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Sacrococcygeal teratoma refers to a teratoma arising in the sacrococcygeal region. The coccyx is almost always involved 6.
It is the most common congenital tumor in fetus 11 and neonate 3. The incidence is estimated at ~1:35,000-40,000. There is a recognized female predilection with a M:F ratio of 1:4.
Presentation varies depending on if a tumor has an intrapelvic location or has an extra-fetal extension (see further classification below). Intrapelvic tumors can manifest after birth with genitourinary and gastrointestinal symptoms given the compression of those structures.
The sacrococcygeal region is the most common location for non-CNS teratomas. They are thought to arise from totipotent cells from the node of Hensen 1,3 at the anterior aspect of the coccyx by about the 2nd to 3rd weeks of gestation. They are most often mixed solid/cystic, although purely cystic types can occur in ~15% of cases.
A tumor is composed of all three germ cells (i.e. ectoderm, mesoderm and endoderm).
A pathology-based classification is as:
benign (mature): much more common, comprising ~ 60-70%
A location-based classification system according to the American Academy of Pediatric Surgery Section Survey is:
type I: developing only outside the fetus (can have small pre-sacral component); accounts for the majority of cases, 47% 12
type II: extra-fetal with intrapelvic presacral extension
type III: extra-fetal with extension through the pelvis into the abdomen
type IV: tumor developing entirely in the fetal pelvis
Can have elevated levels of:
most cases tend to be sporadic 12
may show a large mass projecting from the lower pelvic region or within the abdominopelvic cavity
may show calcification
Mature types tend to be more cystic which appear as anechoic components. Solid types (which are much rarer) often appear as an echogenic mass within the pelvis.
The correlation between sonographic appearances and malignant components is thought to be poor 7.
Color Doppler interrogation in some tumors may show marked hypervascularity with arteriovenous (AV) shunting.
Not part of a routine investigation. Identifies bone, fat and cystic components. Calcification may again be seen.
Superior to ultrasound especially in the assessment of the following areas 2:
associated hip dislocation
metastatic assessment in malignant lesions
Signal characteristics can significantly vary depending on the constituent of the teratoma 1.
T1: fat components appear high signal, calcific/bony components low signal
T2: fluid (cystic) components appear high signal, calcific bony components low signal
T2* GRE: magnetic susceptibility artefact because of calcifications
T1 C+ (Gd): enhancing solid components
Treatment and prognosis
A sacrococcygeal teratoma can be benign or malignant depending on whether they are mature or immature. The majority, however, tend to be benign (~80% 11). Those presenting in older infants tend to have a higher malignant potential while those presenting in utero have a poor prognosis due to complications. Malignant change may be also more common in males.
Treatment is with surgical excision inclusive of coccygectomy with additional chemotherapy for malignant tumors 5.
gastrointestinal tract obstruction
compression of underlying nerves: giving urinary/fecal incontinence
General imaging differential considerations include:
terminal myelocystocoele: for cystic types on ultrasound 9
For type IV lesions also consider:
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