3.2 Study cohort
There were 631 patients with benign histology (either salivary or
neurogenic in origin). The mean age (in years) at presentation was 42.9
± 7.76 with a median follow up of 40.98 ± 19.1 months. Baseline
characteristics and demographics along with presenting complaints,
histological variation and complications of cumulative data have been
further expressed (Table 1). The patients were categorized into two
groups based on the tissue of origin such as neurogenic (n=310) and
salivary (321), later compared on the basis of subsequent complications.
The primary surgical approached used were (i) Trans-cervical (60%),
(ii) Cervico-parotid (30%) including dissection and exposure of the
facial nerve trunk and associated branches and (iii) Trans-mandibular
(10%) comprising of mandible split for access and tumor resection
(Figure 2). Trans-cervical approach was favored in 9 out of 13 studies
as compared to 4 studies where cervico-parotid access was advocated.
None of the studies has given clear preference to the use of
trans-mandibular approach. The most common neurogenic tumor found was
schwannoma (54%) followed by paraganglioma (43%) (Figure 2). The
distribution of complications based on salivary or neurogenic histology
has been represented for all the studies included in the review.
The 148 patients with neurogenic complication among 310 neurogenic
tumors (Mean 11.38, SD 11.81) were compared against 41 patients
with neurological complication among 321 salivary gland tumors and
demonstrated significantly increased rate of nerve related complication
(t = 2.42, p <0.05) (Figure 3). Among the
neurologic complications, most encountered were vocal cords palsy
(73%), Horner syndrome (9%), hypoglossal nerve injury (6%) and first
bite syndrome (4%) (Table 2).
Factors considered for selecting surgical approaches in 13 studies on
PPS tumors were categorized into size, location, histology, proximity to
greater vessels or base of skull, histology and deep parotid lobe
involvement (Table 2). Each factor was given a score and the combined
scores were compared to the percentage of complications to assess if any
of these factors considered before surgery would have an effect in the
outcome in terms of complication rate. The correlation coefficient
suggested a small degree of positive correlation that is not
statistically significant (p=0.930) . The tissue of origin (neurogenic
vs. salivary) seems to have a positive correlation with more
complications related to neurogenic tumors (Pearson coefficient 0.662,
p=0.019) (Figure 4). The binary logistic regression showed the
significantly increased likelihood of developing post-operative
neurological complications in tumors with neurogenic histology
(p=0.0001) (Table 3).
Next we performed a meta-analysis assessing neurological complications
among the groups having salivary or neurogenic tissue of origin. Due to
heterogeneity < 50%, fixed term model was used. Data of 631
patients was available for analysis of whom 321 were of salivary tissue
origin and 310 were neurogenic in histology. Neurological deficit was
observed in 48% of patients with neurogenic histology (148/310) while
only 13% patients with salivary tumor developed neurological deficit.
The pooled RR was 2.41 (95% CI 1.80 – 3.23, p=0.001) (Figure 5).