# Unilateral mandibular condylar hyperplasia with ipsilateral masticator muscle and parotid gland hypertrophy: a rare incidental finding on brain MRI

## TL;DR

A rare case of jaw growth disorder was identified through brain MRI, showing how swelling in the parotid gland can mask underlying skeletal issues.

## Contribution

This case highlights the importance of quantitative MRI analysis in diagnosing unilateral mandibular condylar hyperplasia masked by parotid gland swelling.

## Key findings

- MRI revealed a 31% left condylar height asymmetry and significant hypertrophy of the left masseter and medial pterygoid muscles.
- Parotid gland swelling was found to be a primary presenting feature of unilateral mandibular condylar hyperplasia.
- Early diagnosis through quantitative volumetric analysis allowed for a 6–12 month window for intervention before symptoms developed.

## Abstract

Mandibular condylar hyperplasia (MCH) is a rare developmental disorder characterized by excessive growth of the mandibular condyle, leading to facial asymmetry, functional impairment, and dental malocclusion. Early radiological identification is essential for timely intervention, particularly when parotid gland involvement masks the underlying skeletal pathology.

A 15-year-old male presented with an 8–9 month history of painless left parotid swelling. MRI revealed a unique triad comprising a bulky left parotid gland measuring 4.3 × 3.2 cm compared to 3.1 × 2.4 cm on the right, left masseter hypertrophy with a volume of 28.3 cm³ versus 18.7 cm³ on the right representing a 51% increase, and left medial pterygoid hypertrophy measuring 15.2 cm³ versus 10.1 cm³ on the right showing a 50% increase. Quantitative analysis demonstrated significant left condylar enlargement with 31% height asymmetry, measuring 24.3 mm on the left versus 18.5 mm on the right, and increased anteroposterior diameter of 11.2 mm versus 8.3 mm. SPECT imaging was performed to assess growth activity, guiding subsequent management decisions between immediate surgical intervention versus conservative monitoring.

This case demonstrates how unilateral condylar hyperplasia can present primarily as parotid swelling, potentially misdirecting clinical attention. Quantitative volumetric analysis proved essential for diagnosis. The documented 31% condylar asymmetry with preserved function illustrates effective neuromuscular compensation, providing a 6–12 month window for intervention before symptom development. Early multidisciplinary collaboration is crucial for optimal outcomes.