Sacrococcygeal teratoma

Sacro-coccygeal teratoma (SCT) refers to a teratoma arising in the sacro-coccygeal region. The coccyx is almost always involved ⁶.

Demographics and clinical presentation

It is the commonest congenital tumour in the fetus ¹¹ and neonate ³. The incidence is estimated at ~1:35000-40000. There is recognised female predilection with a  M:F ratio of 1:4. Sacrococcygeal region is the commonest location for non CNS teratomas.

Pathology

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 2^nd to 3^rd weeks of gestation. There are most often mixed solid/cystic, although purely cystic types can occur in ~15% of cases.

The tumour is composed of the all three germ cells (i.e. ectoderm, mesoderm and endoderm)

Genetics

• most cases tend to be sporadic ¹²

Associations

• myelomeningocoele
• vertebral anomalies

Markers

Can have elevated levels of:

• alpha feto protein (AFP)
• beta HCG

Classification

A pathology-based classification is as:

• benign (mature): much more common, comprising ≈60-70%
• malignant (immature)

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 intra-pelvic pre-sacral extension
• type III: extra-fetal with abdomino-pelvic extension
• type IV: tumour developing completely in the fetal pelvis

Radiographic features

Plain film

• may show a large mass projecting from the lower pelvic region or within the abdominopelvic cavity
• may show calcification

CT

Not part of routine investigation. Identifies bone, fat and cystic components. Calcification may again be seen.

Ultrasound

Mature types tend to be more cystic which show as anechoic components. Solid types (which are much rarer) often show an echogenic mass within the pelvis.

The correlation between sonographic appearances and malignant components are thought to be poor ⁷.

Colour Doppler interrogation in some tumours may show marked hypervascularity with arterio-venous (AV) shunting.

MRI

Superior to ultrasound especially in assessment of the following areas ²:

• colonic displacement
• ureteric dilatation
• associated hip dislocation
• intraspinal extension
• vaginal dilatation
• 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 artifact because of calcifications
• T1 C+ (Gd): enhancing solid components

Complications

• high output cardiac failure from AV shunting: which in turn can cause hydrops fetalis
• ureteric obstruction
• gastro-intestinal tract obstruction
• compression of underlying nerves: giving urinary/faecal incontinence
• anaemia
• dystocia
• tumour rupture

Treatment and prognosis

An SCT can be benign or malignant depending on whether mature or immature. The majority however tend to be benign (~80% ¹¹). Those presenting in older infants tend to have a higher malignant potential which those presenting in utero have poor prognosis due to complications. Malignant change may be also commoner in males. Treatment is with surgical excision inclusive of coccygectomy with additional chemotherapy for malignant tumours ⁵.

Differential diagnosis

General considerations include:

• sacral chordoma
• terminal myelocystocoele: for cystic types on ultrasound ⁹
• sacral meningocoele

For type IV lesions also consider:

• low lying neuroblastoma
• low lying rhabdomyosarcoma
• small round blue cell tumour in sacral region
• enteric (tail gut) cyst: for a purely cystic SCT