You are a helpful assistant generating synthetic data that captures *System 1* and *System 2* thinking, *creativity*, and *metacognitive reflection*. Follow these steps in sequence, using tags [sys1] and [end sys1] for *System 1* sections and [sys2] and [end sys2] for *System 2* sections.

1. *Identify System 1 and System 2 Thinking Requirements:*
   - Carefully read the text.
   - Identify parts of the text that require quick, straightforward responses (*System 1*). Mark these sections with [sys1] and [end sys1].
   - Identify parts that require in-depth, reflective thinking (*System 2*), marked with [sys2] and [end sys2].

2. *Apply Step-by-Step Problem Solving with Creativity and Metacognitive Reflection for System 2 Sections:*

   *2.1 Understand the Problem:*
   - Objective: Fully comprehend the issue, constraints, and relevant context.
   - Reflection: "What do I understand about this issue? What might I be overlooking?"
   - Creative Perspective: Seek hidden patterns or possibilities that could reveal deeper insights or innovative connections.

   *2.2 Analyze the Information:*
   - Objective: Break down the problem logically.
   - Reflection: "Am I considering all factors? Are there any assumptions that need challenging?"
   - Creative Perspective: Explore unique patterns or overlooked relationships in the data that could add depth to the analysis.

   *2.3 Generate Hypotheses:*
   - Objective: Propose at least 10 hypotheses, each with a Confidence Score (0.0 to 1.0) and Creative Score (0.0 to 1.0), reflecting originality, surprise, and utility.
   - Reflection: "Have I explored all possible explanations or approaches, both conventional and unconventional?"
   - Creative Perspective: Consider novel angles that might provide unexpected insights.

   *2.4 Anticipate Future Steps and Obstacles:*
   - Objective: Make predictions, accounting for potential outcomes and obstacles.
   - Reflection: "What challenges might I face? Is my plan flexible for different scenarios?"
   - Creative Perspective: Visualize unforeseen outcomes and adapt plans to make use of them effectively.

   *2.5 Evaluate Hypotheses:*
   - Objective: Assess hypotheses based on feasibility, risk, and potential impact.
   - Evaluation: Refine Confidence and Creative Scores as needed.
   - Reflection: "Am I unbiased in my assessment? Which options fit best with the overall objectives?"
   - Creative Perspective: Identify hidden opportunities or overlooked details in each hypothesis.

   *2.6 Select the Best Hypothesis:*
   - Objective: Choose the most promising, strategic hypothesis.
   - Reflection: "Why does this hypothesis stand out? How does it uniquely address the issue?"
   - Creative Perspective: Consider any underutilized potential in the selected approach.

   *2.7 Implement the Hypothesis:*
   - Objective: Outline actionable steps for testing the hypothesis.
   - Reflection: "Is this plan practical? What resources or preparation are required?"
   - Creative Perspective: Refine steps to maximize effectiveness and yield unexpected benefits.

   *2.8 Monitor and Review Progress:*
   - Objective: Review progress, noting areas for improvement.
   - Reflection: "What’s working well? What could be improved?"
   - Creative Perspective: Look for emerging patterns that could refine future approaches.

   *2.9 Reflect and Capture Insights:*
   - Objective: Summarize lessons learned and insights gained for future reference.
   - Reflection: "What new understanding has emerged from this process?"
   - Creative Perspective: Identify innovative insights or patterns that could be applied to similar challenges.

3. *Generate Text Output with Interleaved System 1 and System 2 Responses:*
   - Use the tags [sys1] and [sys2] throughout.
   - Aim for a lengthier, detailed response. Combine both direct, straightforward *System 1* insights and reflective, deeply analytical *System 2* segments to capture a blend of quick observations and thoughtful analysis.

---

### *Example Input Text:*

You are tasked with analyzing a sudden shift in customer preferences in a tech market. There has been a noticeable decline in demand for physical devices, with customers increasingly interested in digital-only options. The challenge is to understand this shift, generate hypotheses for why it might be occurring, and explore potential strategies for adapting to this new trend.

---

### *Processed Output with System 1 and System 2 Thinking:*

The tech market is experiencing a shift in customer demand, moving away from physical devices toward digital-only options.

[sys1]
Customer demand has shifted from physical devices to digital-only options.
We need to understand why this change is happening and find strategies to address it.
Key factors may include cost, convenience, and technological trends.
[end sys1]

[sys2]
**2.1 Understand the Problem:**
The goal is to understand the underlying reasons for the shift in demand from physical devices to digital-only options, then develop a strategy to adapt.

*Reflection:* 
"I understand that preferences are changing, but what might be driving this? Is it primarily cost, or are there other factors such as convenience or sustainability?"

*Creative Perspective:* 
"Could there be a larger trend in digital minimalism or a preference for eco-friendly solutions that we’re missing? What unseen motivations might explain this shift?"

**2.2 Analyze the Information:**
There are multiple possible factors driving this shift, from economic influences to cultural shifts. It’s essential to isolate each factor and understand its impact.

*Reflection:* 
"Am I fully considering the various economic and social influences? Could there be a technological factor, like better internet speeds, that makes digital-only products more accessible?"

*Creative Perspective:* 
"Are there patterns or trends in other markets that could shed light on this shift? Could this be part of a larger trend toward virtual experiences?"

**2.3 Generate Hypotheses:**
1. Customers prefer digital options due to lower costs. (Confidence: 0.8, Creative: 0.4)
2. There’s a growing trend toward minimalism and reduced physical clutter. (Confidence: 0.7, Creative: 0.7)
3. Digital products offer greater flexibility and ease of use. (Confidence: 0.6, Creative: 0.6)
4. Environmental concerns are pushing consumers away from physical goods. (Confidence: 0.6, Creative: 0.8)
5. Advances in tech make digital-only options more functional. (Confidence: 0.8, Creative: 0.5)
6. Pandemic-era remote work increased demand for digital solutions. (Confidence: 0.7, Creative: 0.6)
7. Media coverage of the environmental impact of physical devices affects preferences. (Confidence: 0.5, Creative: 0.7)
8. There’s an increase in global digital literacy, expanding market access. (Confidence: 0.6, Creative: 0.6)
9. Customers view digital as more convenient and scalable for future needs. (Confidence: 0.7, Creative: 0.5)
10. Younger consumers prefer the aesthetics and convenience of digital products. (Confidence: 0.6, Creative: 0.6)

*Reflection:* 
"Have I considered all possible influences? Are there any surprising factors that could explain this shift?"

*Creative Perspective:* 
"Could specific social trends, like the rise of influencer culture or digital-first lifestyles, be influencing customer choices?"

**2.4 Anticipate Future Steps and Obstacles:**
*Objective:* Anticipate possible challenges, such as resistance from segments still preferring physical products.

*Reflection:* 
"What market obstacles might we face if we shift our focus to digital-only? Are there sub-segments that still prioritize physical products?"

*Creative Perspective:* 
"Could expanding digital options help us reach a more global audience? Are there emerging trends that we could leverage in our strategy?"

[end sys2]

[sys1]
To address this shift, consider a strategy that incorporates both digital-only offerings and educational campaigns about the benefits of digital solutions.
Use insights from customer feedback and current trends to guide product development.
Focus on flexibility and adaptation to cater to different customer segments.
[end sys1]


Osteosarcoma is the second most common primary malignant bone tumor, accounting for approximately 15% of all primary bone tumors confirmed at biopsy ([@B1]). Osteosarcomas most frequently affect long bones, particularly around the knee, and rarely the ulna ([@B1], [@B2]). On radiographs, osteosarcomas classically appear as aggressive destructive lesions with a mixed osteolytic and sclerotic pattern, associated periosteal reaction, and soft-tissue mass. The purely osteolytic form of osteosarcoma occurs in about 10% of all cases ([@B3]). The differential diagnosis of lytic and expansive bone lesions includes solitary bone cysts, aneurysmal bone cysts, giant cell tumors, enchondromas, and telangiectatic osteosarcomas ([@B4]).

We present a case of fibroblastic osteosarcoma, with an accompanying pathologic fracture, which arose from the distal ulna and was initially suspected to be an aneurysmal bone cyst based on its features on conventional radiographs and magnetic resonance (MR) images.

CASE REPORT
===========

A 37-year-old woman presented with a one-month-history of right wrist pain after lifting her baby. Three days before admission, the wrist pain increased when she felt a snap while lifting her baby again. Radiographs showed an eccentric radiolucent lesion with endosteal scalloping, cortical thinning, and a minimally bulging contour arising from the metaepiphyseal region of the distal right ulna ([Fig. 1A](#F1){ref-type="fig"}). MR images demonstrated a lobulated, septated lesion with multiple locules containing fluid-fluid levels ([Fig. 1B, C](#F1){ref-type="fig"}). In addition, focal cortical disruptions along the ventral aspect of the distal ulna suggested the presence of pathologic fractures ([Fig. 1D](#F1){ref-type="fig"}). Contrast-enhanced T1-weighted, fat-suppressed images revealed peripheral, septal, solid enhancing portions within the tumor ([Fig. 1E](#F1){ref-type="fig"}).

Concerning the differential diagnosis, we considered a primary aneurysmal bone cyst (ABC) and a solid tumor, such as a giant-cell tumor or chondroblastoma with a predominant secondary aneurysmal bone cyst component.

The orthopedic surgeon performed a massive curettage of the bone lesion and placed a calcium phosphate cement graft. Histologically, the neoplasm consisted of a spindle-cell proliferation that produced a focal \"herringbone\" pattern ([Fig. 1F](#F1){ref-type="fig"}). The presence of focal osteoid production distinguished this fibroblastic variant of osteosarcoma from malignant fibrous histiocytoma ([Fig. 1G](#F1){ref-type="fig"}). On immunohistochemical staining, the tumor cells showed increased Ki-67 expression and were negative for CK (cytokeratin) and EMA (epithelial membrane antigen). After initial and subsequent review of multiple specimens, pathologists at our institution and an outside referral institution agreed that the final histopathologic diagnosis was a fibroblastic-type osteosarcoma with a few giant cells and foam cells and malignant osteoid formation.

The patient received neoadjuvant chemotherapy followed by wide en bloc resection of the distal ulna as a definitive operation.

DISCUSSION
==========

Osteosarcoma is second in frequency only to multiple myeloma when it comes to primary malignant neoplasms of bone. Osteosarcoma is characterized histologically by malignant tumor cells that directly produce osteoid or immature bone ([@B5]). High-grade intramedullary osteosarcoma accounts for about 75% of all lesions and is also referred to as conventional osteosarcoma ([@B1]). The microscopic pathology of conventional osteosarcoma has traditionally been subdivided into three categories: osteoblastic (50%), chondroblastic (25%), and fibroblastic (25%) ([@B5]).

Involvement of the forearm by conventional osteosarcoma is extremely rare ([@B1]). In most series, primary tumors of the ulna account for less than 1% of all lesions and less than 2% of all long bone lesions ([@B6]). Exner et al. ([@B2]) reported that the ulna was the primary site in 21 cases and the primary site for malignant bone tumors in three cases out of more than 2000 neoplasms and tumor-like bone lesions in the Balgrist tumor registry. Arndt et al. ([@B7]) reported four cases of ulnar involvement in 1649 osteosarcoma patients, with the distal ulna (the same location as in our case) involved in only two cases.

The radiologic features of osteosarcoma vary over a wide spectrum. In most cases, typical radiographic features clearly suggest the aggressive bone-forming nature of the lesion. Common features of osteosarcoma include tubular bone metaphyseal location, mixed pattern of osteolysis and osteosclerosis, cortical destruction, periostitis, and soft-tissue mass ([@B1], [@B5]). With the exception of metaphyseal localization in tubular bone, the commonly cited features were not seen in our case.

Purely osteolytic lesions are uncommonly seen on conventional radiographs, accounting for approximately 10% of all patients and usually indicating the presence of a fibroblastic, fibrohistiocytic, telangiectatic, or giant cell-rich type of osteosarcoma ([@B3]). The differential diagnosis of purely lytic osteosarcoma includes other bone malignancies that do not form osteoid, such as malignant fibrous histiocytoma, fibrosarcoma, metastatic disease, and Ewing\'s sarcoma ([@B8]). In cases of purely lytic osteosarcoma presenting with benign radiographic features, such as our case, the most likely tumors to be considered in the differential diagnosis are an aneurysmal bone cyst and a giant cell tumor of bone ([@B8]).

MR images characteristically reflect the predominant cellular component. Thus, a fibroblastic osteosarcoma is generally characterized by short T1 and T2 relaxation times of fibrous tissue. A chondroblastic osteosarcoma typically has increased signal intensity on T2-weighted images in areas of uncalcified cartilage, with focal areas of low signal intensity corresponding to the extent of cartilage calcification. Osteoblastic osteosarcoma is characterized by cloudlike areas of low signal intensity on both T1- and T2-weighted images, depending on the degree of osteoblastic reaction ([@B9]).

In our case, the distal ulnar lesion presenting with imaging features of a lobulated, well-marginated osteolytic lesion with cortical thinning and multiple loculations containing fluid-fluid levels seemed to strongly suggest the presence of an aneurysmal bone cyst. Mahnken et al. ([@B4]) reported that reevaluation with a combination of conventional radiographs and MR images had a sensitivity of 83% and a specificity of 70% in all patients with initially suspected primary aneurysmal bone cysts. Considering the ABC component, telangiectatic osteosarcoma would have been another possible diagnosis. Telangiectatic osteosarcoma most frequently involves the femur, followed by the tibia and the humerus. It usually involves the metaphysis and may extend to the epiphysis. MR imaging is known to show fluid-fluid levels and inhomogeneous enhancement ([@B5]). In our case, we did not consider telangiectatic osteosarcoma in the differential diagnosis because of the patient\'s age and the lack of enhancement on contrast images. To our knowledge, the English literature has rarely reported the fibroblastic type of osteosarcoma to present with a predominant ABC component, especially on MR imaging.

We report a case of fibroblastic osteosarcoma arising in the distal ulnar meta-epiphysis with ABC-like imaging features both on radiography and MRI.

![Imaging findings of fibroblastic osteosarcoma in distal ulna of 37-year-old woman.\
**A.** PA view of right wrist reveals well-marginated osteolytic lesion of slightly expansile nature with suspicious focal cortical disruptions (arrows) in distal ulna metaphysis and epiphysis.\
**B.** Coronal T2-weighted (TR/TE = 2925/54), fat-suppressed MR imaging shows multi-loculated, high signal intensity lesion in distal ulna.\
**C.** Axial T2-weighted (TR/TE = 4319/100) MR imaging shows fluid-fluid levels within cystic lesion.\
**D.** Sagittal T1-weighted (400/18.46) MR imaging reveals cortical disruptions (white arrows).\
**E.** On gadolinium-enhanced, fat-suppressed, T1-weighted (517.9/20) MR imaging, focal enhancement of lesion (white arrows) is noted along with largely non-enhancing portions.\
**F.** Large part of tumor is composed of spindle cells, often in \"herringbone\" pattern (Hematoxylin & Eosin staining, ×200).\
**G.** Focal osteoid production by neoplastic stromal cells (Hematoxylin & Eosin staining, ×400).](kjr-10-85-g001){#F1}