A rare clinical challenge: Desmoplastic Fibroma and Tuberous Sclerosis Complex

Imagine a 12-year-old female patient, followed for tuberous sclerosis complex (TSC) and stabilized on carbamazepine (200 mg), presenting with a painless mandibular swelling that had been evolving for two years. This exceptional clinical case confronts the practitioner with the rare co-occurrence of a desmoplastic fibroma (DF) within a TSC context. Although benign, DF is characterized by formidable local aggressiveness and a high recurrence rate, reaching 37 to 72% after simple curettage. This study documents the management of an expansive lytic lesion measuring 5.2 x 4.1 x 3.8 cm that caused bicortical deformation and significant dental displacement.

The objective of this report is to detail the surgical strategy of segmental resection and rigid stabilization adapted for a growing child. Beyond the technical procedure, the authors examine the pathogenic link between these two entities: the central hypothesis is based on the deregulation of the mTOR signaling pathway, linked to TSC, which could promote this mesenchymal proliferation. For the oral surgeon, the challenge is to validate an immediate radical approach to prevent recurrence while planning for long-term aesthetic and functional rehabilitation.

Therapeutic protocol and investigations

This case report details the management of a 12-year-old female patient with tuberous sclerosis complex (TSC) treated with carbamazepine (200 mg). The mandibular lesion, which had been evolving for two years, was the subject of a targeted diagnostic and surgical protocol.

The methodology is based on the following interventions:

• Imaging assessment: The 3D scanner identifies a 5.2 × 4.1 × 3.8 cm osteolytic lesion with bicortical expansion. The MRI shows a low signal intensity on T2 and STIR sequences, characteristic of fibrous stroma.
• Histopathological analysis: A prior incisional biopsy reveals dense collagen bundles and spindle-shaped fibroblasts without nuclear atypia or necrosis.
• Surgical procedure: The surgeon performs a segmental mandibular resection under general anesthesia with nasotracheal intubation. The excision includes all bone segments carrying the tumor.
• Functional rehabilitation: The operator stabilizes the bone defect using a 2.5 mm thick titanium reconstruction plate with 20 holes.
• Fixation system: 2.5 mm × 8 mm bicortical screws fix the osteosynthesis material to the residual mandibular segments.

The surgical team confirms tumor-free margins during the final histopathological examination. Given the patient's age and residual growth, the practitioners postpone definitive bone reconstruction until skeletal maturity.

Parameter	Clinical and radiological observation
Maximum dimensions	5,2 x 4,1 x 3,8 cm
Location	Left mandible (molar sector towards the anterior third)
MRI signal (T2 / STIR)	Hyposignal (characteristic of an intraosseous fibrous nature)
Mass effect	Displacement of teeth 32 to 36 and cortical thinning

Definitive bone reconstruction was deferred, a prudent decision dictated by the patient's young age and residual mandibular growth. This case highlights the need for a multidisciplinary approach combining head and neck oncology and maxillofacial surgery to manage these locally aggressive tumors in a complex systemic context.

Case analysis and clinical implications

This observation highlights the complexity of managing a desmoplastic fibroma (DF) in a patient with tuberous sclerosis complex (TSC). Although the literature does not establish a formal causal link, the deregulation of the mTOR pathway, characteristic of TSC, could theoretically promote this mesenchymal proliferation. The diagnostic challenge here lies in the rarity of this co-occurrence and the local aggressiveness of DF, which necessitates a rigorous therapeutic strategy.

The choice of segmental resection with clear margins addresses the major risk of local recurrence of DF, historically documented between 37% and 72% following simple curettage. Magnetic resonance imaging (MRI) played a decisive role by revealing a low signal in T2 and STIR, immediately pointing towards the fibrous nature of the lesion. This radiological specificity, correlated with a bicortical expansion visible on the CT scan, allowed for the planning of a radical intervention rather than a conservative approach, which is often insufficient.

L'utilisation d'une plaque de reconstruction en titane de 2,5 mm sécurisée par des vis bicorticales assure la stabilité structurelle immédiate. Cette approche privilégie le rétablissement des fonctions essentielles et de la symétrie faciale chez cette jeune patiente de 12 ans. Toutefois, l'étude présente une limite intrinsèque : en tant que rapport de cas unique, elle ne permet pas de généraliser le lien pathogénique entre TSC et FD, ni de garantir l'absence de récidive sans un suivi à très long terme.

Summary of results

This clinical case details the management of a 12-year-old female patient with tuberous sclerosis complex (TSC) presenting a mandibular desmoplastic fibroma measuring 5.2 x 4.1 x 3.8 cm. The intervention consisted of a segmental resection stabilized by a 2.5 mm titanium reconstruction plate fixed with 8 mm bicortical screws, allowing for immediate functional rehabilitation while deferring bone reconstruction until skeletal maturity.

In concrete terms, for the practitioner:

• Radical surgical choice: Systematically prioritize segmental resection with healthy margins over curettage, in order to counteract a high local recurrence rate (37% to 72%).
• Growth management: In young patients, use a rigid reconstruction plate to maintain space and occlusion, but defer the definitive bone graft to avoid hindering residual mandibular growth.
• TSC Vigilance: In the presence of a tuberous sclerosis complex, remain attentive to rare mesenchymal proliferations such as desmoplastic fibroma, possibly promoted by the deregulation of the mTOR pathway.

Technical lexicon of the study

Desmoplastic fibroma: Rare and locally aggressive intraosseous fibrous tumour, histologically characterised by abundant collagen fibres and spindle-shaped fibroblasts, with a high propensity for local recurrence.

Tuberous Sclerosis Complex (TSC): Autosomal dominant neurocutaneous syndrome caused by mutations in the TSC1 or TSC2 genes, leading to activation of the mTOR pathway and the development of hamartomas in various organs.

Bicortical expansion: Tumor growth phenomenon resulting in simultaneous thinning and displacement of the buccal and lingual bone plates, characteristic of expansive mandibular lesions.

mTOR pathway (mammalian target of rapamycin): Intracellular signaling pathway whose dysregulation is central to TSC and which could contribute to the mesenchymal proliferation observed in desmoplastic fibroma.

Segmental mandibular resection: Surgical procedure consisting of the complete excision of a bone segment bearing the tumor with healthy margins, preferred to limit the risks of local recurrence (estimated between 37% and 72% after curettage).

Reconstruction plate (2.5 mm): Rigid titanium osteosynthesis device, fixed by bicortical screws, used to ensure immediate stabilization of the mandibular defect and restore the continuity of the arch after resection.

Calcified subependymal nodules: Neurological manifestations characteristic of tuberous sclerosis complex, identifiable by brain imaging (CT) to confirm the diagnosis of neurocutaneous syndrome.

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