2026 年 13 巻 p. 275-279
Detailed evaluation of language function is important in the management of dominant temporal lobe lesions. Although spoken language is routinely evaluated in patients, disturbances in written language may remain undetected without detailed assessment. The Japanese writing system, consisting of logographic Kanji and phonographic Kana, provides a unique framework for identifying selective impairments of the ventral language stream. We report a 51-year-old right-handed Japanese male who presented with selective agraphia for Kanji following a left posterior temporal subcortical hemorrhage. Upon admission, spontaneous speech was fluent, and auditory comprehension was preserved, with no clinically apparent aphasia. However, comprehensive neuropsychological assessment revealed a profound impairment in Kanji writing. Although standard language scores improved significantly by the chronic phase (Day 87), qualitative assessment revealed persistent deficits in Kanji retrieval, characterized by frequent non-responses and morphologically related errors. Conversely, Kana writing and reading abilities were largely preserved. This case demonstrates that selective impairment of written language (pure agraphia for Kanji) may occur in association with posterior temporal lesions, despite preserved spoken language. Unlike typical cortical lesions that destroy the orthographic representation itself, we propose that this specific subcortical hemorrhage caused a transient disconnection within the ventral language stream, selectively disrupting the semantic access pathway to Kanji. From a functional and clinical perspective, systematic evaluation of writing function is essential for neurosurgeons and clinicians to prevent overlooked disabilities.
Accurate assessment of language function is a central concern in the management of lesions involving the dominant temporal lobe. In routine clinical practice, language function is often judged primarily on the basis of spoken language, including fluency, comprehension, and repetition. Although this approach is sufficient for detecting overt aphasia, it may fail to identify selective disturbances of higher language functions.
Japanese written language consists of two distinct systems: Kanji, which are logographic characters closely linked to semantic processing, and Kana, which are phonographic symbols dependent on phonological processing.1) This linguistic characteristic allows precise functional localization of writing-related networks in focal brain lesions. Neuropsychological dissociations between Kanji and Kana writing suggest partially distinct neural substrates within the dominant temporal lobe.1) Lesions involving the posterior temporal region have been associated with selective impairment of Kanji writing, sometimes in the absence of clinically apparent aphasia.2-5) However, cases presenting with a purely subcortical etiology are rare, and the exact subcortical network mechanisms remain under debate. In this report, we describe a case of selective agraphia for Kanji associated with a left posterior temporal subcortical hemorrhage. We highlight the novelty of this case by discussing the pathomechanism, not merely as a cortical dysfunction, but as a subcortical network disconnection syndrome.
A 51-year-old right-handed Japanese male (occupation: food manufacturing manager) presented to our institution on Day 0 (day of onset). He had a past medical history of paroxysmal atrial fibrillation (status post-catheter ablation), hypertension, and sleep apnea syndrome. On the day of onset, while working at his office, he suddenly noticed difficulty in understanding documents and an inability to write Kanji, despite being able to read Kana. He also reported an occipital headache.
Neurological examinationOn admission, the patient was alert (Glasgow Coma Scale 15), with an elevated blood pressure (200/120 mmHg). Neurological examination revealed no motor weakness, sensory disturbance, or cranial nerve deficits. Spontaneous speech was fluent without dysarthria. Auditory comprehension was well preserved. The patient could read and write his own name in Kanji but was unable to write other Kanji characters, specifically noting an inability to write his wife's first name. Kana reading and writing were preserved.
Imaging findingsInitial computed tomography (CT) and magnetic resonance imaging performed on Day 0 revealed a subcortical hemorrhage (approximately 3 cm in diameter) in the left posterior temporal lobe, extending to the parietal region (Figure 1A-C). Three-dimensional CT angiography showed no evidence of vascular malformations or underlying tumors. The hemorrhage was attributed to hypertension.
Non-contrast head computed tomography (CT) scans.
(A-C) Images obtained on admission. (A) Axial, (B) sagittal, and (C) coronal views reveal a spontaneous intracerebral hemorrhage in the left temporal lobe, measuring 2.7 × 3.5 × 2.4 cm.
(D) Axial CT image obtained at discharge showing the absorption of the hematoma.
The patient was treated conservatively with strict blood pressure control, and was transferred to a rehabilitation facility on Day 27. Axial CT image obtained at discharge showed absorption of the hematoma (Figure 1D). Detailed neuropsychological assessments were conducted in close collaboration with a speech-language pathologist.
Initial assessment (Day 17)The Standard Language Test of Aphasia (SLTA) revealed that auditory comprehension (30/30) and repetition (13/15) were largely intact. However, naming was slightly impaired (18/20), and writing scores were reduced (10/16). Crucially, a detailed analysis of the writing subtests revealed a profound dissociation between Kanji and Kana (Figure 2). The patient achieved highly preserved correct response rates in Kana word tasks (80% [4/5] in writing and 100% [5/5] in dictation). In stark contrast, his performance in Kanji word tasks was selectively and severely impaired, with a correct response rate of only 20% (1/5) in both writing and dictation. Though the patient initially presented with alexia with agraphia, the reading impairment improved rapidly.
Comparison of writing performance between Kanji and Kana across Standard Language Test of Aphasia (SLTA) subtests.
The bar chart illustrates the correct response rates (%) for specific writing subtests (word writing and dictation) of the SLTA. On Day 17, a stark dissociation is evident, with Kanji performance severely impaired (20% in both writing and dictation) while Kana performance is highly preserved (80% and 100% in writing and dictation, respectively). By Day 87, Kanji scores demonstrated marked recovery, reaching the ceiling effect (100%) and matching the Kana scores across all domains.
General intelligence: The Wechsler Intelligence Scale-Third Edition showed a Full Scale intelligence quotient (IQ) of 91 (verbal IQ: 86 and performance IQ: 98), indicating no generalized intellectual decline. Visuospatial function: Rey Complex Figure Test score was 36/36, and Visual Perception Test for Agnosia was normal, ruling out apraxia or visuospatial agnosia. Dissociation of writing: A profound dissociation was observed. Kana writing was preserved with only minor speed reduction. In contrast, Kanji writing was severely impaired. In a task of writing 46 elementary-level Kanji, he scored 27/46 on Day 32. Qualitative analysis: The predominant error type in Kanji writing was non-response (inability to recall the character). Interestingly, the patient could successfully construct Kanji characters when provided with "radical" cards (e.g., combining semantic and phonetic components), indicating preserved morphological knowledge despite impaired spontaneous retrieval.
Follow-up and outcomeRe-evaluation with the SLTA on Day 87 demonstrated significant recovery in standard scores (Figure 3): naming improved to 20/20, repetition to 15/15, and reading comprehension to 40/40. To quantitatively assess the dissociation between Kanji and Kana writing, we analyzed the correct response rates for specific writing subtests of the SLTA (Figure 2). On Day 17, Kanji performance was severely impaired, with a correct response rate of 20% in both word writing and dictation. In stark contrast, Kana performance was highly preserved, scoring 80% in word writing and 100% in dictation. By Day 87, Kanji scores demonstrated marked recovery, reaching 100% in both subtests, thereby completely matching the Kana scores. However, qualitative clinical assessment revealed that difficulty with Kanji retrieval persisted in spontaneous writing tasks. The patient continued to exhibit morphological errors (e.g., substituting visually similar characters) and relied on digital tools.
Radar chart of the Standard Language Test of Aphasia (SLTA) profile. The solid line represents the profile on Day 17 (initial assessment), and the dashed line represents the profile on Day 87 (chronic phase). The chart illustrates a comprehensive recovery across most language domains, approaching the maximum scores (ceiling effect) in the chronic phase, although qualitative impairments in Kanji writing persisted.
The patient was discharged on Day 64, and returned to work on Day 110. Due to persistent difficulty with spontaneous Kanji retrieval, he utilized digital tools (smartphone dictionaries) to compensate for the writing deficit, and his vocational role was modified to field supervision.
This case demonstrates selective impairment of Kanji writing associated with a left posterior temporal lesion, despite preserved spoken language. This dissociation cannot be explained by a generalized language deficit, visuospatial dysfunction (as evidenced by the Rey Complex Figure Test), or motor impairment. Instead, it reflects disruption of the ventral language pathway within the dual-stream model of language processing.6) Although the hemorrhage was subcortical, it likely disrupted the cortico-subcortical connections of the posterior temporal language network.
This region, often referred to as the basal temporal language area, overlapping functionally with the visual word form area, acts as an interface between semantic memory and orthographic representations.7) Kanji writing relies heavily on access to lexical-semantic representations (ventral stream), whereas Kana writing utilizes dorsal phonological pathways.1,8) To clarify the pathomechanism, it is essential to distinguish between cortical epicenters and subcortical networks. Cortically, along with previous lesion studies by Sakurai et al.,4) direct electrical stimulation and functional mapping have confirmed that the posterior-inferior temporal cortex is a critical epicenter for processing Japanese Kanji.9,10) Subcortically, Duffau et al.11) highlighted the dynamic dual-stream model, wherein the ventral semantic stream is mediated by the inferior occipito-frontal fasciculus (IFOF) and the inferior longitudinal fasciculus (ILF). Enatsu et al.12) further demonstrated that the basal temporal language areas are functionally connected to frontal regions via these specific white matter pathways. Because Kanji writing strongly depends on semantic access, it strictly requires the integrity of these ventral white matter tracts to retrieve correct visual object forms. Several features of the patient's performance clarify the functional role of the posterior temporal cortex. Reading ability and Kana writing were largely preserved, and copying of Kanji characters was relatively better than spontaneous writing. These findings indicate intact visual analysis of character forms within the cortex and preserved motor execution. The primary deficit appears to lie at the interface between semantic representations and orthographic output.13,14) This suggests that the posterior temporal region serves as a convergence zone, linking meaning to written output rather than as a simple storage site for orthographic representations. Given the subcortical nature of the lesion, the hemorrhage likely disconnected the semantic system from the orthographic output lexicon by disrupting the aforementioned ventral white matter tracts (e.g., IFOF or ILF) rather than destroying the cortical epicenters, resulting in a clinical picture consistent with pure agraphia for Kanji in the chronic phase.
Diagnostic challenges and lessons for neurosurgeryFor neurosurgeons, this case underscores the limitations of relying solely on spoken language, or even on standard aphasia batteries, to evaluate language function.15) As seen in the Day 87 assessment, the patient achieved near-perfect scores on the SLTA due to the ceiling effect, yet significant vocational disability persisted due to Kanji agraphia, particularly in spontaneous writing tasks required in his managerial work. Preserved conversational speech may mask selective deficits in written language that are only revealed through qualitative and specific neuropsychological assessment.
ConclusionsSelective agraphia for Kanji may occur in association with left posterior temporal lesions, despite preserved spoken language. This case highlights the importance of detailed assessment of written language for accurate functional localization. Neurosurgeons must be aware that "fluent speech" does not equate to "intact language," and failure to assess the dissociation between logographic (Kanji) and phonographic (Kana) scripts may lead to the overlooking of significant vocational disabilities.
All authors have no conflict of interest.
Written informed consent was obtained from the patient for publication of this case report and any accompanying images.
