile trabecular ossifying fibroma (JTOF).[5]
Accepted names and aliases
- Psammomatoid ossifying fibroma (PsOF) — current preferred term[4][5]
- Juvenile psammomatoid ossifying fibroma (JPOF/PsJOF) — widely used synonym reflecting the younger age predilection[1][3]
Obsolete or potentially confusing terms
- "Aggressive psammomatoid ossifying fibroma" — used in older literature to emphasize locally destructive behavior but not a formal classification term[2]
- "Juvenile active ossifying fibroma" — an older umbrella term for both psammomatoid and trabecular variants[9]
- The qualifier "juvenile" is retained in much of the literature, though PsOF occurs across a wide age range and is not restricted to children[3][4]
Epidemiology
- Age: Broad range reported (3 months to 72 years), with a mean around 20 years; most cases present in adolescents and young adults, though PsOF affects a wider age range than JTOF.[3][7]
- Sex: A slight male predilection has been reported but remains disputed.[3]
- Frequency: Rare; PsOF is the more common of the two juvenile ossifying fibroma variants.[3]
- Anatomic distribution: The paranasal sinuses (especially ethmoid and maxillary), orbital bones, and fronto-ethmoidal complex are the characteristic sites. Jaw involvement (mandible more than maxilla) is less frequent but well documented. Skull base involvement is reported, with the majority of cases in one surgical series located in the skull base area.[1][2][7][10][11]
Clinical presentation
Presentation and symptoms
Most patients present with a slowly enlarging, painless swelling.[7][10] Symptoms depend on the anatomic site and size of the lesion:
- Sinonasal/orbital lesions: Nasal obstruction, facial asymmetry, epistaxis, proptosis, and visual changes (diplopia, visual impairment)[2][11]
- Jaw lesions: Painless bony expansion of the mandible or maxilla, occasionally with pain or altered occlusion[10][12]
- Skull base lesions: Headache and visual impairment are the most common presenting complaints[11]
Tempo and growth pattern
Growth is typically slow and progressive. Unlike JTOF, rapidly aggressive growth is not commonly reported for PsOF.[3] However, locally aggressive behavior—including invasion of adjacent sinuses, orbit, nasopharynx, palate, and anterior cranial fossa—occurs, particularly in larger or recurrent lesions.[2]
Complications and red flags
- Secondary aneurysmal bone cyst (ABC) development is a recognized complication, occurring more frequently in younger patients and potentially causing rapid clinical enlargement with cystic change.[3][13]
- Dural breakthrough has been documented in a substantial proportion of skull base cases.[11]
- Malignant transformation and metastasis have not been reported.[1]
Radiographic findings
Location and distribution
PsOF characteristically arises in the extragnathic craniofacial bones, with the ethmoid and frontal bones, paranasal sinuses, and orbital walls as the most common sites.[2][14] When involving the jaws, the mandibular body is the predominant location.[10][12] Lesions frequently extend across multiple anatomic compartments, particularly when centered in the sinonasal region.[2]
Periphery and shape
- Margins: Characteristically well-defined, with a thick peripheral shell of bone density visible on cross-sectional imaging. Most lesions in large series demonstrate well-defined limits on radiologic examination.[7][14][15]
- Shape: Typically round to ovoid (elliptic) and expansile. Sinonasal lesions may assume a lobulated or multiloculated configuration, particularly when associated with secondary ABC.[14][16]
- Distinction from conventional OF: Both PsOF and conventional OF have well-defined margins; however, conventional OF typically displays a thin radiolucent capsular line at the periphery on intraoral radiographs, whereas PsOF generally does not.[9]
Internal architecture
The internal density of PsOF is variable and depends on the degree of mineralization and the presence of cystic change:[1]
- Ground-glass opacity: A characteristic pattern, often presenting as an outer mantle of ground-glass density surrounding a central radiolucency, a single mural nodule, or a solid homogeneous mass.[15]
- Mixed density: The most common overall appearance in large series, with a mixture of radiopaque and radiolucent areas. Internal septations of bone density are common in sinonasal lesions.[7][10][14]
- Radiolucent: Early or predominantly cystic lesions may appear entirely radiolucent.[1]
- Target-like appearance: A concentric pattern with a dense periphery and lower-density center has been described as one of the characteristic appearances of ossifying fibromas, including PsOF.[17]
- PsOF consistently demonstrates heterogeneous internal density on cross-sectional imaging, in contrast to the more homogeneous ground-glass pattern typical of COF.[15][17]
Effects on teeth and adjacent structures
- Tooth displacement: Occurs when the lesion involves the tooth-bearing regions of the jaws.
- Root resorption: Most cases in large systematic reviews did not cause tooth root resorption.[7]
- Bone expansion: Common; the majority of both PsOF and JTOF demonstrate bony expansion.[7]
- Cortical integrity: Cortical perforation is uncommon in most series, though disruption of the overlying cortex has been documented in a minority of cases on cross-sectional imaging.[7][17]
Extent and cortical involvement
- Sinonasal lesions frequently extend into multiple sinuses and may involve the orbit, nasopharynx, palate, and anterior cranial fossa.[2]
- A thick bony wall circumscribing the lesion is a hallmark finding in sinonasal PsOF.[14]
- Dural breakthrough has been reported in a substantial proportion of skull base cases.[11]
Variants and associated findings
- Secondary ABC: When present, fluid–fluid levels within or adjacent to the expansile mass are characteristic and are best appreciated on cross-sectional imaging. The combination of an elliptic mass with ground-glass or scattered calcifications and fluid–fluid levels is highly suggestive of PsOF with secondary ABC.[13][16]
- Unilocular vs. multilocular: Most lesions are unilocular; a multilocular appearance is uncommon and is most often related to concurrent ABC.[7][9]
Other imaging findings
CT findings
On medical CT, sinonasal PsOF appears as an expansile, well-circumscribed mass bounded by a thick shell of bone density.[14] Internal content is commonly low in density with bone-density septations.[14] Scattered calcifications or a ground-glass matrix may be present.[16] When associated with ABC, mixed-density cystic areas are seen within or adjacent to the solid component.[16]
MRI findings
- Signal intensity: The bony walls appear isointense to gray matter on T1-weighted images and hypointense on T2-weighted images. The solid tumor component is typically isointense to gray matter on T1 and iso- to hypointense on T2, with heterogeneous signal overall.[14][16][17]
- Enhancement: Significant enhancement of the solid component and bony walls occurs after gadolinium administration. Dynamic contrast-enhanced MRI may show a rapidly enhancing and rapid washout pattern.[14][16]
- ABC component: Fluid–fluid levels are clearly delineated on T2-weighted images; the intracystic contents do not enhance, while the periphery and septa of the ABC show marked enhancement.[16]
- MRI is particularly valuable for evaluating orbital, intracranial, and dural involvement in skull base lesions.[11]
Differential diagnosis
PsOF shares imaging features with several fibro-osseous and osseous lesions of the craniofacial skeleton. The well-defined, expansile, variably mineralized mass centered in the sinonasal or orbital bones must be distinguished from the following entities:
| Entity | Why it is considered | Best discriminator |
|---|---|---|
| Fibrous dysplasia | Ground-glass, expansile fibro-osseous lesion of the craniofacial bones | FD blends imperceptibly with adjacent normal bone without a defined border, whereas PsOF is well-demarcated with a thick bony shell; GNAS mutation is present in FD and absent in PsOF[18][19] |
| Cemento-ossifying fibroma | Well-defined mixed-density jaw lesion with a thin radiolucent capsular rim | COF shows a peripheral radiolucent capsular line, homogeneous ground-glass density, and lacks psammomatoid ossicles histologically; SATB2 rearrangement is absent in COF[4][9][17] |
| Juvenile trabecular ossifying fibroma | Aggressive expansile jaw or maxillary lesion in a child | JTOF presents as a radiolucent lesion with irregular scattered calcifications rather than the ground-glass mantle of PsOF; histologically shows trabecular osteoid with garland-like strands rather than psammoma bodies[3][9][15] |
| Low-grade osteosarcoma | Mineralized bone-forming lesion with permeative or aggressive features | LGOS shows ill-defined margins, cortical destruction, and periosteal reaction; MDM2 amplification supports LGOS, whereas PsOF harbors SATB2 rearrangement[5][20] |
The highest-risk diagnostic pitfall is misidentification of PsOF as fibrous dysplasia, given overlapping ground-glass density and craniofacial location; the presence of well-defined margins with a thick bony shell, the absence of GNAS mutation, and the characteristic psammomatoid ossicles on biopsy are the key discriminators.[18][19]
Histopathology
Diagnostic microscopic features
The hallmark of PsOF is a densely cellular fibrous stroma interspersed with numerous small, uniform, spherical mineralized ossicles (psammomatoid bodies).[1][2] These ossicles are concentrically laminated and resemble psammoma bodies. The stroma may contain variable amounts of myxomatous material and scattered multinucleated giant cells.[2]
Distinction from other fibro-osseous lesions
- vs. JTOF: JTOF shows trabeculae of fibrillary osteoid and woven bone with a "garland-like" pattern rimmed by plump osteoblasts, rather than psammomatoid ossicles.[3][21]
- vs. COF: COF contains a mixture of bony trabeculae and ovoid cementum-like structures within variably cellular fibrous tissue; it lacks the uniform psammomatoid bodies.[9][21]
- vs. Fibrous dysplasia: FD shows irregularly shaped woven bone trabeculae ("Chinese-letter" pattern) without osteoblastic rimming, set in a less cellular stroma; osteocalcin immunoreactivity is strong in FD but weak in ossifying fibroma.[19]
Radiologic-pathologic correlation
The ground-glass density on imaging corresponds to the dense population of psammomatoid ossicles within the fibrous stroma. Radiolucent areas correlate with regions of predominantly fibrous stroma or cystic degeneration, including secondary ABC.[1][16]
Molecular findings
- SATB2 rearrangement: Recurrent SATB2 gene rearrangements (chromosome 2q33.1) have been identified in approximately 58% of evaluable PsOF cases and are absent in JTOF and COF, establishing PsOF as a genetically distinct entity.
- Chromosome 12 rearrangement: Co-amplification of MDM2 and RASAL1 on chromosome 12q has been reported in a subset of juvenile ossifying fibromas, particularly those with aggressive or recurrent behavior, without MDM2 protein overexpression.[20]
- GNAS mutation: Absent in PsOF, distinguishing it from fibrous dysplasia.[5][19]
Management and prognosis
Surgical treatment
Complete surgical excision is the treatment of choice.[1][2][7]
- Enucleation with peripheral ostectomy/curettage is recommended as the first-line approach for both JOF variants to balance adequate removal with minimization of morbidity, particularly in young patients. This approach yields lower recurrence rates than enucleation alone.[7][10]
- En bloc resection results in the lowest recurrence rates (near zero in systematic review data) but carries significant morbidity and disfigurement, especially in the pediatric population. Resection is generally reserved for large, recurrent, or anatomically complex lesions.[7][10]
- Skull base and intracranial extension may require a combined neurosurgical and transfacial approach; craniotomy (often via frontal approach) is the most common strategy for skull base PsOF.[1][11]
Recurrence
- Recurrence is a well-recognized feature of PsOF. Enucleation and curettage alone are associated with considerably high recurrence rates.[7]
- Curettage with peripheral ostectomy demonstrates an acceptable recurrence rate.[10]
- Resection virtually eliminates recurrence.[7]
- Younger patient age and concurrent ABC may be associated with higher recurrence risk.[3][22]
- Recurrence typically manifests within the first few years after surgery.[11]
Adjuvant therapy
- Radiotherapy has been reported in isolated cases for recurrent or un