- Small dimple in dorsal midline: Dermal sinus tracts occur in the lumbosacral midline above the intergluteal cleft and are commonly associated with other cutaneous as well as intradural pathologies (2, 9). When the skin orifice is very small, it may be missed on examination. In such cases, the use of magnification may be warranted. Often, a white creamy skin discharge is noted.
- Associated cutaneous signatures: Cutaneous stigmata that are associated with dermal sinus tracts include abnormal pigmentation, hemangioma, hypertrichosis, subcutaneous lipoma, and the exceedingly rare caudal appendage.
Infection can occur anywhere along the dermal sinus tract, from skin to spinal cord, as well as in extraspinal locations such as the mediastinum (10, 19).
- Local cutaneous infection: Erythema, swelling, and purulent drainage from spinal dermal sinus tracts may be present due to local or deep infections.
- Meningitis: Patients with meningitis, especially when it is recurrent or caused by unusual organisms, should be evaluated for midline cranial or spinal dermal sinus tracts (10). Meningitis was a common presentation in the past, but increased alertness of primary care physicians and the wide availability of precise neuroimaging modalities has made early diagnosis possible (1, 2, 16,17).
- Abscess: Abscesses can be extradural, subdural, and intramedullary, sometimes in association with an infected dermoid tumor (6, 20).
Complication of chemical or infective meningitis: Hydrocephalus has been reported with dermal sinus tracts, likely as a complication of meningitis and leptomeningeal inflammation. A chemical meningitis or ventriculitis from spillage of a dermoid tumor may result in hydrocephalus (13, 16).
- Frequent urological dysfunction: Urological problems as a result of a tethered cord syndrome or a postinfectious complication are not uncommon in patients with dermal sinus tracts, with up to 72% suffering from abnormal urodynamic findings (16). Radiological evaluation is less sensitive in confirming urological system abnormalities and has shown vesicoureteral reflux in only 24% of patients.
Differentiation from sacrococcygeal dimple
Differentiating dermal sinus tracts from the more common sacrococcygeal pits or dimples is important.
- Dimples in gluteal fold and pilonidal cysts: Sacrococcygeal dimples are simple blind sinuses without accompanying cutaneous abnormalities. They are located in the intergluteal cleft a few millimeters rostral to the tip of the coccyx. They have either a caudally or horizontally oriented course. They often contain hair and skin debris. The pilonidal cyst can be associated with obesity, hirsutism, trauma, irritation, poor hygiene, hyperhidrosis, and/or a family history.
- Not associated with intradural pathology: As they are not associated with intradural pathologies, these lesions do not require further neurosurgical investigation.
- Laboratory tests for inflammation: Inflammatory markers including ESR , CRP, and blood or urine culture can be helpful in identifying or confirming infections, as well as following the progress of treatment.
- Ultrasound can be useful up to age 6 months: Ultrasound is a well-known screening modality for spinal dysraphism in infants. The sinus tract, conus location, and associated pathology often can be defined with ultrasound. However, ultrasound is less reliable in patients older than 4–6 months with ossified posterior elements (8, 21). When a high-risk cutaneous anomaly is noted on examination, such as a lumbar dermal sinus tract opening, an MRI scan is essential.
Unless significant spinal bony anomalies are present, a spinal CT scan is not needed during evaluation of spinal dermal sinus tract.
MRI is the gold standard in determining the spinal level of the conus medullaris as well as the existence of associated anomalies including inclusion tumors or other tethering lesions (9, 16).
- MRI may miss the full extent of the tract: If dermal sinus tracts are complicated by infection in the intradural space, the anatomy will be disturbed, and MRI may be unable to define the level of the conus or related problems. A more complex signal heterogeneity pattern may occur when an inclusion tumor and an infection coexist (23).
- DWI scan for dermoid/epidermoid cysts: Inclusion tumors have variable signaling on T1- and T2-weighted images, and they usually restrict on diffusion weighted-imaging (DWI). Hyperintensity in the cord may indicate edema, abscess, or a pre-syrinx state. Contrast enhancement can help to identify infections.
T2-weighted sagittal MRI of lumbosacral spine: Shown is an intradural dermoid tumor tethering the spinal cord. The caudal tip of the conus is at the L3 level
Gadolinium-enhanced, T1-weighted sagittal MRI of the lumbosacral spine: This image is from a patient with sepsis and paraplegia. Note the extensive intradural abscess extending from the low thoracic region to S1
Nuclear Medicine Tests
- Not indicated
- Not indicated for routine cases
- Not indicated
Correlation of Tests
- Imaging: The presence of a dermal sinus tract on MRI (with and without gadolinium contrast) confirms the diagnosis. The MRI is inspected for the presence of inclusion cysts or abscesses.
- Clinical examination: Systemic, neurological, and urological evaluations determine the timing and type of surgery. Surgery is planned electively. However, the presence of a skin opening gives a sense of urgency to the surgery, as an infection is to be avoided. An infected tract should be treated with antibiotics prior to surgery.
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