Desmoplastic (collagenous) fibroma of the parietal bone: Case report and review of the literature

Imaging

Computed tomographic (CT) brain and bone window with 3D reconstruction showed a 2.5 × 5 × 5 cm extracranial heterogeneous mass with a soft-tissue component and hyperdense calcification based on the left parietal bone. The lesion did not invade the diploe, as shown in Figure 1a-g. Cerebral CT angiography (CTA) showed blood supply from temporal artery branch [Figure 1h].

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Figure 1:

Axial and coronal computed tomography (CT) brain and bone window with 3D reconstruction showing a 2.5 × 5 × 5 cm extracranial heterogeneous mass with a soft-tissue component and hyperdense calcification based on the left parietal bone. The lesion did not invade the diploe. Brain CT angiography (CTA) showing blood supply from temporal artery branch. (a and b) Axial CT brain window. (c and d) Axial CT bone window. (e and f) Coronal CT brain and bone window. (g) 3D reconstruction. (h) CTA.

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Magnetic resonance imaging (MRI) of the brain revealed a heterogeneous mass based on the left parietal bone that was isointense on T1-weighted image and slightly hypointense on T2-weighted image, and inhomogeneously progressive enhanced on postcontrast T1-weighted image. The multiple hypointense areas in the central regions of the lesion on T1- and T2-weighted images suggested calcification [Figure 2a-m].

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Figure 2:

Magnetic resonance imaging of the brain revealing a heterogeneous mass based on the left parietal bone that was isointense on T1-weighted image and slightly hypointense on T2-weighted image, and inhomogeneously progressive enhanced on postcontrast T1-weighted image. The multiple hypointense areas in the central regions of the lesion on T1 and T2-weighted images suggested calcification. (a-d) T2W, T1W without contrast, T2 weighted-Fluid-attenuated inversion recovery (T2-FLAIR) and T1W with gadolinium mid-axial image. (e-h) T2W, T1W without contrast, T2-FLAIR and T1W with gadolinium upp-axial image. (i and j) T1W sagittal image without contrast. (k and l) T1W sagittal image with gadolinium. (m) T1W coronal image with gadolinium.

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The radiological differential diagnoses included hemangioma, hemangiopericytoma, invasive meningioma, and metastasis.

Management

The patient underwent surgical removal of the tumor. During the operation, a white, tough texture, locally hard and ossified tumor with insufficient blood supply was found to be adherent to the outer table of the skull. The tumor was separated from the surrounding tissues and cut into blocks. The remaining part attached to the skull was removed with a bone chisel and ground with a drill [Figure 3]. The surgery went smoothly, and the patient returned to the ward safely after the surgery.

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Figure 3:

Post-operative axial computed tomography (CT) brain and bone window showing complete excision of the lesion and curettage of the attached part of skull. (a) Axial CT brain window. (b) Axial CT bone window.

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Pathology

The gross specimen consisted of multiple irregular pieces of firm, gray-white tissue, with areas of ossification. After partial decalcification of the tissue, routine histological examination was performed. Microscopic examination revealed that spindle and star shaped fibroblasts within abundant collagen or collagen myxoid stroma background, with sparse blood vessels and no obvious cellular atypia or nuclear division. There was not clear between the lesions with bone tissue. The final diagnosis was DF (collagenous fibroma) [Figure 4].

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Figure 4:

Hematoxylin and eosin staining showing spindle and star shaped fibroblasts within abundant collagen or collagen myxoid stroma background, with sparse blood vessels and no obvious cellular atypia or nuclear division (magnification, ×200).

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Regular follow-up over 17 months revealed no local recurrence.

Clinical perspective

DF stands as an exceptionally rare tumor, accounting for <0.1% of all primary bone tumors.^[10,29-31] While it can manifest in any bone, the long bones, particularly the distal femur and proximal tibia, are commonly affected; however, its predilection for the mandible in the skull context is noteworthy.^[32,33] The occurrence of DF in the cerebral cranium is extremely rare, with Gardini et al. first describing it in 1978,^[1] and only 31 cases have been reported to date. This study presents the inaugural primary case featuring a rapid increase during pregnancy, accompanied by distinct imaging findings not typical in prior cases.

The literature review highlights the temporal bone as the most frequently affected site, followed by the frontal and parietal bones.^[18] In this series, the occipital bone exhibited the least impact (1 case). There is no consistent preference among frontal (11 cases), parietal (10 cases), and temporal bones (10 cases).

Divergent perspectives exist in the literature concerning the incidence rate across genders and ages of DF in bone. Initial research suggested no gender predilection,^[34] while subsequent studies, such as Kamata et al.,^[35] reported a male predominance. DF of the mandible showed a slight female predilection.^[36,37] Notably, DF of the cerebral cranium exhibited a marked female predilection in this review (22 cases in women vs. nine cases in men, with gender unavailable in one case).

Despite the elderly woman in the previously cited publication,^[35] DF of the bone typically occurs in the 3^rd decade.^[29,34,38] In the 32 cases of DF in the cerebral cranium [Table 1], ages ranged from birth to 86 years old. The majority (24/31, 77.4%, with no available age in one case) occurred in the first three decades, consistent with prior research.^[39] The frontal and parietal bones exhibited a higher predilection before the age of 30 (10/11, 91%, mean age 11.2-years-old, and 9/10, 90%, mean age 23.1 years old, respectively). Temporal bone lesions manifested at a relatively older age,^[27] with 5 cases (5/9, 55.5%, mean age 41.4 years old, with no available age in one case) reported after 40 years old.

Clinical presentations of DF in the cerebral cranium often include a palpable mass on the head, colloquially referred to as “a lump in the scalp,”^[24] and/or headaches. Temporal bone lesions may cause additional symptoms such as aural fullness, hearing loss, and ear drainage.^[7,10,12,20] While there have been no reports of permanent facial paresis or paralysis, transient facial paresis has been documented.^[23] Uncommon symptoms involve recurrent afebrile seizures in a child,^[24] and some cases are discovered incidentally.^[8] The duration of symptoms varies widely, ranging from several weeks to 15 years, with one case being congenital.^[15] Triantafyllou et al. suggested a potential hormonal dependence of DF and reported a case exhibiting rapid tumor proliferation during pregnancy.^[40] In our case, the notable increase in the lesion during pregnancy further supports the potential hormonal influence on DF progression.

Imaging

Exploring the imaging features of DF within the cerebral cranium reveals a domain still awaiting widespread recognition due to the limited corpus of published studies. Radiographically, DF in the cerebral cranium typically manifests as a solitary, lytic lesion, occasionally with a mild sclerotic margin^[17,20] or without a margin.^[6,11,14] CT and MRI play key roles in determining the extent of bone destruction.^[31]

On CT, DF in the cerebral cranium often presents as a well-defined, solitary, lytic lesion, and with or without diploic space expansion.^{[5,12,17,18,25]} The outer and inner skull tables may show thinning or even cortical breakthrough,^{[16,21,24,26]} sometimes creating a distinctive beveled edge due to uneven destruction of the inner and outer tables.^[2] A central soft tissue with mild, heterogeneous enhancement is frequently observed.^[13] Notably, these tumors can extend into the soft tissues of the scalp and underlie the dura.^[15] In our case, a unique extracranial, heterogeneous hyper-dense lesion with a soft-tissue component based on the outer tables is evident, without involvement of the diploic space and inner tables, a pattern seldom reported in the literature.^[28] A notable case by Dadlani et al. shares resemblance.^[22] The extended 15-year history showed a giant sclerotic lesion with “sun ray” spicules and a substantial soft-tissue component, causing erosion of the diploic space and inner tables, ultimately inducing compression of the brain parenchyma.

MRI findings are less specific, with only 16 of the 31 cases providing MR data. However, these features exhibit considerable heterogeneity. Commonly described are intradiploic lytic masses with soft-tissue involvement. T1-weighted images usually depict hypointensity^[9] or isointensity,^[8,20] while T2-weighted images demonstrate heterogeneous hypointensity^[12,14] to slightly hyperintensity.^[8,16] Contrast-enhanced MRI reveals diverse enhancement patterns, including moderate enhancement^[8] and homogeneous or heterogeneous significant enhancement.^{[9,12-14,17,24]} Our case aligns with a CT appearance reported by Elbadawy et al. yet diverges in MR findings.^[28] In our instance, the soft-tissue component appears slightly hypointense on T2-weighted images with heterogeneous progressive moderate enhancement. Notably, this contrasts with marked hypointensity on T2-weighted images without enhancement. Importantly, none of the previously reported cases have shown invasion into the brain parenchyma.

Given the non-specific imaging characteristics, radiological diagnosis alone is challenging, emphasizing the need for pathological confirmation.^[6]

Treatment approaches and recurrence patterns

In an insightful exploration by Böhm et al.,^[29] a meticulous investigation into DF recurrence rates following various treatment modalities was conducted. The outcomes underscore a notable disparity, revealing a higher recurrence rate (55%) in patients subjected to curettage. In stark contrast, patients undergoing resections exhibited a substantially lower recurrence rate (17%). Impressively, among those who underwent wide resections with a minimal follow-up of 3 years (mean 6.1 years), no recurrences were reported in 11 cases.

The findings strongly advocate for the indispensability of complete resection with a wide margin in averting recurrence, particularly when juxtaposed with DF occurrences in other anatomical sites. Within the purview of our review, surgical resection emerges as the predominant and favored treatment paradigm for nearly all patients. Follow-up durations ranged from 3 months to 6 years, revealing a reassuringly low recurrence incidence. Remarkably, only a singular patient exhibited recurrence merely 4 months post-surgery^[24] in contrast to the comparatively elevated recurrence rates observed in DF affecting long bones.^[41] In this exceptional case, the recurrent mass was successfully eradicated at 10 months postoperatively, with coagulation of the surrounding dura mater. Encouragingly, no signs of recurrence surfaced even 12 months after the second craniotomy.

Regarding the dura, prior cases in our review delineate a prevalent trend wherein most patients did not receive specific treatment for the dura,[1-9,11,13,16-23,26,27] with exceptions for four lesions where treatments included extensive dural resection and partial dural coagulation, electric and chemical cauterization, and dural excision and duroplasty.^{[10,12,14,15]}

The realm of potential adjuvant therapies for DF remains underexplored, with endocrine therapy employing tamoxifen showing promise, particularly in young patients.^[7] However, the broader efficacy of adjuvant therapies, encompassing radiotherapy or chemotherapy, remains inconclusive.^[20] Notably, radiotherapy assumes significance as a plausible alternative therapy if en bloc resection is not feasible.^[42]