INTRODUCTION
Dermal sinus represents an abnormal communica- tion between dermis and intravertebral or intracra- nial structures. They are remnants of incomplete neural tube closure and are lined with epithelium.
Although dermal sinus can occur from the upper cervical region to the midsacrum, it is most com- monly found in the lumbar or lumbosacral area and may connect at any point with the central nervous system.
Some dermal sinuses end blindly within the soft tissues superficial to the underlying lamina; howev- er, most penetrate the vertebral canal and enter the dura immediately beneath, or to the cutaneous lesion. From this point the dermal sinuses extend cephalad to a variable degree, ending as high as the conus medullaris.
The tract leading to the vertebral column or skull may have a cystic termination (dermoid, epider- moid) or may be associated with spinal cord tether- ing. The cystic expansion may act as any other mass lesion and affect neurological function by local com- pression, or it may obstruct the normal circulation of cerebrospinal fluid. A small sinus ostium may be overlooked on physical examination, and frequently the diagnosis is not considered until a child has suf- fered unexplained or recurrent meningitis, rapid spi- nal cord compression, or evidence of a rapidly expanding intracranial mass. Therefore, the entire midline area of the skin from the skull to the sacro- coccygeal region should be examined carefully for evidence of a dermal sinus. Cutaneous anomalies are frequently present and include skin dimples, hairy patches and nevi skin tags, subcutaneous lipomas or haemangiomas. Bacterial infection can occur through the sinus because all midline skin pits above the intergluteal fold are assumed to communicate with the intrathecal sac.
Recommended investigations include convention- al X-ray films of the lumbosacral spine which may demonstrate spina bifida or dysraphic lesions, including vertebral anomalies or diastematomyelia.
The usefulness of plain radiographs may be limited because of immature calcification in children less than 18 months of age. Ultrasonography readily dem- onstrates the subcutaneous tract, intraspinal inclu- sion tumours, and diminished cord pulsations. The infection risk from probe insertion or injection of radiographic contrast agents into dermal sinuses is not justified and provides little diagnostic informa- tion. Invasive contrast studies have largely been replaced by magnetic resonance imaging (MRI), which visualizes in three dimensions the extra spinal tract path, inclusion tumours and other malforma- tions associated with spinal cord tethering, and pro- vides greater sensitivity than contrast-enhanced tomography (CT) and non-invasively confirms the diagnosis of dermal sinuses and associated malfor- mations. In patients with abnormal neurologic examination, bladder function is studied with renal/bladder ultrasound, urodynamic studies, and dynamic contrast voiding studies.
It is important to distinguish between the sacral dermal sinus and pilonidal sinus. Dimples below the top of the intergluteal crease are sacral pits. They end blindly and superficially and, regardless of their depth, never extend intraspinally; therefore, they require no investigation other than physical exam- ination. They are encountered in nearly 5% of new- borns and although they are present from birth, they rarely manifest themselves before adult life. In later years, these small pits or dimples may become pilo- nidal sinuses or abscesses.
Andrew B. Pinter 428
Figure 40.1
After induction of general anaesthesia and place- ment of a Foley catheter into the bladder, the patient is positioned prone with lateral padded rolls sup- porting the chest and abdomen. The arms of chil- dren less than 2 years of age are best supported alongside the trunk, whereas in older patients eleva- tion above the shoulder positions the surgeon closer to the patient. Betadine solution is used to prepare the skin from the intergluteal fold to many spinal lev-
Figure 40.2
The subcutaneous tissue is divided to expose the fas- cial defect, and the sinus stalk is circumferentially dissected. Cephalad to the stalk, the paraspinal mus- cles are elevated with electrocautery in a subperios-
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els above the sinus tract. Peri-operative administra- tion of intravenous antibiotics is strongly recom- mended.
An elliptical skin incision encircling the sinus opening, and any abnormal skin surrounding it, is made to excise fully the dermal sinus. Purulent mate- rial or drainage should be cultured in aerobic and anaerobic medium.
teal fashion from the first intact spinous process and lamina. Preparations must be made to continue bone removal across several laminae until the site of attachment to the dura is identified.
Figure 40.2
Andrew B. Pinter 430
Figure 40.3
If imaging studies indicate that the lesion penetrates deeper than the fascia or if this is observed intra- operatively, the dissection should proceed along the tract until its termination is reached.
The dura is opened with an elliptical incision encompassing the tract. Some sinus tracts abruptly end with dural attachment, which is readily apparent after dural opening. In these cases after confirming normal intradural anatomy, the dura is closed and the wound closed in layers. When the stalk continues
and intradural lesions such as a dermoid or epider- moid cyst, tethered spinal cord are present then the dissection must proceed into intradural space.
Further dissection is performed with loop or micro- scope magnification. Dissection of the stalk from this disordered glial mass may be accomplished using sharp microsurgical technique.
Intra-operative ultrasonography is useful for identifying syringomyelia or intramedullary der- moid at site of stalk attachment.
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Figure 40.4
Regardless of the attachment anatomy, a comprehen- sive inspection should be carried for arachnoid adhesions, dermoid tumours, and a thickened filum terminale. Dermoid inclusion tumours are frequent- ly multiple and can be solidly adherent to the filum and nerve roots within the cauda equina, especially when meningitis has occurred.
Intradural cysts are completely removed, without opening if this is possible and does not endanger ner- vous elements. Intraspinal and adherent intradural cysts are emptied of their contents and as much as possible removed. However, attempts to remove the hard fibrous capsule densely adherent to neural issue or capsule of infected intraspinal cysts are fruitless and may lead to additional and avoidable cord or root injury. Duraplasty performed if necessary and the muscles and skin are closely approximated without drainage. Drainage of an extradural abscess after operation may be necessary. Incompletely resected dermoid tumours may grow slowly over time, and the
density of post-operative adhesions and scar preclude total resection at re-operation.
Following complete tract and inclusions tumour resection, the subarachnoid space should be irrigat- ed with a saline solution. Dermoid and epidermoid debri are highly irritative to the spinal fluid, and this manoeuvre may diminish post-operative inflamma- tory meningitis. If an intramedullary mass has been resected the pia-arachnoid might be sutured and the tubular spinal cord reconstituted. To minimize post- operative spinal cord tethering, a dural patch graft is incorporated to ensure a wide contact of cerebrospi- nal fluid around the lower spinal cord and cauda equina. Fibrin glue may be employed if necessary.
The wound is closed in layers, and the paraspinal muscle fascia is reapproximated with running and interrupted sutures in a watertight manner. Skin clo- sure with vertical mattress sutures is preferred, espe- cially if there has been previous infection.
Dura Arachnoidea
Dermal sinus
Dermoid, epidermoid in the spinal cord (cauda equina)
Figure 40.4
Andrew B. Pinter 432
CONCLUSION
Conservative management of dermal sinuses is not justified, and these lesions should be electively resected at the time of diagnosis, because they may lead to progressive neurologic deterioration.
Dermal sinuses above the intergluteal crease should be surgically excised at the time of diagnosis in all patients prior to deficits to maintain neurolog- ic function, regardless of patient age. If the lesion is discovered during an episode of meningitis, lamino- plasty and intradural exploration should follow after infection has been controlled by antibiotics.
Emergency surgery is required in cases of rapid neu- rologic deterioration, recurrent infection during antibiotic therapy, or when infection cannot quickly be controlled.
The foundations of surgical repair are based on the embryology and anatomy of the malformations.
Surgical treatment consists of excision of the dimple and the tract from the skin surface to the deepest projection, as well as intradural connections or masses even when MRI reveals normal findings.
Chance of preserving the neurological function is high (95.4%).
Post-operative complications are limited follow- ing intradural exploration and complete resection of sinus tracts and cutaneous elements. Regardless of patient age, post-operative infection is the most common complication, and neurological deficits or cerebrospinal leaks can frequently occur after open- ing the dura. The prognosis in those patients who already have some neurological deterioration is fre- quently unfavourable, although some improvement may occur in the majority of the patients. Therefore, the surgery is done to prevent neurological deficit in those who do not have it. In patients with incomplete tumour resection, yearly follow-up MRI is recom- mended.
Optimum management of children requires close co-operation between pediatricians, pediatric sur- geons, neurosurgeons and multiple specialists involved with congenital defects and infectious dis- eases.
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SELECTED BIBLIOGRAPHY
Elton S, Oakes WJ (2001) Dermal sinus tracts of the spine.
Neurosurg Focus 10 : 1–4
Hattori H, Higuchi Y, Tashiro Y (1999) Dorsal dermal sinus and dermoid cysts in occult spinal dysraphism. J Pediatr 134 : 793
Kanev PM, Park TS (1995) Dermoids and sinus tracts of the spine. Neurosurg Clin North Am 6 : 359–366
Weprin BE, Oakes WJ (2000) Coccygeal pits. Pediatrics 105 : E69
