This study critically assessed the possibility of tumour spread along the inferior alveolar nerve (IAN) and its sensitivity as an intraoperative marker for clear bony margin control in frozen section during segmental mandibulectomy. Fifteen patients with oral squamous cell carcinoma (OSCC) involving the mandible and requiring a segmental mandibulectomy were included in this prospective trial. The ends of the IAN were analyzed using quick section analysis and the results compared with those of the definite pathological report. Nerve tissue could be identified in 25 of the 27 specimens collected. No specimen revealed tumour invasion. All histological diagnoses were finally confirmed. Three positive bony margins with microscopic carcinoma infiltrates were found, whereas corresponding nerve tissue did not confirm tumour invasion. This study supports the assumption that the pattern of tumour invasion is rarely primarily along the IAN in OSCC involving the mandible. Quick section analysis of the nerve tissue alone is therefore not a valid marker for intraoperative bony margin control. However, it can be used as an additional intraoperative diagnostic tool combined with other methods in rare cases of primary tumour spread along the IAN. A review of current knowledge regarding bony margin control published in the literature is provided.
Oral squamous cell carcinoma (OSCC) is a serious and increasing problem in Western and Asian countries. The 5-year survival rate is 59.4%, and this entity is responsible for 8000 deaths per year in the USA and has become the fifth most common malignant tumour affecting the male population. Apart from lymph node involvement, the prognosis is dependent on tumour size, and overall survival is impacted when jaw bone infiltration occurs. The prevalence of mandibular bone involvement by OSCC is reported to range from 11% to 56% of cases. Intraoperative evaluation of the soft tissue margins of OSCC is performed routinely by quick section analysis of samples obtained by frozen section technique. However, only a few studies have focused on the analysis of frozen bone sections during segmental mandibulectomy and the results have varied widely. Thus no reliable technique for routine clinical use has been identified to date.
Simultaneous reconstruction after segmental mandibulectomy is desirable as it improves quality of life. However, reliable investigation of the osseous margins requires tissue decalcification, which can take up to 14 days. This time frame is critical if immediate free flap reconstruction has been performed and further bone resection is necessary due to unexpected tumour invasion.
There appear to be no existing data on the average amount of resected tumour-free bone, because routine clinical practice involves the pathologist evaluating cross-sections of the distal and proximal ends and the adjacent 5 mm of bone to classify the margins as clear. Different methods for sampling and processing bone specimens for quick section analysis are reported in the literature. Only very few of them are used regularly in the clinical routine, mainly due to a lack of technical expertise or equipment.
Perineural invasion (PNI) or perineural spread (PNS) in OSCC, as well as in early lesions, has been emphasized as a very important prognostic factor, especially in relation to the inferior alveolar nerve (IAN). Therefore its role in tumour spread has been the subject of intense debate. While several authors dispute its role as a preferred route of tumour extension and have indicated that this phenomenon is an uncommon finding, others have shown cases of preferential spread along the IAN. Many authors have examined the prognostic value of clinically evident positive PNS with neurological disturbances in the case of extended OSCC. The perineural space lies between the enclosing protective nerve sheath and axons and is thought to enable some invasive malignant neoplasms to spread to distant sites through a pathway of reduced tissue resistance. As there are reported cases of free bony margins but infiltration of the IAN on the contralateral side of the mandible, it is possible from the theoretical point of view that the nerve might be a sensitive marker for tumour invasion of the mandible, predominantly in cases with tumour spread along the IAN.
Therefore, the aim of this prospective feasibility study was to critically evaluate whether a marginal IAN biopsy is representative of the complete mandible margin in certain cases. Furthermore it was sought to answer the question of how often the IAN is the dominant route of tumour entry and spread within the mandible and could therefore be used in these high-risk cases as a reliable and feasible additional marker to evaluate bony margins during the segmental resection of OSCC.
Materials and methods
All patients included in this study had OSCC in direct contact with the mandible as determined clinically and radiologically (multi-slice computer tomography). None of the subjects had any signs of numbness of the lower lip. Apart from the segmental mandibulectomy due to mandibular bone infiltration, all patients with a T3/T4 status who were pN0 underwent an ipsilateral selective neck dissection with clearance of the level I–III nodes, in accordance with the German guidelines for oral cancer. In the case of metastatic nodal disease (pN1 or pN2) that was confirmed intraoperatively by frozen section, a modified neck dissection with extended nodal clearance down to level IV and V and a contralateral neck dissection at levels I–III was done. Postoperative radiotherapy or radiochemotherapy was administered if indicated according to the German guidelines for oral cancer. To obtain a homogeneous sample, subjects who had undergone preoperative radiotherapy or chemotherapy, showed any gap between the mandible and tumour, and those with a poor prognosis for any reason were excluded from the study.
Preoperative diagnosis included the histological confirmation of the clinical diagnosis (if not already performed by the transferring dentist or surgeon), panoramic X-ray, computed tomography (CT), magnetic resonance imaging (MRI), and single photon emission computed tomography (SPECT)/CT performed according to a previously published protocol. Written informed consent for clinical and imaging diagnostic modalities, as well as for tissue biopsies for diagnostic and research purposes, was obtained from all patients at the time of initial presentation. The study was approved by the ethics committee of the hospital. Study subjects were enrolled in a clinical protocol reviewed and approved by the institutional cancer board according to the German and European guidelines for oral cancer treatment. During the segmental bone resection, a margin of at least 10 mm from the macroscopically suspected bone area was included ( Fig. 1 A) .
Immediately after bone resection, a representative sample was taken from the distal and proximal (if present) part of the IAN, which was sent for quick section analysis ( Fig. 1 B–D). The IAN tissue was prepared in a routine way by frozen section and cutting with a microtome. The complete specimens were analyzed further using paraffin embedding and staining ( Fig. 2 A, B ). Quick section analysis findings were compared with the definite histopathological results as the ‘gold standard’ regarding invasion of the nerve tissue. Based on the histological results of the resected specimens, a 2 × 2 contingency table was constructed to calculate sensitivity and specificity.
Fifteen patients were treated with curative intent by segmental mandibulectomy due to extended OSCC adjacent to the lower jaw or because of clinically visible or radiologically proven infiltration ( Table 1 , Fig. 1 A). Reconstruction was performed with a fibula free flap ( n = 7), or with an anterolateral thigh (ALT) or deep inferior epigastric artery perforator (DIEP) flap combined with a reconstruction plate (ALT, n = 7; DIEP, n = 1) ( Table 1 ).
|Characteristics||OSCC ( n = 15)|
|Age, years, median (range)||61 (43–79)|
|Second-look resection intraoperatively (soft tissue)||4|
|Fibula free flap||7|
|Reconstruction plate + ALT flap||7|
|Reconstruction plate + DIEP flap||1|
Nerve tissue of the IAN could be identified in 25 of the 27 specimens collected. None of the nerve tissue specimens showed tumour infiltration. The specimens in which nerve tissue could not be identified revealed soft tissue without tumour invasion. There was no false-positive reporting of the IAN. The accordance was 100% when comparing quick section analysis with the definite final histology of the IAN and the full cross-sections of the mandibular bone margins ( Fig. 2 A). All bony and soft tissue margins were tumour-free, except in one patient with microscopic anterior and posterior residuals and one patient with posterior residuals. The corresponding nerve tissue revealed no tumour tissue in any specimen, but atypical cells with chronic inflammation were seen in the nerve specimens of the patient with microscopic anterior and posterior residuals. There was a need for further resection of the soft tissue within the same operation in four cases.
If the presence of atypical cells in the specimens was included in the assessment, the sensitivity of quick section analysis was 67%; if only manifest tumour cells in the IAN were considered, the sensitivity decreased to 0%. Primary tumour spread along the IAN could be shown in only one case. As a consequence of these results, quick section analysis of the nerve tissue alone is definitely not a valid marker for intraoperative bony margin control. It could be used as an adjunctive tool selectively for those rare cases with primary PNI of a bone-infiltrating OSCC, who mostly already show numbness of the lower lip at the time of primary diagnosis. By using this procedure selectively in the latter small sub-sample, the intraoperative certainty of clear bony margins could be increased and overtreatment of false-positive cases could also be avoided. This can be a risk if planning of the resection is based only on preoperative imaging modalities ( Fig. 3 ).