Atypical fibrous histiocytoma (AFH) is an uncommon mesenchymal neoplasm classified as an intermediate-grade fibrohistiocytic tumor (1). It most frequently arises in the dermis and superficial soft tissues of young to middle-aged adults (2). Although representing only a minor proportion of fibrohistiocytic lesions, cutaneous AFH is relatively well characterized and typically presents as a slow-growing nodular mass with low but definite potential for local recurrence (1). In contrast, primary involvement of deep soft tissue or bone is exceedingly rare, and AFH arising in the skull constitutes one of the least frequently documented presentations (3–5).

Osseous AFH, particularly within the calvarium or skull base, poses significant diagnostic difficulty (5–7). Clinical symptoms are nonspecific, and radiologic findings often overlap with those of more common osteolytic skull lesions, including giant cell tumor, Langerhans cell histiocytosis, eosinophilic granuloma, osteolytic meningioma, sarcoma, or metastatic disease (5, 7–9). Imaging typically demonstrates lytic bone destruction with variable soft-tissue extension, but these features lack diagnostic specificity, making histopathology and immunohistochemistry essential for accurate identification (5, 7). Classic microscopic features include spindle-cell proliferation, multinucleated giant cells, hemosiderin-laden macrophages, and variable atypia, accompanied by an immunophenotype generally positive for vimentin and variably reactive for CD68 (6, 7).

Only a small number of skull-based AFH cases have been reported, most involving pediatric or adolescent patients and only rarely occurring in adults (9, 10). Although gene rearrangements such as EWSR1 or FUS may be detected—more typically in angiomatoid fibrous histiocytoma—these alterations are not consistently present and are not required for diagnosis (11, 12). Owing to the scarcity of reported cases, the natural history and optimal management strategy for cranial AFH remain undefined, though complete surgical excision with adequate margins remains the primary determinant of recurrence risk (7, 10, 13).

Here, we present a rare case of primary AFH arising in the temporal bone of an adult male, manifesting with tinnitus and progressive sensorineural hearing loss. We detail the clinical course, imaging findings, surgical management, and histopathologic features of this lesion, and contextualize the case within the existing literature. This report highlights the importance of including AFH in the differential diagnosis of destructive skull lesions and underscores the crucial role of comprehensive pathological evaluation.

AFH predominantly arises in the dermis and superficial soft tissues, whereas primary involvement of bone, particularly the skull, remains exceedingly rare (7, 14, 15). To date, only a limited number of cranial or skull-based AFH cases have been reported, most of which are isolated case reports (Table 1). The earliest well-documented case of skull AFH was described by Black et al., involving an infant with a destructive calvarial lesion extending to the dura, who remained disease-free following complete surgical excision. This seminal report established the possibility of primary AFH arising within cranial bone and highlighted the importance of complete resection for favorable outcomes (5).

Subsequent reports have described fibrous histiocytoma variants involving the skull, including both atypical and benign subtypes (7). Although benign fibrous histiocytoma (BFH) is histologically and biologically distinct from AFH, several skull-based BFH cases have been reported in the parietal, temporal, and skull-base regions (7, 19, 20). These cases are relevant in the differential diagnosis, as they share overlapping imaging features such as osteolytic bone destruction and soft-tissue extension, yet generally demonstrate less cytologic atypia and lower recurrence potential compared with AFH. Inclusion of these BFH cases in the literature provides a broader perspective on fibrohistiocytic tumors of the cranial skeleton.

In recent years, angiomatoid fibrous histiocytoma—a related but molecularly distinct entity—has also been reported in intracranial and skull-base locations, including the temporal bone. These cases frequently demonstrate EWSR1-related gene rearrangements and may present with hemorrhagic or cystic components (9, 12). While molecular alterations are not consistently identified in conventional AFH, these reports underscore the histologic and genetic heterogeneity within the fibrous histiocytoma spectrum and emphasize the need for careful morphologic and immunohistochemical correlation in cranial lesions (10, 21).

Radiologically, reported skull AFH cases consistently demonstrate nonspecific osteolytic changes with thinning or destruction of the inner and outer tables and variable epidural or extracranial soft-tissue components (9, 22). Such features often lead to preoperative misdiagnoses, including eosinophilic granuloma, giant cell tumor of bone, osteolytic meningioma, metastatic disease, or plasmacytoma (9, 22, 23). MRI findings are similarly variable, with lesions typically showing iso- to hypointense signals on T1-weighted images and heterogeneous enhancement after contrast administration (9, 22). These overlapping radiologic characteristics explain why AFH is rarely considered preoperatively in cranial lesions.

Histopathologically, previously published skull AFH cases show a consistent pattern of spindle-cell proliferation arranged in fascicles or storiform architecture, admixed with multinucleated giant cells, hemosiderin-laden macrophages, and variable degrees of cytologic atypia (7). Immunohistochemistry in most reports demonstrates vimentin positivity with variable CD68 staining, while melanocytic (S100/HMB45), epithelial (cytokeratin) and Langerhans-cell (CD1a) markers are usually negative (7, 24). Rearrangements involving EWSR1 (and only rarely FUS) are well documented in angiomatoid fibrous histiocytoma and are detectable in a substantial proportion of cases, but they are not universally present and their absence does not exclude the diagnosis, which therefore remains principally morphology- and IHC-based (11, 12).

Management trends across published cases emphasize the importance of achieving complete surgical excision, as recurrence is more likely after subtotal resection (7, 25). In available reports, patients who underwent gross total resection largely remained recurrence-free, whereas those with incomplete removal demonstrated higher risk of local progression (5, 7, 26). No clear role has been established for adjuvant radiotherapy or chemotherapy in conventional AFH of the skull.

In summary, the literature suggests that although AFH of the skull is rare, its clinicopathologic features are broadly consistent with AFH at other sites, while its radiologic presentation is frequently misleading. Thorough histopathologic and immunohistochemical evaluation remains essential for accurate diagnosis, and complete surgical excision remains the cornerstone of effective management.

AFH represents an uncommon fibrohistiocytic neoplasm with intermediate malignant potential, most frequently arising in the dermis or superficial soft tissues (24, 27). Primary osseous involvement—and particularly localization in the skull—is exceptionally rare and introduces substantial diagnostic challenges for clinicians, radiologists, and pathologists (5, 7). The present case illustrates several clinically important aspects of skull-based AFH, including its nonspecific imaging appearance, histopathologic complexity, and management considerations (7, 9).

AFH of the skull is an exceptionally rare entity that poses significant diagnostic challenges due to its nonspecific clinical presentation, variable radiologic appearance, and broad histopathologic differential diagnosis. This case underscores the importance of considering AFH in the evaluation of destructive calvarial lesions, particularly when imaging findings are inconclusive and the intraoperative appearance mimics other fibro-osseous or neoplastic processes. Accurate diagnosis requires careful integration of morphology, immunohistochemistry, and exclusion of more aggressive mimickers.

Complete surgical excision remains the most effective treatment strategy and is critical for minimizing the risk of recurrence. Although the biological behavior of cranial AFH appears largely consistent with its soft-tissue counterparts, long-term follow-up is warranted due to its intermediate malignant potential. This case contributes to the limited body of literature by documenting an uncommon temporal bone presentation with associated auditory dysfunction, highlighting the need for increased awareness of this rare diagnosis among neurosurgeons, pathologists, and otologic specialists.