Clinical History
A fifteen year old boy presented with a clinical history of several months of weakness and clumsiness in the left extremities with left upper limb paresthesia. Upon physical examination, hyperactive deep tendon and extensor plantar reflexes were found in the left limbs.
Imaging Findings
The patient underwent brain magnetic resonance imaging (MRI) which was completely normal, as well as spinal MRI that revealed at the level of the second and third vertebral bodies a well delimited oval shape lesion located in the spinal canal, anterior and left to the spinal cord, causing a widening of the subarachnoid space and contralateral displacement of the spinal cord, that was compressed. The lesion was homogeneously hypointense on T1WI and hyperintense on T2WI and showed no enhancement after contrast administration, signal intensity similar to that of the cerebrospinal fluid (CSF).
Discussion
Intradural arachnoid cysts (AC) can be classified as a type III meningeal cyst according to Nabors’s et al. classification (1), which usually arises as anomalies of meningeal development. It also can be acquired and probably causes include hemorrhage, infection, trauma and surgery. They are a rare cause of spinal cord compression, most frequently located in the dorsal spine and with an estimated 15% located in the cervical spine. Only a small number of cases have been reported ventral to the spinal cord in absence of a history of trauma, infection or hemorrhage (1, 2). In the majority of cases they are found dorsal to the neural elements. They may be single or multiple. Men and women are equally affected, often between the third and fifth decades of life (2).
Symptoms and signs are variable and non-specific (1). The most common presenting symptom is back pain, followed by sensory changes and weakness. An intermittent course of the clinical symptoms is typical, and sometimes the clinical misdiagnosis of multiple sclerosis could be made (2).
Nowadays MRI has become the diagnostic procedure of choice because is non-invasive and allows a well detailed anatomic visualization. It is also useful for demonstrating chronic myelopathy and other abnormalities associated (2).
The characteristic MRI finding of intradural AC is a spinal space-occupying mass with T1 and T2 weighted signal identical to that of the CSF, because of which they are poorly delineated, opposite to those located in the epidural space that are clearly demarcated within the epidural fat. Widening of the CSF space on MRI and displacement and thinning of the spinal cord may be the only sign of intradural arachnoid cyst (2).
CT myelography is one of the modalities available for the diagnosis, and cases can be divided into three groups: the most frequents with direct communication with the CSF, showing immediately spontaneous contrast filling; those completely isolated from the CSF circulation presenting as filling defects and those which initially presents as filling defects but would fill with contrast if imaged later within 12-24 hours (2).
Surgery is the treatment of choice. Complete excision or wide fenestration of the subarachnoid membranes is performed. In case of recurrence aggressive excision, fenestration or shunting into the peritoneal cavity has been effective.
Differential Diagnosis List
Pathologic study of the surgical piece revealed an arachnoid cyst.
Epidermoid cyst (EC) can have the similar appearance on conventional MRI sequences
but the apparent diffusion coefficient is restricted because of the squamous epithelial cells within the cyst
opposite to AC. This differentiation is important because the goal in EC is complete excision (3).
.
Final Diagnosis
Pathologic study of the surgical piece revealed an arachnoid cyst.
