Sacrococcygeal teratoma

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

Epidemiology

It is the most common congenital tumor in the fetus ¹¹ and neonate ³. The incidence is estimated at ~1:35,000-40,000. There is a recognized female predilection with a male-to-female ratio of 1:4.

Associations

• myelomeningocele

• vertebral anomalies

Clinical presentation

Presentation varies depending on whether a tumor has an intrapelvic location or 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. 

Pathology

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

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 intrapelvic presacral extension

• type III: extra-fetal with extension through the pelvis into the abdomen

• type IV: tumor developing entirely in the fetal pelvis

Markers

Can have elevated levels of:

• alpha-fetoprotein (AFP)

• beta HCG

Genetics

Most cases tend to be sporadic ¹².

Radiographic features

Plain radiograph

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

• may show calcification

Ultrasound

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.

CT

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

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/SWI: magnetic susceptibility artifact 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.

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/fecal incontinence

• anemia

• dystocia

• tumor rupture

Differential diagnosis

General imaging differential considerations include:

• sacral chordoma

• terminal myelocystocoele: for cystic types on ultrasound ⁹

• sacral meningocele

• sacral hemangioma

For type IV lesions also consider:

• low-lying neuroblastoma

• low-lying rhabdomyosarcoma

• small round blue cell tumor in the sacral region

• enteric (tailgut) cyst: for a purely cystic SCT