History :
A 54 y/o gentalman found to have a mass on the right buttock for 7 months. It was painful and may radiate to right thigh and lower leg.

Image finding :
MRI revealed a obulated mass arising from the sacrum coccyx junction. Pelvic CT with contrast enhancement shows : A large lobulated mass lesion located at the presacral space and extending to surrounding coccyx with destruction of the sacral bone. Calcified matrix is identified within this lesion.

Diagnosis :
Chordoma, Sacrococcyx

Discussion :
Sacrococcygeal Chordoma (50-70% of all chordoma)
40% of all sacral tumors
Peak age: 40-60 years; M:F = 2:1
*low back pain (70%)
*constipation / fecal incontinence
*rectal bleeding (42%) sciatica
*frequency, urgency, straining on micturition
*sacral mass (17%)

Location:esp. in 4th + 5th sacral segment
-presacral mass with average size of 10 cm extending superiorly + inferiorly; rarely posterior location
-displacement of rectum + bladder
-solid tumor with cystic areas (in 50%)
-osteolytic midline mass in sacrum + coccyx
-amorphous peripheral calcifications (15-89%)
-secondary bone sclerosis in tumor periphery (50%)
-honeycomb pattern with trabeculations (10-15%)
-may cross sacroiliac joint

Prognosis:
8-10 years average survival; 66% 5-year survival rate (adulthood)

DDx:
Giant cell tumor, plasmacytoma, lymphoma, metastatic adenocarcinoma, aneurysmal bone cyst, atypical hemangioma, chondrosarcoma, osteomyelitis, ependymoma

CT:
-low-attenuation within soft-tissue mass (due to myxoid-type tissue) -higher attenuation fibrous pseudocapsule

MR (modality of choice):
-heterogeneous low to intermediate intensity on T1WI, occasionally hyperintense (due to high protein content)
-very high signal intensity on T2WI (similar to nucleus pulposus with high water content)

NUC:
-cold lesion on bone scan
-no uptake on gallium scan
Prognosis:
almost 100% recurrence rate despite radical surgery