# Diagnostic challenge of an arachnoid cyst mimicking hydatid cyst: a case report from Syria

## TL;DR

A case report highlights the difficulty in distinguishing arachnoid cysts from hydatid cysts in brain imaging and surgery, emphasizing the need for experienced surgeons to avoid misdiagnosis.

## Contribution

The report presents a rare case where an arachnoid cyst was initially mistaken for a hydatid cyst, emphasizing surgical dissection challenges for accurate diagnosis.

## Key findings

- Arachnoid and hydatid cysts can appear identical in radiographic and macroscopic evaluations.
- The difficulty in dissecting the arachnoid membrane is a key factor in changing the diagnosis during surgery.
- Experienced surgeons are needed to avoid misdiagnosis due to the risk of hydatid cyst rupture.

## Abstract

Cystic lesions in the brain, often seen in MRI and CT scans, may arise from various causes, including developmental issues, infections, or tumors. Differentiating between arachnoid cysts and hydatid cysts is critical for effective management, as misdiagnosis can lead to inappropriate treatments and worsen patient outcomes.

An 18-year-old right-handed female from a rural area experienced a right-sided focal seizure lasting two minutes. Her history includes progressive right-hand pain, worsening writing difficulty, persistent headaches, personality changes, and recent memory impairment. She had slurred speech. Radiological examination revealed a massive cystic lesion in the brain which initially appeared to be a hydatid cyst, but histological examination revealed it to be an arachnoid cyst.

Arachnoid cysts, comprising about 1 % of intracranial masses, are commonly found fluid-filled sacs located in the arachnoid mater, usually incidentally discovered during imaging. They are more frequent in children and males, often asymptomatic but can cause symptoms based on their location. Classification includes congenital and traumatic types, with congenital being more common. Diagnosis can be challenging, especially when symptoms overlap with conditions like hydatid cysts, complicating treatment decisions.

Arachnoid and hydatid cysts appear similar in surgery and may be hard to distinguish. Dissection difficulty should be the main way to differentiate them. A hydatid cyst diagnosis should not be ruled out until multiple attempts by an experienced surgeon have been made. Further studies are needed to clarify these findings.

•Arachnoid cysts and hydatid cysts may appear completely similar radiographically and macroscopically.•The difficulty of dissecting the arachnoid membrane is the main factor in changing the diagnosis during surgery.•The risk of hydatid cyst rupture delays diagnosis changes during surgery, which should be evaluated by an experienced surgeon.

Arachnoid cysts and hydatid cysts may appear completely similar radiographically and macroscopically.

The difficulty of dissecting the arachnoid membrane is the main factor in changing the diagnosis during surgery.

The risk of hydatid cyst rupture delays diagnosis changes during surgery, which should be evaluated by an experienced surgeon.