Diagnosis of Solitary Fibrous Tumors (SFTs)

The diagnosis of solitary fibrous tumors (SFTs) relies on a combination of clinical presentation, imaging studies, histopathology, and molecular analysis. Accurate diagnosis is critical due to their rarity and potential for variable behavior, ranging from benign to malignant.

• Symptoms:
  1. Dependent on tumor location.
  2. Spinal SFTs:
     1. Spinal pain (most common).
     2. Neurological symptoms such as radiculopathy, motor weakness, or sensory deficits due to spinal cord or nerve root compression.
     3. Urinary dysfunction in advanced cases.
• Onset:
  1. Slow and progressive in most cases, with occasional acute presentations (e.g., hemorrhage or rapid growth).

• Magnetic Resonance Imaging (MRI):
  1. Preferred modality for diagnosis and surgical planning.
  2. T1-weighted images: Iso- to hypointense compared to muscle.
  3. T2-weighted images: Iso- to hyperintense; may appear hypointense in highly fibrous tumors.
  4. Contrast enhancement: Homogeneous, intense enhancement after gadolinium administration.
  5. Additional Features:
     1. Displacement of adjacent structures (e.g., spinal cord compression).
     2. Dumbbell-shaped tumors in cases with foraminal extension.

• Computed Tomography (CT):
  1. Useful for evaluating bony involvement and calcifications.
  2. Often used in conjunction with MRI for preoperative assessment.

• Angiography:
  1. May be utilized to evaluate tumor vascularity, particularly for highly vascular lesions.

• Microscopic Features:
  1. Spindle-shaped cells arranged in a “patternless” pattern.
  2. Alternating hypocellular and hypercellular areas.
  3. Thick collagen fibers.
  4. High vascularity in hemangiopericytoma-like areas.

• Grading:
  1. Determined based on cellularity, mitotic activity, necrosis, and pleomorphism.
  2. Classified as Grade I (benign), Grade II (intermediate), or Grade III (malignant).

• STAT6 Nuclear Staining:
  1. Positive STAT6 staining is highly specific and diagnostic for SFTs.
• Additional Markers:
  1. Positive: CD34, Bcl-2, vimentin.
  2. Negative: S100 (to exclude schwannomas), EMA (to exclude meningiomas).

• NAB2-STAT6 Gene Fusion:
  1. A hallmark genetic alteration in SFTs.
  2. Confirmed using techniques such as next-generation sequencing (NGS) or fluorescence in situ hybridization (FISH).
• Molecular testing is especially useful in cases with atypical histology or immunohistochemical results.

• SFTs may be confused with other tumors due to overlapping features.
• Key differentials include:
  1. Meningiomas: EMA-positive, CD34-negative.
  2. Schwannomas: S100-positive, STAT6-negative.
  3. Neurofibromas: S100-positive with different histological patterns.
  4. Sarcomas: Higher grade, lack STAT6 staining.

• Preoperative diagnosis is difficult due to the nonspecific clinical and imaging features.
• Diagnosis often requires histological and molecular confirmation post-resection.

The diagnosis of solitary fibrous tumors involves:

• Imaging: MRI with gadolinium is the gold standard.
• Histopathology: Patternless architecture and spindle cells.
• Immunohistochemistry: Positive STAT6 nuclear staining.
• Molecular Testing: NAB2-STAT6 gene fusion for confirmation.

Accurate and early diagnosis enables appropriate treatment planning, including surgical resection and, if necessary, adjuvant therapies.

• MRI (Preferred modality):
  • Iso- to hypointense signal on T1-weighted images.
  • Variable signal on T2-weighted images (often hypointense due to fibrous content).
  • Strong, homogeneous enhancement with gadolinium.
  • May exhibit a “dural tail sign” similar to meningiomas.
• CT Scan:
  • Useful for detecting bone involvement or calcification.

• SFTs are composed of spindle cells arranged in a “patternless” pattern with alternating hypocellular and hypercellular areas.
• Immunohistochemical markers:
  • Positive: STAT6, CD34, Bcl-2, and vimentin.
  • Negative: S100 (helps differentiate from schwannomas or neurofibromas).