====== 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.

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

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

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

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

===== Histopathology =====
  * **Microscopic Features**:
    - Spindle-shaped cells arranged in a "patternless" pattern.
    - Alternating hypocellular and hypercellular areas.
    - Thick collagen fibers.
    - High vascularity in hemangiopericytoma-like areas.

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

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

===== Molecular Testing =====
  * **NAB2-STAT6 Gene Fusion**:
    - A hallmark genetic alteration in SFTs.
    - 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.

===== Differential Diagnosis =====
  * SFTs may be confused with other tumors due to overlapping features.
  * Key differentials include:
    - **Meningiomas**: EMA-positive, CD34-negative.
    - **Schwannomas**: S100-positive, STAT6-negative.
    - **Neurofibromas**: S100-positive with different histological patterns.
    - **Sarcomas**: Higher grade, lack STAT6 staining.

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

===== Summary =====
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.



==== Imaging ====
  * **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.

==== Histopathology ====
  * 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).