nasal dermal sinus is a very rare congenital anomaly that is frequently associated with inclusion cysts ( dermoid or epidermoid).1 
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 3 at the end of the second month of gestation , the nasal and frontal bones are separated by the fonticulus frontalis . in this period , the dura projects into the nasal area through the anterior skull base opening ( foramen cecum ) , and lies in contact with the skin at the tip of the nose . failure during ossification to obliterate this transcranial connection is the embryological pathway to nasal dermal sinus tract development.1 
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 4 in the present case , combined use of high resolution magnetic resonance imaging and computed tomography ( ct ) clearly demonstrated the detailed anatomical relationship of the dermal sinus associated with a dumbbell - shaped dermoid to the surrounding structures such as the fonticulus frontalis and foramen cecum.3 
 5 the patient was a boy aged 1  year and 4 months who had had a small pit at his nasion from birth and had developed swelling of the forehead . 1a ) . the sagittal view of a t2-weighted image demonstrated a dumbbell - shaped , mixed intense dermoid at the foramen cecum . the sinus tract was depicted as a strand of isointensity between the dermoid and the nasion . a subcutaneous abscess was noted adjacent to the dermoid , and the subcutaneous swelling of the forehead was demonstrated as hyperintensity ( fig . serial sagittal views of t1-weighted images ( t1wi ) revealed the capsule of the dermoid enhanced with contrast medium ( gadolinium - diethylenetriamine penta - acetic acid [ gd - dtpa ] ) , and that the subcutaneous abscess was in continuity with the dermoid cyst . on axial view of the gd - enhanced t1wi , the subcutaneous abscess was also noted adjacent to the dumbbell - shaped dermoid ( fig . serial sections of the sagittal and coronal ct scans clearly showed an enlarged fonticulus frontalis and foramen cecum remnant and dehiscence of the crista galli ( fig . 1f , g , h ) . three - dimensional ct imaging showed a bony defect at the midline of the junction of the frontal bone and the anterior fossa , with a bifid and bulging crista galli ( fig . ( a ) photograph showing the swelling of the forehead . the black arrow indicates a small pit on the nasion . inset is the magnified view of the pit , which seems to be closed and has no purulent discharge . there is a dumbbell - shaped mixed intense dermoid ( white arrow ) at the junction of the frontal bone and the anterior fossa ( at the foramen cecum ) , and a strand of isointensity ( nasal sinus tract ) between the tumor and the nasion . an abscess in the subcutaneous tissue of the forehead ( black asterisk ) is noted adjacent to the dermoid . the capsule of the dermoid is enhanced with contrast medium ( gd - dtpa ) . the dermoid is dumbbell - shaped ( white arrow indicates the neck of the dumbbell ) . both the dermoid ( white arrow ) and subcutaneous abscess ( black asterisk ) are demonstrated as a hyperintensity . ( f , g , h ) serial sections of the sagittal ( f , h ) and coronal ( g ) computed tomography scan . the enlarged fonticulus frontalis remnant ( white arrow ) , enlarged foramen cecum remnant ( white dotted line ) , and dehiscence of the crista galli ( white arrow heads ) are clearly visible . a bony defect is evident at the midline of the junction of the frontal bone and the anterior fossa with bifid crista galli ( white arrow heads ) . ( j ) schematic drawing demonstrating the anatomical relationship of the dermoid ( d ) , subcutaneous abscess ( a ) , and swelling ( s ) with surrounding structures . the subcutaneous abscess was evacuated through a coronal skin incision on the frontal region , and then the purulent dermoid cyst including the capsule was removed . the part of the dermoid capsule that was tightly adherent to the dura was carefully coagulated . ( a ) intraoperative photograph taken after removal of the dermoid through a coronal skin incision showing the bony defect ( white arrows ) . inset is a three - dimensional computed tomography image shown in the same orientation as ( a ) the white box indicates the extent of the operative field . ( b ) the sinus tract including the pit at the nasion was dissected with a tiny skin incision . the dermoid cyst wall is lined by a keratinizing squamous epithelium ( white asterisk ) . intraluminal keratin ( black asterisk ) and hair shafts ( black arrow ) are also demonstrated . the nasal sinus tract is a ductal structure ( black star ) lined by stratified squamous epithelium . the patient was a boy aged 1  year and 4 months who had had a small pit at his nasion from birth and had developed swelling of the forehead . 1a ) . the sagittal view of a t2-weighted image demonstrated a dumbbell - shaped , mixed intense dermoid at the foramen cecum . the sinus tract was depicted as a strand of isointensity between the dermoid and the nasion . a subcutaneous abscess was noted adjacent to the dermoid , and the subcutaneous swelling of the forehead was demonstrated as hyperintensity ( fig . serial sagittal views of t1-weighted images ( t1wi ) revealed the capsule of the dermoid enhanced with contrast medium ( gadolinium - diethylenetriamine penta - acetic acid [ gd - dtpa ] ) , and that the subcutaneous abscess was in continuity with the dermoid cyst . on axial view of the gd - enhanced t1wi , the subcutaneous abscess was also noted adjacent to the dumbbell - shaped dermoid ( fig . serial sections of the sagittal and coronal ct scans clearly showed an enlarged fonticulus frontalis and foramen cecum remnant and dehiscence of the crista galli ( fig . 1f , g , h ) . three - dimensional ct imaging showed a bony defect at the midline of the junction of the frontal bone and the anterior fossa , with a bifid and bulging crista galli ( fig . ( a ) photograph showing the swelling of the forehead . the black arrow indicates a small pit on the nasion . inset is the magnified view of the pit , which seems to be closed and has no purulent discharge . there is a dumbbell - shaped mixed intense dermoid ( white arrow ) at the junction of the frontal bone and the anterior fossa ( at the foramen cecum ) , and a strand of isointensity ( nasal sinus tract ) between the tumor and the nasion . an abscess in the subcutaneous tissue of the forehead ( black asterisk ) is noted adjacent to the dermoid . the capsule of the dermoid is enhanced with contrast medium ( gd - dtpa ) . the dermoid is dumbbell - shaped ( white arrow indicates the neck of the dumbbell ) . both the dermoid ( white arrow ) and subcutaneous abscess ( black asterisk ) are demonstrated as a hyperintensity . ( f , g , h ) serial sections of the sagittal ( f , h ) and coronal ( g ) computed tomography scan . the enlarged fonticulus frontalis remnant ( white arrow ) , enlarged foramen cecum remnant ( white dotted line ) , and dehiscence of the crista galli ( white arrow heads ) are clearly visible . a bony defect is evident at the midline of the junction of the frontal bone and the anterior fossa with bifid crista galli ( white arrow heads ) . ( j ) schematic drawing demonstrating the anatomical relationship of the dermoid ( d ) , subcutaneous abscess ( a ) , and swelling ( s ) with surrounding structures . the subcutaneous abscess was evacuated through a coronal skin incision on the frontal region , and then the purulent dermoid cyst including the capsule was removed . the part of the dermoid capsule that was tightly adherent to the dura was carefully coagulated . ( a ) intraoperative photograph taken after removal of the dermoid through a coronal skin incision showing the bony defect ( white arrows ) . inset is a three - dimensional computed tomography image shown in the same orientation as ( a ) the white box indicates the extent of the operative field . ( b ) the sinus tract including the pit at the nasion was dissected with a tiny skin incision . the dermoid cyst wall is lined by a keratinizing squamous epithelium ( white asterisk ) . intraluminal keratin ( black asterisk ) and hair shafts ( black arrow ) are also demonstrated . the nasal sinus tract is a ductal structure ( black star ) lined by stratified squamous epithelium . 1j demonstrates the detailed anatomical relationship between the sinus tract with dumbbell - shaped dermoid and the surrounding structures . the body of the dumbbell - shaped dermoid was located in the enlarged fonticulus frontalis and foramen cecum remnant ; the head of the dumbbell was the intracranial extension of the dermoid with bulging dura . a bifid and bulging crista galli was also attributed to the intracranial extension of the dermoid . although bacteriologic examination failed to reveal the causative agents , the microscopically opened sinus tract resulted in the formation of the subcutaneous abscess adjacent to the purulent dermoid .
nasal dermal sinus is a rare congenital anomaly . 
 we report a case of the dermal sinus associated with a dumbbell - shaped dermoid and demonstrate the detailed anatomy . 
 the patient was a boy aged 1  year and 4 months with a small pit at his nasion from birth and developed swelling of the forehead . 
 the sagittal view of a t2-weighted image demonstrated a dumbbell - shaped , mixed intense dermoid at the foramen cecum . the sinus tract was depicted as a strand of isointensity between the dermoid and the nasion . 
 serial sagittal views of t1-weighted images revealed the capsule of the dermoid enhanced with contrast medium , and that the subcutaneous abscess was in continuity with the dermoid . on diffusion - weighted imaging , 
 both the dermoid and subcutaneous abscess were demonstrated as a hyperintensity . 
 serial sections of the sagittal and coronal computed tomography scans clearly showed an enlarged fonticulus frontalis and foramen cecum remnant and dehiscence of the crista galli . the purulent dermoid cyst including the capsule and the dermal sinus tract were removed completely . 
 we describe our detailed anatomical relationship between the sinus tract with dumbbell - shaped dermoid and the surrounding structures , and emphasize the importance of these anatomy for operation .