Prevalence: 1÷40,000 live births

• Most common presacral germ cell tumor in children!
• Most common congenital solid tumor in newborn!

Pathogenesis:

1. growth of residual primitive pluripotential cells derived from the primitive streak + knot (Hensen node) of very early embryonic development
2. attempt at twinning
   • increased prevalence of twins in family

Histo:

1. Mature teratoma (55–75%) with elements from glia, bowel, pancreas, bronchial mucosa, skin appendages, striated + smooth muscle, bowel loops, bone components (metacarpal bones + digits), well-formed teeth, choroid plexus structures (→ production of CSF)
   • MATURE TERATOMA = benign tumor composed of tissues foreign to anatomic site in which they arise, usually contains tissue from at least 2 germ cell layers
2. Immature teratoma (11–28%): admixed with primitive neuroepithelial / renal tissue
   • IMMATURE TERATOMA = benign teratoma with embryonic elements
3. Malignant germ cell tumor
   1. mixed malignant teratoma (7–17%): elements of endodermal sinus tumor (= yolk sac tumor) + either form of teratoma
   2. pure endodermal sinus tumor (rare)
   3. seminoma (dysgerminoma), embryonal carcinoma, choriocarcinoma (extremely rare)

Metastases to: lung, bone, lymph nodes (inguinal, retroperitoneal), liver, brain

Age: 50–70% during first few days of life; 80% by 6 months of age; <10% >2 years of age; rare in adulthood (only 100 cases reported); M÷F = 1÷4

• Older age means increased prevalence of malignancy (in 50–90% >2–4 months of age)!

Classification (Altman):

• Type I predominantly external lesion covered by skin with only minimal presacral component (47%)
• Type II predominantly external tumor with significant presacral component (35%)
• Type III predominantly sacral / abdominal component + external extension (8%)
• Type IV presacral tumor with no external component (10%)

• Internal component suggests malignant transformation!

Associated with: other congenital anomalies (in 18%):

1. Musculoskeletal (5–16%): spinal dysraphism, sacral agenesis, hip dislocation, clubbed feet
2. Renal anomalies: hydronephrosis, renal cystic dysplasia, Potter syndrome, urethral atresia, urinary ascites
3. GI tract: imperforate anus, rectal atresia / stenosis, gastroschisis
4. Hydrocolpos, undescended testes
5. Fetal hydrops ← high-output cardiac failure
6. Placentomegaly ← fetal hydrops
7. Curvilinear sacrococcygeal defect (rare autosomal dominant inheritance with equal sex incidence, low malignant potential, absence of calcifications) + anorectal stenosis / atresia, vesicoureteral reflux

• ↑AFP elevated with mixed malignant teratoma + endodermal sinus tumor (CAVE: fetal + newborn serum contains AFP, which does not reach adult levels until about 8 months of age)
• premature labor ← polyhydramnios + large mass
• uterus large for dates
• radicular pain, constipation, urinary frequency / incontinence
• asymptomatic / mass + pressure symptoms like constipation
• recurrent pilonidal infections

Average size: 8 (range, 1–30) cm in diameter

Plain film:

• amorphous, punctate, spiculated calcifications, possibly resembling bone (36–50%); suggestive of benign tumor
• soft-tissue mass in pelvis protruding anteriorly + inferiorly

BE:

• anterosuperior displacement of rectum
• luminal constriction

IVP:

• displacement of bladder anterosuperiorly
• development of bladder neck obstruction

Myelography:

• intraspinal component may be present

Angio:

• neovascularity (arterial supply by middle + lateral sacral + gluteal branches of internal iliac artery, branches of profunda femoris artery)
• enlargement of feeding vessels
• arterial encasement
• arteriovenous shunting
• early venous filling with serpiginous dilated tumor veins

US / CT:

• solid (25%) / mixed (60%) / cystic (15%) sacral mass
• polyhydramnios (⅔)
• poor prognostic factors : oligohydramnios, fetal hydrops with ascites, fetal hydronephrosis, pleural effusions, skin edema, placentomegaly

OB-US:

Age: as early as 14 weeks GA

• increased size of uterus ← mass / polyhydramnios
• rapid growth reaching enormous volumes:
  • assessment of tumor volume, amniotic fluid index, placental thickness, diameter of IVC, cardiothoracic ratio, pulmonary hypoplasia
• oligohydramnios ← obstruction of urinary tract
• arteriovenous shunting (Doppler US)

Cx (in 18%): preterm labor, preeclampsia, HELLP syndrome, premature delivery, dystocia, intratumoral hemorrhage, tumor avulsion → fetal exsanguination

Rx: US-guided drainage of cystic component, fetal surgery + Cesarean section for solid tumor

MR (preferred modality for initial Dx + surveillance):

• lobulated + sharply demarcated tumor extremely heterogeneous on T1WI ← high signal from fat, intermediate signal from soft tissue, signal void from Ca²⁺
• best modality to detect spinal canal invasion

Prognosis: likely benign: predominantly fatty / cystic tumor

likely malignant: hemorrhagic / necrotic tumor, sacral destruction, patient >2 months of age

Mortality: 5% for infant; 50% for fetus (worse <30 weeks GA)

Cx:

1. Dystocia in 6–13%
2. Massive intratumoral hemorrhage
3. Fetal death in utero / stillbirth

Rx:

1. Complete tumor resection + coccygectomy + reconstruction of pelvic floor: up to 37% recurrence rate, esp. without coccygectomy
2. Multiagent chemotherapy (in malignancy) with long-term survival rate of 50%

DDx:

1. Myelomeningocele (superior to sacrococcygeal region, not septated, axial bone changes)
2. Rectal duplication, anterior meningocele (purely cystic)
3. Hemangioma, lymphangioma, lipomeningocele, lipoma, epidermal cyst, chordoma, sarcoma, ependymoma, neuroblastoma