Posterior Mediastinal Mass

Eric J. Crotty, MD

DIFFERENTIAL DIAGNOSIS

Common

Neural Crest Tumors
Lymphoma

Less Common

Nerve Sheath Tumors
Foregut Duplication Cyst

Rare but Important

Neurenteric Cyst
Meningocele
Paraspinal Abscess
Tumor
Esophageal Varices
Extramedullary Hematopoiesis

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Posterior mediastinal mass in young children should be considered neuroblastoma until proven otherwise

Helpful Clues for Common Diagnoses

Neural Crest Tumors
- Includes neuroblastoma, ganglioneuroma, and ganglioneuroblastoma, which demonstrate spectrum of cellular maturity and malignancy
  - Most neuroblastoma are immature, undifferentiated, and aggressive; occurs in younger population (median age < 2 years)
  - Ganglioneuroma most mature and least aggressive; occurs in older population (median age ˜ 7 years)
  - Ganglioneuroblastoma intermediate between neuroblastoma and ganglioneuroma
- Radiograph: Demonstrates elongated oval appearance with tapered borders in paraspinal location
- Homogeneously solid or may contain foci of calcification, which may be fine or chunky in appearance
- Separation or erosion of ribs and enlargement of neural foramina may be present
- CT better demonstrates calcification (40%)
- MR better demonstrates intraspinal extension
- Nuclear medicine imaging with methyl-iodobenzylguanidine (MIBG) labeled with I-131 or I-123 and bone scintigraphy is mainstay of diagnosis and for monitoring response to therapy
- PET/CT use is evolving and promising
Lymphoma
- Mediastinum is least common site of lymphoma
- Nearly always associated with sites in other mediastinal compartments

Helpful Clues for Less Common Diagnoses

Nerve Sheath Tumors
- Includes neurilemoma (schwannoma), neurofibroma (plexiform and nonplexiform types), and malignant schwannoma
- Sharply defined round, smooth, or lobulated paraspinal masses
- Homogeneous or heterogeneous attenuation on CT with mild heterogeneous enhancement
- Low to intermediate signal intensity on T1 with bright signal on T2 and mild enhancement following contrast administration
- Neurofibromata may have “target” appearance on T2 and inversion recovery sequences
  - Higher signal peripherally and intermediate signal centrally
- Neurofibromata are most commonly seen in neurofibromatosis type 1, where they are most commonly multiple
  - May be visible along intercostal nerves and in skin and subcutaneous tissues
  - Can distort ribs giving them ribbon-like appearance
- Plexiform neurofibromas are more infiltrative and may extend into middle mediastinum
Foregut Duplication Cyst
- Rounded fluid-filled mass with thin wall associated with esophagus
- Low attenuation on CT
  - No enhancement following contrast administration
- In general, ↓ signal on T1 and ↑ signal on T2
  - May have higher signal on T1 due to high protein content of fluid
- In correct position, indistinguishable from bronchogenic cyst by imaging

Helpful Clues for Rare Diagnoses

Neurenteric Cyst
- Contains both neural and gastrointestinal elements
- Associated with vertebral anomalies
Meningocele
- Herniation of leptomeninges through intervertebral foramen
- May be anterior or lateral in addition to (more common) dorsal
- Majority associated with neurofibromatosis, vertebral and rib anomalies
- Associated with spinal anomalies; may lead to kyphosis or scoliosis
- Fluid attenuation on CT
- Low signal on T1 with high signal on T2 and no enhancement with contrast
Paraspinal Abscess
- Discitis more common in preschool children and vertebral osteomyelitis in older children
- Staphylococcus aureus most common pyogenic organism; tuberculosis most common worldwide
- Discitis and osteomyelitis
  - Disc space narrowing with indistinct end plates
  - Paravertebral soft tissue mass
- Tuberculosis
  - Disc space narrowing often later than in pyogenic osteomyelitis
  - Gibbus deformity
Tumor
- Uncommon, except for lymphoma and neural tumors
- Primary (e.g., rhabdomyosarcoma) and secondary tumors (e.g., malignant melanoma) that can occur at nearly any site in body should be considered
Esophageal Varices
- Most commonly secondary to portal hypertension
- Paraspinal lobulated soft tissue mass
- Flow voids on MR with enhancement on MRA
Extramedullary Hematopoiesis
- 1 or more lobulated soft tissue masses in lower thoracic paraspinal region
- Homogeneous soft tissue attenuation on CT
- Homogeneous signal on MR with mild to moderate enhancement
- May have expanded ribs and vertebral bodies

Image Gallery

Anteroposterior radiograph shows a smoothly marginated oblong mass

in the left paraspinal location. There is no rib destruction or expansion. Calcifications are not identified.

Axial CECT shows a well-circumscribed soft tissue mass

in the posterior mediastinum. There are fine calcifications

within the mass, consistent with a neuroblastoma.

(Left) Axial T1WI C+ MR shows the mass

crossing midline and elevating the aorta

and invading 1 of the neural foramina

on the left. There is also evidence of invasion of the posterior thoracic wall on the left

. (Right) Coronal T2WI FSE MR in the same child shows a large mass

, predominantly within the posterior mediastinum, deviating the aorta to the right. Cystic areas of degeneration

are seen in this ganglioneuroblastoma.

(Left) Anteroposterior radiograph shows a smoothly marginated mass

in the superior left hemithorax. (Right) Coronal T1WI C+ FS MR shows an enhancing posterior mediastinal mass

. Note the neural foramina

with compression on the thecal sac

. MR is helpful in depicting neural foramina extension. Ganglioneuromas are benign tumors that may represent the end process of maturation of malignant neuroblastomas.

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