Sacrococcygeal teratoma

Sacrococcygeal teratoma (SCT) refers to a teratoma arising in the sacrococcygeal region. The coccyx is almost always involved ⁶.

Epidemiology

It is the commonest congenital tumour in 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. The sacrococcygeal region is the commonest location for non-CNS teratomas.

Clinical presentation

Presentation varies depending on if a tumour has an intrapelvic location or has an extra-fetal extension (see further classification below). Intrapelvic tumours can manifest after birth with genitourinary and gastrointestinal symptoms given the compression of those structures. 

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. They are most often mixed solid/cystic, although purely cystic types can occur in ~15% of cases.

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

Genetics

• most cases tend to be sporadic ¹²

Associations

• myelomeningocele
• vertebral anomalies

Markers

Can have elevated levels of:

• alpha-fetoprotein (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 PediatricPaediatric 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: tumour developing entirely in the fetal pelvis

Radiographic features

Plain radiograph

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

CT

Not part of a 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 arteriovenous (AV) shunting.

MRI

Superior to ultrasound especially in the 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 artefact because of calcifications
• T1 C+ (Gd): enhancing solid components

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 a 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.

Complications

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

Differential diagnosis

General imaging differential considerations include:

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

For type IV lesions also consider:

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