DISCUSSION
Intradural disc herniation (IDH) is a rare phenomenon , which accounts for only 0.25 to 0.35 %[2] of all disc herniations with lumbar region being the most common site of occurrence[3]. The level most frequently affected is L4-L5 [4]. Male are more likely to have the disease entity than female. Average age of onset is between 50 -60 yrs. Symtoms of IDH may vary depending upon location of disc herniation, with cervical IDH patients presenting with clinical findings of Brown Sequard Syndrome [5], [6], or incomplete and trainsient quadriparesis and those involving lumbar region presenting as long history of radiculopathic pain with acute presentation consisting of symptoms of cauda equina syndrome [4]. In our patient both radiculopathy and cauda equina symptoms improved gradually post operatively with poor improvement of bladder function for which physiotherapy and acupuncture therapy was provided to patient.
The pathogenesis of IDH remains unclear, however few theories have been proposed. Several reports suggested that certain factors like reduced epidural space resulting from congenital or iatrogenic narrowing of spinal canal, adhesions between annulus fibrosus, posterior longitudinal ligament (PLL) and ventral dura matter were responsible for IDH [7], [8]. Among the aformentiond pathogenesis adhesion between PLL and ventral dura matter was considered to be an important factor [9], [10]. Tateiwa [11] stated that factors such as local trauma, previous spine surgery or even congenital factors like dural thickness were responsible for adhesions. Floeth and Herdmann [12] reported that chronic inflammation, as a result of degenerative disc pathologies, favors development of adhesions and lead to erosion process with thinning of the dura. Dura matter and PLL are in closest proximity at L4-L5 level which explains the highest incidence of IDH at L4-L5 level [13]. In our case, there was dense adhesion between PLL and ventral dura and we speculate that previous history of trauma with disc degeneration resulted into chronic inflammation , and during this process long term irritation, inflammation with a sudden force caused the prolapsed disc into the intradural space through the dural erosion.
A preoperative assumption and diagnosis of IDH is difficult. Lesions might be ignored or can easily be mistaken for other findings on imaging. Definite diagnosis are made only on surgery, not via imaging alone. The MRI in our case did not indicate the presence of intradural disc fragments and definitive diagnosis was made intraoperatively.