Spinal extradural arachnoid cysts (SEACs) are rare entities characterized by the accumulation of cerebrospinal fluid (CSF) in cysts located in the extradural space of the spinal canal¹⁷⁾. These cysts are significant due to their potential to cause spinal cord compression and associated neurological deficits¹⁷⁾. While the exact prevalence of SEACs is not well documented, their rarity is emphasized in the literature, indicating a low incidence in the general population³⁾. The etiology of SEACs is often attributed to congenital factors, acquired causes such as trauma, or iatrogenic interventions such as lumbar puncture or spinal surgery¹⁴⁾. Patients with SEACs typically present with symptoms related to spinal cord compression, which may include back pain, radiculopathy, myelopathy, and, in severe cases, neurological deficits⁴⁾. The onset of symptoms is usually gradual and correlates with cyst size and location⁴⁾. Magnetic resonance imaging (MRI) is the gold standard for diagnosis, providing detailed images of the cyst's location, size, and impact on the surrounding structures¹⁸⁾. The primary treatment for SEACs is surgical intervention, aimed at decompressing the spinal cord and nerve roots. Most patients experience significant postoperative improvement. This paper presents a case report of a 33-year-old man who fully recovered after undergoing surgical treatment for multiple SEACs at the thoracic level.

A 33-year-old man with no underlying diseases but a 2-year history of subjective lower-extremity weakness presented to our hospital with rapidly worsening symptoms, including gait disturbance and a motor grade of 4- in both legs below the hips. Hyperactive deep tendon reflexes were observed in the lower extremities.

The patient also complained of hypoesthesia around the anus and paresthesia below the umbilicus, with no fecal incontinence. MRI confirmed the presence of multiple extradural arachnoid cysts at the T5-T11 levels, compressing the spinal cord, with the cysts exhibiting the same signal intensity as CSF (Fig. 1). Computed tomography (CT) myelography revealed variations in the shading of the cyst-filled contrast agent, indicating differences between the cysts (Fig. 2). Through this radiological examination, multiple dural defects were observed, which helped make a surgical plan (Fig. 1B, C). Thoracic laminectomy was conducted from the 5th to 9th vertebrae, revealing the presence of multiple SEACs. To identify the cyst orifice, the cysts were cautiously incised, and the cystic fluid was removed. Dural defects were identified at the T6, T8, and T9 left levels.

Watertight suturing was carefully performed to repair the defects, and no CSF leakage was observed. The extradural arachnoid cyst at T10-T11 was not removed because it did not appear to contribute to neurological deficits (Fig. 3). We performed laminoplasty to prevent delayed kyphosis following laminectomy. The surgical drain was installed at the surgical site, and no CSF leakage was observed.

The day after the surgery, the patient exhibited significant improvements in lower extremity motor power (motor grade 4- to 4+), hypoesthesia around the anus, and paresthesia below the umbilicus. After a 3-month follow-up, there was a significant improvement in neurological deficits. On MRI, the cyst did not recur, and the cyst at T10-T11 that had not been removed during the initial surgery was subsequently removed (Fig. 4). Additionally, no kyphotic changes were observed on radiography.

SEACs are relatively rare, and their exact prevalence in the general population is not well documented. Some studies have suggested that they account for a small percentage of spinal space-occupying lesions (potentially approximately 1%)⁶⁾. Etiologically, SEACs are attributed to various factors, including congenital predispositions, trauma, and previous surgical interventions⁷⁾. Clinically, patients with SEACs often present with symptoms related to spinal cord compression, such as back pain, radiculopathy, and myelopathy²⁾. The severity and progression of the symptoms depend on the cyst's size and location, with larger cysts typically causing more pronounced symptoms¹²⁾. The mechanism of extradural arachnoid cyst development is unclear, but they are known to be caused by arachnoid herniation with a small defect in the dura due to congenital and acquired causes (trauma, infection, inflammation)¹⁰⁾. Three mechanisms can describe cyst enlargement. Firstly, in the case of a noncommunicating arachnoid cyst, CSF is continuously secreted from the remaining arachnoid matter. Secondly, the communicating effect, also known as the valve effect, refers to the transport of CSF into a cyst and causes intermittent increases in pressure within the extradural cyst, thereby compressing the spinal cord. Lastly, the presence of hyperosmolar cyst contents can cause an influx of free water¹⁰⁾.

Nabors et al.¹¹⁾ proposed a system that categorizes spinal meningeal cysts into three major types based on their histological and anatomical characteristics. Type 1 cysts are extradural cysts without spinal nerve root fiber involvement. These cysts do not contain neural tissue and are often referred to as “meningeal cysts.” Type 1 cysts are classified into two subtypes. Type 1a is an extradural meningeal cyst (extradural arachnoid cyst), and type 1b is a sacral meningocele (occult sacral meningocele). Type 2 cysts are extradural cysts with spinal nerve root fiber involvement, also known as "nerve sheath cysts" These cysts are associated with the nerve roots and may contain nerve fibers. Type 3 cysts are intradural cysts, which are located within the dura mater and may be associated with conditions such as Marfan syndrome or Ehlers-Danlos syndrome. SEACs are typically classified as type 1a cysts in this system because they are extradural and do not involve the spinal nerve root fibers.

The diagnosis of SEACs relies on advanced imaging techniques such as MRI because of their ability to provide detailed images of cysts, including their size, location, and relationship with adjacent neural structures¹⁴⁾. A study documented that MRI can detect the presence of pulsatile turbulent flow disruptions at a faulty site in CSF dynamics¹⁾. Complementing MRI, CT myelography is often employed, especially when MRI results are inconclusive¹⁾. CT myelography, which involves the injection of a contrast medium into the spinal canal followed by CT imaging, is adept at visualizing the impact of the cyst on the spinal canal and nerve roots, and it can help identify dural defects²⁾. In this case, multiple orifices were identified through MRI and CT myelography; thus, planning for cyst resection and dural repair could be executed through laminectomy at multiple levels. It is crucial to identify the location of the orifice in preoperative imaging. In addition to MRI and CT myelography, various techniques such as MR myelography, cine-MRI, and kinematic MRI have been explored in order to improve the accuracy of orifice detection^2,16). Additionally, electrodiagnostic studies, such as electromyography and nerve conduction studies, can be useful, particularly for assessing the functional impact of cysts on the spinal cord and nerve roots in cases presenting with symptoms such as radiculopathy or myelopathy⁵⁾. This comprehensive diagnostic approach, integrating various imaging and functional assessment tools, is crucial for accurately diagnosing SEACs and guiding effective treatment planning¹⁵⁾. Regular follow-up with MRI is recommended to assess any signs of recurrence¹³⁾.

The primary treatment approach for SEACs is surgical intervention, particularly when the cysts are symptomatic¹⁴⁾. The goal of surgery is to alleviate the compression of the spinal cord or nerve roots, thereby relieving symptoms and preventing further neurological deterioration⁸⁾. There are two surgical methods: total cyst resection, and surgery to close the canal between the subarachnoid and extradural cysts⁴⁾. There are also reports indicating that recurrence may occur if total resection is not performed⁷⁾. However, dealing with a large cyst may necessitate multiple laminectomy procedures for removal, potentially causing damage to the back muscles or altering alignment⁴⁾. However, some reports suggest that blocking the canal does not significantly differ in recurrence compared to total resection¹⁴⁾. In our case, long-level laminoplasty was performed. Laminoplasty can minimize kyphotic changes and serve a protective function. Additionally, in the event of recurrence, it prevents dural adhesion, making reoperation more feasible.

The prognosis of patients with SEACs after surgical intervention is generally favorable⁹⁾. Most patients experience significant postoperative symptom relief and improvements in neurological function⁵⁾. However, there is a risk of recurrence, necessitating long-term follow-up¹⁵⁾. Early surgical intervention prevents permanent neurological damage and improves overall outcomes.

SEACs require detailed imaging for tailored surgical strategies, emphasizing the importance of MRI and CT myelography. The combination of laminoplasty with laminectomy helps preserve spinal alignment and simplifies future interventions if cysts recur. This approach underscores the significance of precise radiological planning in enhancing surgical outcomes for SEACs and highlights its critical role in managing these rare conditions.