gms | German Medical Science

Tumours of the anterior skull base may clinically become apparent with exophthalmus, disorders of globe motility and diplopia as well as frontal cephalgia and sinusitis due to drain obstruction of the paranasal sinuses. We present an interesting case of a posttraumatic reactive fibrous bone neoformation mimicking a malignant bone tumour of the anterior skull base.

A 16-year-old male patient presented to our department with a tumour of the medial orbital roof. The tumour had been increasing in size for about one year and the boy showed exophthalmus, diplopia and disorder of globe motility. When we examined the patient, we could find a small, inconspicious scar close to the left supercilium. Exploring the history of the patient, the boy reported that a trauma in this region had preceded the tumour four years before.

A CT and MRI scan of the skull was carried out and showed a calcificated neoformation of the anterior skull base 3 to 4 cm in diameter between the anterior ethmoid cells, the left orbita and the left frontal sinus (Figure 1 [Fig. 1]). The tumour showed an unsharp demarcation, accumulated contrast medium and seemed to infiltrate the dura and to extend into the frontal cranial fossa. Furthermore the tumour-adjoining bone showed signs of reactive transformation and destruction. Because of these radiological findings and the age of the patient, the predominant tentative diagnosis at this point was in first line a malignant bone tumour of the skull base, especially osteosarcoma. As the neoformation affected the skull in a young patient, fibrous dysplasia was another clinical differential.

A biopsy of the tumour was taken via Killian’s approach. During this operation, it was noticeable that the corticalis of the bony base of the left frontal sinus was partly destroyed by the tumour, which was also adherent to the dura and showed intracranial extension. These findings underlined the tentative diagnosis of a malignant bone tumour. Nevertheless, histology showed a fibrous stroma with distinct signs of reorganisation and strong vascularisation but without any signs of malignancy. Material was also sent to the reference center for bone tumours in Basel (Switzerland), where a primary bone tumour as well as fibrous dysplasia could be excluded. The question for preceding trauma was raised, as histology showed characteristic features of a fibro-osseus reparative lesion. Taking all findings in consideration, the diagnosis of a “posttraumatic reactive fibrous bone neoformation” was made. The extirpation of the tumour was carried out by a navigated osteoplastic transfrontal sinus approach with duraplasty. Navigation support was used to control the tumour resection accurately, as the loss of anatomic landmarks and the need to resect tumour along the dura of the anterior skull base makes computer-assisted surgery a helpful instrument. Exophthalmus, diplopia and disorder of globe motility greatly improved after surgery.

Malignant bone tumours of the skull base are rare. To the best of our knowledge we describe here for the first time a “posttraumatic reactive fibrous bone neoformation” of the anterior skull base clinically mimicking malignancy, which might be an important differential in the treatment of patients with tumours of the skull base. Similar cases in other bone localisations have been described in the international literature [Ref. 1], [Ref. 2], [Ref. 3]. These bone lesions have almost exclusively been found in ribs and histopathologically described as a seperate bone tumour entity, also called fibro-osseus reparative lesion (FORL) or fibro-osseus reparative pseudotumour [Ref. 1]. Surveying the international literature for the topic of osseus and fibro-osseus lesions affecting the craniofacial bones, the authors emphasize the problem of clinically differentiating between malignant and benign lesions [Ref. 4]. Although the question of malignancy can usually be answered by histopathological investigations, fibro-osseus bone lesions are often difficult to classify on histology alone [Ref. 4]. It is the duty of the pathologist to exclude malignancy and to establish the fibro-osseus nature of the lesion. Tumour-extension has to be judged by the radiologist. It must be emphasized, that the clinician has to take all findings in consideration and that it remains an interdisciplinary challenge to establish a final diagnosis. Because of this, patient history and signs for preceding trauma must be taken into account when treating fibro-osseus tumours of the skull, as the “posttraumatic ractive fibrous bone neoformation” constitutes an important clinical differential.