Misleading Rare Case of Idiopathic Hypertrophic Pachymeningitis

Idiopathic hypertrophic pachymeningitis (IHP) is a rare disease with diffuse thickening of the dura mater that has no specific clinical symptoms and manifestations and it causes neurosurgeons to misdiagnose. A 4-year-old girl presented at the emergency room of our hospital with speech difficulty and severe headache. Head computed tomography scans (CT scan) on admission revealed a large fluid collection over the right temporoparietal region with mass effect, and the neurosurgeon drained it with the initial diagnosis of subdural hematoma. However, the postoperative CT scan demonstrated the failure of surgical drainage; therefore, magnetic resonance imaging (MRI) was requested for the patient. MRI identified diffuse nodular dural thickening with internal septations and different internal hemorrhagic stages on the right side with no evidence of brain parenchymal involvement and according to the serology and autoimmune screening tests, and IHP was diagnosed for the patient. The patient underwent craniotomy. There was an immediate improvement of neurologic symptoms. The patient had good clinical and radiologic outcome at 3 -months follow-up. IHP should be part of the differential diagnosis of some cases of noncommunicating hydrocephalus; however, the rarity of the disease and the absence of specific clinical symptoms make the diagnosis difficult.


Introduction
Hypertrophic pachymeningitis (HP) is a neurological disease characterized by focal or difuse thickening of the dura mater, with or without infammation.Primary or idiopathic hypertrophic pachymeningitis (IHP) does not have an identifable cause.Secondary HP may follow a known cause such as trauma, infection (neurosyphilis, tuberculosis, fungal infections, syphilis, and Lyme's disease), tumors (dural carcinomatosis, meningiomaen plaque, and lymphoma), autoimmune diseases (Sjogren's and IgG4-related diseases and collagen vascular disorders), and miscellaneous disorders such as sarcoidosis, mucopolysaccharidosis, intracranial hypotension syndrome, and intrathecal drug administration [1,2].
IHP is an extremely rare disorder with nonspecifc clinical symptoms and manifestations, making diagnosis difcult [3].Herein, we present a case of IHP in a 4-year-old girl which caused the initially misdiagnosed as subdural hematoma.

Case Presentation
Our case report describes a 4-year-old girl who presented at the emergency room of Be'sat Hospital with left-side hemiplegia and seizure.Te patient had a history of hydrocephalus at birth and had a shunt implanted.Te patient was conscious during the physical examination.Vital signs included a body temperature of 37 °C, a heart rate of 112 beats per minute, a respiratory rate of 18 beats per minute, and a blood pressure of 110/70 mmHg.
She had a full neurological examination, which reveals aphasia and facial and left upper limb paresthesia.Her systemic examination was normal and in particular, there was no evidence of lymphadenopathy, organomegaly, or cutaneous features of connective tissue disease.Lumbar puncture showed increased intracranial pressure.
A head computed tomography scan (CT scan) was quickly requested for the patient, in which a large fuid collection over the right temporoparietal region with mass efect was observed, and the neurosurgeon drained it with the initial diagnosis of subdural hematoma (Figure 1(a)).However, the postoperative CT scan demonstrated the failure of surgical drainage due to the presence of a dural layer in the deep portion of the collection (Figure 1  2 Case Reports in Medicine Due to noncommunicating hydrocephalus, the patient was taken back to the operating room and underwent craniotomy surgery.A dural biopsy through a craniectomy was performed, which confrmed the diagnosis of IHP.Te patient experienced prompt clinical and neurologic improvement with the resolution of the preoperative symptoms related to increased intracranial pressure.Te patient was discharged home on 60 mg of prednisolone orally daily. She was reviewed in the outpatient clinic a month after discharge and was doing well.Her headaches and paresthesia had resolved completely.At 3 months from symptom presentation, while on a slow steroid taper (10 mg daily, 6 months weaning protocol), repeat imaging continues to demonstrate no active dural disease.

Discussion
IHP is an extremely rare disorder that predominantly afects male patients and is characterized by infammatory fbrosis and localized or difuse dura mater thickening without underlying disease [4,5].In patients with IHP, headache, nausea, and vomiting are the most common symptoms.Headache is mainly due to infammation of the dura mater but can also be due to raised intracranial pressure.Visual loss (due to optic neuropathy subsequent optic atrophy and the third, fourth, and sixth cranial nerves involvement), seizures, encephalopathy, and hemiparesis are other symptoms reported in IHP patients [6].
IHP mimicked other common neurologic conditions such as prolactinoma with recurrent vision loss, neurosarcoidosis, atypical lymphoplasmacytic-rich meningioma, lymphoplasmacytic-rich meningioma, subdural hematoma, and subacute subtentorial hematoma [5].IHP misdiagnosed as subdural hematoma is not uncommon; however, IHP presenting as subdural hematoma is unusual [7].In our case, the initial CT scan showed features of a subdural hematoma, leading the surgeon to make a misdiagnosis.
Te defnitive diagnosis is based on MRI or brain biopsy of the thickened dura mater.Biopsy reveals interstitial fbrosis and infammatory cell infltration.Enhanced MRI is the most valuable test in the diagnosis of IHP.When the dura is not obviously thick, IHP may not be diagnosed on a CT scan and/or MRI without contrast [8].Te lesions appeared hypointense or isointense on T1-weighted sequences, hypointense on T2-weighted sequences, hypointense on FLAIR sequences, and hypointense on DWI [9].
Postcontrast enhancement is usually seen.Enhanced MRI can be used to evaluate the efect of therapy [10].
Although no specifc protocol has been proposed for the treatment of IHP so far, however, by reviewing the available literature, two conservative treatment lines have been defned based on the disease mechanism, symptoms, and patient conditions.Te frst line of treatment includes the administration of steroids, prednisolone, with an initial dose of 42.7 mg/day and a maintenance dose of 12.4 mg/day for long-term treatment.In cases resistance to steroids or recurrence when steroids are tapered, an immunosuppressant, such as cyclophosphamide or methotrexate, is a second choice to treat steroid-refractory IHP [5].However, sometimes, conservative treatment is not efective enough to prevent severe complications in life-threatening conditions, such as noncommunicating hydrocephalus, prompt surgical intervention may be necessary.In our case, subtotal resection surgery was performed and then treatment with prednisolone was administered after pathologic diagnosis [11].
So far, including our case, this is the third reported case of IHP with hydrocephalus (Table 1) [12,13]. 2 cases were children and one case was an adult.In the reported cases, headache is the most common symptom of this disease.In the patient reported by Aburahma et al. [12], unlike our patient, the patient was treated with conservative treatment and without craniectomy.Also, our patient had good clinical and radiologic outcome at the 3 -months follow-up.

Conclusion
IHP should be a part of the diferential diagnosis of some cases of noncommunicating hydrocephalus; however, the rarity of the disease and the absence of specifc clinical symptoms make the diagnosis difcult.

Figure 1 :
Figure 1: Nonenhanced axial CT scan demonstrates large right temporoparietal fuid collection (a).Nonenhanced axial postop CT scan demonstrates failure of surgical drainage due to the presence of dural layer in deep portion of the collection (b).Follow-up nonenhanced axial CT scan showed interval hemorrhage (blue arrow) in the collection (c).

Figure 2 :
Figure 2: Sagittal T2W (a) and coronal T2W images demonstrated right pariental complex fuid collection with internal septation (blue arrow) and diferent internal hemorrhagic stages and mass efect (b).Axial FLAIR image demonstrated that collection over right temporoparietal extraaxial collection with mass efect has focal internal layering (c).Contrast-enhanced T1W image showed difuse nodular dural thickening and dural enhancement (orange arrow) (d).

Table 1 :
Summary of case reports on noncommunicating hydrocephalus with IHP.