An annular fissure or tear is a deficiency of one or more layers of the annulus fibrosus.
Most annular fissures are asymptomatic, but some may be painful. Typically, simple symptomatic annular fissures without disc herniation are treated with non-steroidal anti-inflammatory medications and low-impact physical therapy. Chronic pain due to annular fissures can be due to granulation tissue or in-growth of nerve endings which is usually seen near the dorsal root ganglion. Additionally, an annular fissure can allow extrusion, for example, disc herniation, of the nucleus pulposus and compress the adjacent nerves.
The annulus fibrosus is the type I collagen surrounding the nucleus pulposus in approximately 15-20 layers. Together the annulus fibrosis and nucleus pulposus form the intervertebral disc between adjacent vertebrae. The annulus fibrosus runs obliquely between edges of adjacent vertebrae, connecting the inferior endplate of the superior vertebra with the superior endplate of the inferior vertebra. The directions of the layers of the annulus fibrosus alternate which adds to the strength of the annulus fibrosus. Near the central region, the annulus fibrosus blends with the nucleus pulposus. The posterolateral aspect of the annulus fibrosus has a greater content of vertically oriented fibers leading to relative focal weakness at the posterolateral aspect. This anatomy of the annulus fibrosus explains why most annular fissures are at the posterior or posterolateral aspect of the annulus fibrosus.
Annular tears are commonly identified in asymptomatic individuals during imaging for other reasons. Estimates for annular tears in adults range from a few percent to upward of 50% depending on the criteria and imaging used to identify an annular tear.
The posterolateral aspect of the annulus fibrosus has a greater content of vertically oriented collagen fibers. In other regions of the annulus fibrosus layers are alternating obliquely oriented layers. Thus in the postero-lateral region, the vertical alignment of the fibers is more likely to allow for focal deficits of the annulus fibrosus and tearing or separation between the vertically oriented fibers.
Most annular fissures or annular tears are asymptomatic and discovered incidentally on imaging. If an annular fissure or tear is symptomatic, it may cause one of two findings: localized pain secondary to the tear or radicular symptoms secondary to irritation of the passing nerve root. The pain may either be acute if the tear occurs suddenly or more chronic if there is the slower development of the annular fissure.
If the annular fissure is locally symptomatic it may cause pain localized deep pain worse with movements which can stress or irritate the focal annular tear. In such cases, there is no radicular nerve involvement, and the physical exam may be unrevealing. Sometimes the annular tear can irritate the transversing nerve and cause a radiculopathy. If the annular fissure or annular tear is significant enough, disc material can herniate to irritate or compress transversing nerves or spinal cord. In either case, when the transversing nerve is irritated, it can cause radicular symptoms including pain, paresthesia, and/or weakness depending on the extent of nerve irritation or compromise.
An annular fissure can be concentric, transverse, or radial in orientation and may involve some or all layers. On MRI T2 sequence, the annular fissure is hyper intense (bright) compared to the rest of the annulus fibrosus (which is normally hypointense or dark) due to the relative increase in water content at the fissure compared to the normal annulus fibrosus.
If there is herniation of intravertebral disc material, there must be incompetence of the annulus fibrosus, and thus, an annular fissure or annular tear must be present even if not specifically visualized on the imaging. Thus, an annular fissure or annular tear can be implicated any time intravertebral disc herniation is identified.
If a patient is unable to have an MRI, a CT myelogram may show nerve root or cord compression from a disc protrusion. The CT scan can not identify the edema of an annulus fibrosus tear or fissure and thus, it is less sensitive than MRI.
An annular fissure or tear can be either symptomatic or asymptomatic. Symptomatic annular fissures can occur with or without intravertebral disc protrusion or herniation. Each entity is discussed separately below.
Asymptomatic Annular Tear
If the annular tear or fissure is identified incidentally, most commonly on MRI imaging, then no treatment is warranted. Such annular fissures may resolve spontaneously over time and are frequently due to the stresses applied to the spine. It is posited that some asymptomatic annular tears may become symptomatic with time, but there is currently no definitive evidence that treatment of asymptomatic annular tears provides any benefit or prevents any future issues.
Symptomatic Annular Tear without Disc Protrusion or Herniation
An annular fissure or tear can be symptomatic without disc protrusion or herniation. It is suspected that local inflammatory reactions from the annulus fibrosus tear or fissure lead to irritation of adjacent nerve fibers or transversing nerve roots. The mainstay of treatment for such situations is non-steroidal anti-inflammatory medications as well as low-impact physical therapy. The non-steroidal anti-inflammatory medications may help decrease the inflammatory reaction at the annular fissure which decreases stimulation or irritation of adjacent nerve fibers or transversing nerve roots. The low-impact physical therapy may help strength core muscles to mitigate the forces which may have originally led to the annular fissure or tear. Some have suggested local transforaminal steroid injections may alleviate the symptoms more quickly.
Some have argued that long-standing annular fissures or tears may lead to granulation tissue formation at the site of the annulus fibrosus tear or fissure. This local granulation tissue can either irritate or compress the transversing nerve root and lead to a radicular pattern of symptoms. The first-line treatment for such situations is non-steroidal anti-inflammatory medications and low impact physical therapy as discussed above with or without transforaminal steroid injection. In longer-standing cases, or instances with weakness or progression some suggest decompression of the nerve with a foraminotomy may prevent further deterioration and improve the symptoms. Some have suggested resecting the granulation tissue itself.
Symptomatic Annular Tear with Disc Protrusion or Herniation
If there is disc protrusion or herniation, it is usually the protruding or herniated disc material itself which causes the clinical symptoms. In such cases, the patient is treated for the disc protrusion or herniation and not the annular fissure or tear. Treatment options for disc protrusion or herniation including conservative measures of nonsteroidal anti-inflammatory medications, physical therapy, and local injections. If symptoms fail to improve, symptoms progress, or the patient develops weakness surgical treatment options should be considered including laminotomy, laminectomy, foraminotomy, discectomy, fusion, or some combination thereof. If a discectomy is performed there has been no convincing evidence that closure of the annular fissure, tear, or annulotomy significantly affects the long-term outcome for the patient.